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Shixue Dou (University of Wollongong) Xiaolin Wang (University of Wollongong) Hans-Ulrich Habermeier (Max Planck Institute for Solid State Research) Hiroaki Kumakura (National Institute of Materials Science) Robert Stamps (The University of Western Australia) Germanas Peleckis (University of Wollongong) |
Symposium Sponsors
ARNAM
University of Wollongong
Symposium Proceeding Details
1) The proceedings of the Symposium R will be published in International Journal of Modern Physics B (IJMPB).
2) Each participant willing to publish will be required to pay extra 50$ publication charge as this is not covered by registration fee.
3) The guidelines on the preparation of camera ready manuscripts can be found here: http://www.worldscinet.com/ijmpb/mkt/guidelines.shtml
4) The deadline for manuscript submission is September 30th, 2008.
5) A peer-review process will be organized for all manuscripts.
* Invited presentation
Chair: S.X. Dou
Monday, July 28, 2008
Level 2 - State Room, Hilton Sydney
11:00 AM *R1-S2.1 (invited)
Hybrid Material Hybrid Temperature Digital-RF Electronics Systems. (#1303) Oleg A Mukhanov,
HYPRES, Inc., Elmsford, New York, USA.
Digital-RF technology is a disruptive technological innovation capable of changing wireless communications, radar, and surveillance system architectures dramatically. Impressive results have been achieved in proving that superconductor Digital-RF technology can be practically applied to such systems altering the way these systems have been traditionally built. In these systems, fundamental advantages of superconductor materials translate into system benefits through enabling direct digital processing of wide band, high radio frequency (RF) signals and expanding digital domain throughout the entire system. In order to make superconductor electronics practical, we introduce the Hybrid Technology Hybrid Temperature (ht2) system integration concept that allows an effective combination of different technologies and materials co-located at different temperature stages of a 4 Kelvin cryocooler. Recently major breakthroughs have been achieved in the development, demonstration, and successful delivery of the cryocooled superconductor Digital-RF receivers directly digitizing signals in a broad range from kilohertz to gigaherts. The demonstrated cryocooled Digital-RF systems are the world's first and fastest directly digitizing receivers operating with live satellite signals in X-band and performing signal acquisition from HF to L-band with ~30 GHz clock frequencies.
11:15 AM *R1-S2.2 (invited)
Electrical Engineering Applications of HTSC-Fault Current Limiters and Magnetic Energy Storage. (#1276) Chris Cook,
The University of Wollongong, New South Wales, Australia.
This prsentation will review recent developments in electrical engineering applications of high temperature superconductors (HTSC). Some large contracts world wide have recently been written to provide fault current limiters (FCL) and superconducting magnetic energy storage devices (SMES) for electric untilities, and so HTSC applications are enjoying a resurgance. Australian Superconductors, which has recently become a part of a world wide company, Zenergy, is undertaking advanced research in both FCL and SMES, some of which is involving the University of Wollongong with support of grants from the Australian Research Committee. This has lead to refinements of HTSC coil designs, and also in the the controlling electronics, for FCL's and SMES. Work is also underway to gain a better understanding of how these devices will interact with the electricity grid. Some of the work on coil design is also being applied to HTSC coils to produce very large magnetic fields for Magnetic Resonant Instruments. Recent research and experimentation at Wollongong in all these areas will also be dicussed in this presentation.
11:30 AM *R1-S2.3 (invited)
Formation Mechanism of Semi-Crystalline Defect Traps in Self-Aligned Nanostructured MgB2. (#692) Sean Li,
The University of New South Wales, Sydney, Australia.
In this work, we report the formation mechanism of semi-crystalline defect wells in self-aligned nanostructured MgB2. It is demonstrated that these aperiodic regions trap numerous crystal defects migrating along nanodomain boundaries during self-alignment and act as intense vortex pinning centers that significantly enhance the high-field performance of MgB2. This suggests that the density of trapped defects in the wells is much greater than found in other vortex pinning sources.
11:45 AM *R1-S2.4 (invited)
Transmission Electron Microscopy Analysis of Nanostructured MgB2 Films Fabricated Using an Electron Beam Evaporation Technique. (#1245) Satoshi Hata1, Harini Sosiati1, Takeshi Yoshidome1, K Ikeda1, H Nakashima1, T Doi2, Y Tsukano2, H Yamashita2, Y Hidaka2, Y Hakuraku2, K Takahashi3, H Kitaguchi3;
1Kyushu University, Fukuoka, Japan
; 2Kagoshima University, Japan
; 3National Institute for Materials Science, Japan.
Nanostructures in MgB2 films are relatively controllable than those in other MgB2 materials such as tapes and wires. Therefore, MgB2 films can be candidates for fundamental research on the superconductivity as well as for practical applications. Kitaguchi and Doi et al. [1] fabricated as-grown MgB2 films with high critical current density Jc using an electron beam evaporation (EBE) technique. They introduced various kinds of nanostructures in the EBE MgB2 films to obtain better Jc properties under magnetic fields [2, 3]. In the present study, these nanostructured EBE MgB2 films have been investigated by transmission electron microscopy (TEM). Flux rates of Mg and B during the EBE process strongly influence nanostructure in the MgB2 film and its environmental stability. For example, MgB2 films fabricated under B-rich compositions than the MgB2 stoichiometry show columnar MgB2 crystals (10-50 nm in size) that are stable against exposure in the air. On the other hand, MgB2 films fabricated under off-stoichiometric Mg-rich compositions tend to show inhomogeneous microstructures, and deterioration of the MgB2 films occurs in the air. Such findings are valuable from the viewpoint of practical applications of the EBE MgB2 films. Doping with oxygen during the EBE process increases Jc under magnetic fields applied from arbitral directions. The MgB2 film fabricated under an optimum oxygen partial pressure (~1.3x10-5 Pa) shows columnar grains of MgB2, as observed in a non-doped film. Nanosized enrichment of oxygen was recognized at both inter- and intra-granular regions in the MgB2 film. An excess oxygen partial pressure degrades crystallinity of the columnar MgB2 and increases amounts of MgO and MgB4, resulting into decrease of Jc. Alternate deposition of MgB2 (15-50 nm) and Ni (~0.4 nm) or B (~5 nm) at a low temperature (~523 K) to form MgB2/X (X = Ni or B) multilayered nanostructure markedly increases Jc under magnetic fields applied parallel to the substrate surface. The matching field showing the maximal force of flux pinning can be controlled by changing the spacing between the X layers. It was also noted that the critical temperature monotonically decreases with reducing the spacing between the X layers. This work was supported in part by Research Promotion Bureau, Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan, under the contracts: No.19-174. TEM analysis was carried in ″Nanotechnology Support Project″ of the MEXT, Japan. [1] H. Kitaguchi et al.: Appl. Phys. Lett. 85 (2004) 2842. [2] T. Doi et al.: IEEE Trans. Appl. Supercond. 17 (2007) 2899. [3] T. Doi et al.: Supercond. Sci. Technol. 20 (2007) 1223.
12:00 PM *R1-S2.5 (invited)
Chemical Aspect of the Sodium Cobalt Oxyhydrate Superconductor. (#236) Eiji Takayama-Muromachi,
International Center for Materials Nanoarchitectonics, National Institute for Materials Science, Japan.
The sodium cobalt oxyhydrate NaxCoO2-yH2O has been studied intensively since the discovery of a superconducting transition below about 5 K. Superconductivity is induced in a CoO2 layer having a triangular lattice of Co and superconductivity is believed to be of an unconventional type. Not only physicists but chemists are interested in this superconductor because of its unique structure where water molecules are inserted between the Co planes making the system strongly two-dimensional and soft-chemical processes at room temperature which play an essential role in its synthesis. It has been discovered by NMR and NQR studies that a magnetically ordered phase is located just next to the superconducting phase implying that the superconductivity has a certain magnetic origin. In order to elucidate the rather complicated superconducting phase diagram of the system, detailed studies from the view point of chemistry is indispensable. The superconductor is synthesized by the soft chemical technique from the parent oxide of Na0.7CoO2. The soft chemical route includes two processes, the chemical oxidation using bromine (Br2) and hydration in water. It has been shown recently that the second process is not really a simple hydration. Actually, in the second process, a part of the sodium ions are exchanged by the oxonium (H3O+) ions and furthermore reduction the Co ions by water occurs forming additional H3O+ ions. Namely, two side reactions of ion exchange and reduction occur besides the intercalation of water molecules. Corresponding to this, the exact chemical formula of the superconducting phase is Nax(H3O)zCoO2-yH2O rather than NaxCoO2-yH2O which has been used widely. We succeeded to prepare samples with controlling x and z and draw superconducting phase diagrams of the system taking z/x as a parameter and keeping the Co valence constant. A phase diagram obtained showed that two superconducting phases of SC1 and SC2 exist sandwiching a magnetically ordered phase M supporting the results of NMR and NQR. The diagram also suggests strongly that magnetic correlation is the origin of superconductivity but superconductivity is suppressed in too strong correlation, and instead, magnetic order takes its place.
12:15 PM R1-S2.6
Latest Development on MgB2 Superconductors. (#1468) Shixue Dou,
University of Wollongong, Australia.
-
LUNCH 12:30 PM - 2:00 PM
Chair: C. Cai
Monday, July 28, 2008
Level 2 - State Room, Hilton Sydney
2:00 PM *R1-S3.1 (invited)
Improvement of Grain Connectivity and Critical Fields of MgB2 Superconductors by Co-Doping with CaB6 and Si. (#1122) Sonja Schlachter, Antje Frank, Alexandra Jung, Brigitte Runtsch, Heinrich Orschulko, Bernd Ringsdorf, Wilfried Goldacker;
Institut für Technische Physik, Forschungszentrum Karlsruhe GmbH, Eggenstein-Leopoldshafen, Germany.
One reason for the reduced Jc values of MgB2 PIT conductors compared to the values obtained in the best thin films is bad grain connectivity due to secondary phases and thick oxide layers at grain boundaries. Due to the high melting temperature of boron, the reaction of Mg and B is a liquid-solid or even a solid-solid reaction which often causes incomplete reaction of the precursor materials. Oxide layers, e.g. MgO or B2O3 which are often present on the grain surface of the precursor materials, can hinder the phase formation and act as barriers to transport currents. Recently, it could be shown that Jc can be strongly enhanced by CaB6 doping. It was speculated that CaB6 binds and removes oxides from the grain boundaries leading to an increase of the effective cross section. In contrast to SiC-doping the increase of Jc by CaB6-doping is nearly field-independent at 4.2 K. Co-doping with CaB6 and SiC was introduced as a promising way to 'clean' the material from oxide barriers with one component and to raise the upper critical field with the other addition. With this method not only the high-field Jc could be improved, but also the current carrying capability in low magnetic fields. We discuss the mechanisms leading to the enhancement of Jc and show how the Jc(B) dependence and the percolation degree can be tailored in a systematic way by co-doping with CaB6 and SiC.
2:15 PM *R1-S3.2 (invited)
Effective Chemical Approaches for Excellent Jc Characteristics of HTSC and MgB2. (#873) Jun-Ichi Shimoyama, Shigeru Horii, Hiraku Ogino, Kohji Kishio;
University of Tokyo, Bunkyo-ku, Japan.
In this paper, we show various effective methods to improve critical current properties of cuprates, such as RE123 and Bi-based compounds, and MgB2, developed through our recent studies. For cuprates, the stoichiometric cation composition giving the highest Tc should be achieved in the superconducting matrix somehow. This is a quite important factor for RE123 with light RE elements and Bi-based compounds, because these compounds usually have unintentional nonstoichiometry in cation compositions. In addition, it was confirmed that dilute impurity doping and/or low level cation-site exchange always effective for improving critical current properties particularly in high fields. The most effective combinations of dilute doping for improving intragrain Jc of RE123, Bi(Pb)2212 and Bi(Pb)2223 are Co or Ga to Cu in the CuO chain, RE with small ionic size for Ca and Nd or Pr for Sr, respectively. On the other hand, increases of grain boundary density and bulk density are effective for enhancement of Jc in low fields for polycrystalline MgB2. Suitable amount of carbon substitution for boron improves in-field Jc. By combining these facts, our dense MgB2 bulks synthesized by the premix PICT-diffusion method[1] exhibited record-high Jc at 20 K as for bulk MgB2. Furthermore, small amount of silver addition was found to dramatically decrease formation temperature of MgB2 without loosing high-Jc performance. Details of how we achieve high Jc characteristics for RE123 (single crystals, melt-solidified bulks and films), Bi(Pb)2212 single crystals and Bi(Pb)2223 sintered bulks including practical tapes will be shown based on our recent results. [1] I. Iwayama et al., Physica C 460-462 (2007) 581.
2:30 PM *R1-S3.3 (invited)
Guideline for the Fabrication and the Evaluation of the Grain Connectivity for Obtaining Ex Situ MgB2 Tapes with High Jc-B Performance. (#607) Takayuki Nakane, Hiroaki Kumakura;
National Institute for Materials Science, Japan.
For upgrade the Jc-B performance of ex situ MgB2 tape, there are a lot of issues. For the fabrication process, improving the quality of starting MgB2 powder is the important issue. However, clear guidelines have not yet been established for the powder preparation. Therefore, we investigated the relationship between the preparation condition of MgB2 powder and the Jc-B performance of ex situ tape fabricated from the prepared MgB2 powder. This study reveals the importance of the pelletizing pressure of precursor mixture before sintering process of MgB2 powder. The pelletizing pressure affects the growth of MgB2 grains, and the difference in the grain growth influences the grain connectivity core of end-product ex situ tape.
On the other hand, the core of ex situ tape is essentially a pressurized MgB2 powder without sintering process, therefore the grain connectivity of ex situ tape core is extremely poorer than that of the other formed samples such as the polycrystalline bulk, the in situ tape cores and the films. Therefore, the evaluation of the grain connectivity in MgB2 core is of increasing importance in this field. For discussing the grain connectivity of MgB2, some evaluation methods are proposed and utilized. However, the advantage and the disadvantage of these methods are not well discussed yet. Therefore, we evaluated the grain connectivity of prepared MgB2 samples (ex situ tape cores and pressurized pellets) with several methods, and the results were compared.
The grain connectivity of prepared samples were evaluated by using (a) the amplitude dependence of the superconducting transition curve for AC susceptibility, (b) current dependence of the superconducting transition curve for electrical resistivity and (c) the conductivities determined from the temperature dependence of the normal state electrical resistivity.
We found that (a) and (b) are convenient methods, even though they are useful only for qualitative discussion. However the experimental results under magnetic field are not reliable in case of (a). On the other hand, the comparisons by using absolute value are very meaningful, hence (c) are useful for quantitative discussion. However, difficulty (or failure) of the sample preparation sometimes made us hard for obtaining reliable and reasonable results. In addition, (c) using the resistivity data of non-superconducting state is strongly influenced by the conductivity of impurity phases.
These studies indicate the importance of parallel usage of some evaluation methods with taking account for their characteristics, appropriately. Moreover, all evaluation methods indicates that the grain connectivity of MgB2 pellets strongly depends on the pelletizing pressure. It means that we must check at first the change (or uniformity) in the core density of samples for the reasonable discussion or the grain connectivity of MgB2 core in ex situ MgB2 tape.
This work was supported by KAKENHI (No. 40354302: Grant-in-Aid for Young Scientists (B): the Ministry of Education, Culture, Sports, Science and Technology).
2:45 PM *R1-S3.4 (invited)
Self-Propagating High Temperature Synthesis (SHS) of Fine Boron Powders for Superconducting MgB2 Composite Wires. (#1040) Jaimoo Yoo1, Young-Kuk Kim1, Kookchae Chung1, Xiaolin Wang2, Shi Xue Dou2;
1Korea Institute of Materials Science (KIMS), Republic of Korea
; 2Institute for Superconductors and Electronic Materials (ISEM), Australia.
Amorphous boron powders with size of the order of several hundreds nanometers were prepared by self-propagating high temperature synthesis (SHS). The SHS method provides a fast and cost-effective route for fine amorphous boron powders essential to high quality MgB2 wire fabrication. After the combustion reaction of magnesium powders and boron oxide powders at room temperature and subsequent acid leaching, elemental boron powders with high purity (>97%) and very fine particle size distribution (mean diameter < 200nm) were obtained. The prepared boron powders were applied to the powder-in-tube processing for MgB2 wires. The in-situ processed MgB2 wires using SHS-processed fine boron powder shows the clear improvement in microstructures and critical current densities. Also discussed are the effects of various SHS processing conditions such as composition of reactants, pressure, etc. on the microstructures and superconducting properties of in-situ MgB2 wires. This work was partially supported by the Global Partnership Program from the Korea Foundation for International Cooperation of Science & Technology (KICOS) in 2006(M60602000012-06E0200-01210) through a grant provided by the Korean Ministry of Science & Technology (MOST) and partially supported by energy and resource technology development program from the Korea Energy Management Cooporation (KEMCO) through a grant provided by the Korean Ministry of Commerce, Industry and Energy (MOCIE).
3:00 PM *R1-S3.5 (invited)
Doping and Nanotubes Addition Effects on the Superconducting Properties of MgB2. (#898) Adriana Serquis1, German D. Serrano2, Boris Maiorov3, Marcelo Jaime3, Fedor Balakirev3, Gabriela Pasquini4, Alejandro J. Moreno4, Leonardo Civale3;
1Materials Characterization, Instituto Balseiro, Centro Atomico Bariloche, San Carlos de Bariloche, Argentina
; 2Instituto Balseiro - Centro Atomico Bariloche, Argentina
; 3Los Alamos National Laboratory, New Mexico, USA
; 4Universidad de Buenos Aires, Argentina.
One of the most important issues for MgB2 magnet applications is the simultaneous enhancement of its critical current density (Jc) and the upper critical field (Hc2). Thus, on one hand, the pinning force may be improved by the incorporation of defects (nano particle doping, chemical substitutions, etc.). On the other hand, the doping level affects the intraband scattering coefficients and the diffusivity of the two bands of this peculiar superconductor, and these changes may cause a significant Hc2 variation. In particular, we analyze the correlated enhancement of Hc2 and critical current densities Jc obtained by SiC, single or double wall carbon nanotubes and titania nanotubes additions, to understand the role of C substitution and other defects in MgB2 superconducting properties of this material. The microstructure and phase composition of the samples are observed by Scanning Electron Microscopy (SEM) and X-Ray Diffractometry (XRD). Critical temperatures (Tc) and Jc are determined by magnetization and transport measurements. Four-probe transport measurements were performed using a 50 T pulsed magnet to determine Hc2(T). By means of magnetization was also studied the normalized time relaxation rate S=dlnJ/dlnt and pinning energy in the various samples. The different relations between the superconducting properties and the microstructural characteristics are discussed.
3:15 PM R1-S3.6
The Newly Discovered Fe Based Superconductors. (#1470) Xiaolin Wang,
University of Wollongong, Australia.
-
AFTERNOON BREAK 3:30 PM - 4:00 PM
Chair: O. Mukhanov
Monday, July 28, 2008
Level 2 - State Room, Hilton Sydney
4:00 PM *R1-S4.1 (invited)
Effects of Processing Parameters on Superconducting Properties of MgB2 Bulk and Wires. (#828) Chan-Joong Kim,
Neutron Science Division, Korea Atomic Energy Research Institute, Republic of Korea.
Much effort has been made to enhance the critical current density(Jc) of MgB2 superconductor. Characteristics of precursor powders, milling condition of precursor powder, chemical doping level are considered to be important factors in controlling the current carrying capacity of MgB2 at magnetic fields. We investigated material factors and optimum processing condition that can influence the formation of MgB2 superconducting phase and the current properties in in-situ processed MgB2. The highly amorphous boron powder decreased the reaction temperature for the MgB2. Increased grain boundary and defects generated by mechanical milling, and carbon doping also affected the crystallinity, phase homogeneity, and grains size of MgB2, enhancing the Jc at high magnetic fields. This research was supported by a grant (R-2006-1-248) from Electric Power Industry Technology Evaluation & Planning, Republic of Korea.
4:15 PM *R1-S4.2 (invited)
Infiltration of Mg in Porous B Skeletons. (#1015) Jung-Ho Ahn1, Sang Jun Oh1, Xiaolin Wang2, SX Dou2;
1Andong National University, Andong-city, Gyeongsangbuk-do, Republic of Korea
; 2University of Wollongong-ISEM, Australia.
MgB2 have been commonly synthesized either by in-situ or ex-situ methods. However, the resulting materials mostly have a low density with a large number of pores which are detrimental to superconducting properties. Some workers have employed the reactive infiltration of fibrous or porous Mg into B skeletons to obtain highly dense MgB2. However, the microstructures of the infiltrated MgB2 are usually inhomogeneous with persisting residual pores. In the present work, we have examined various factors governing infiltration of Mg into porous B skeletons to obtain homogeneous and highly dense microstructures. The infiltration process could be optimized by a proper control of the capillary size, the addition of a third element, external pressure and atmosphere.
4:30 PM R1-S4.3
Magnesium Diboride Coated Conductors by Screen Printing. (#643) Michael Auinger, Gerhard Gritzner;
Institute for Chemical Technology of Inorganic Materials, Johannes Kepler University Linz, Austria.
Metallic substrates, such as pure iron, copper and titanium were covered with buffer layers by screen printing suspensions of either zirconium dioxide or aluminium oxide in terpineol. After a drying step at 125 ?C, the buffered metal substrates were coated with boron, again applied via screen printing of a suspension of boron in terpineol. The samples were then placed into an aluminium oxide crucible, together with metallic magnesium. Conversion into the superconducting material by vapour phase transfer of magnesium into the boron layer was carried out in an argon-hydrogen (6.5 vol-% H2) atmosphere under ambient pressure at temperatures ranging from 800 ?C to 1 000 ?C. Dense and uniform films were obtained, possessing transition temperatures of up to 38 K and critical current densities of 6 000 A cm-2 at the boiling point of liquid helium. Further characterisation of the tapes was performed by X-Ray diffraction as well as by optical and scanning electron microscopy. Finally, comparison of the superconducting properties of specimens prepared by the screen printing of MgB2 onto buffered metal ribbons with the samples fabricated to the above mentioned technique will be discussed.
4:45 PM R1-S4.4
Fabrication and Superconducting Properties of Mg Diffusion Processed MgB2 Wires. (#1478) Hiroaki Kumakura1, J M Hur1, A Matsumoto1, K Kimura2, H Wada2, K Togano1;
1National Institute for Materials Science, Tsukuba, Japan, Japan
; 2University of Tokyo, Kashiwa, Japan, Japan.
Powder-In-Tube(PIT) method is the most popular method to fabricate MgB2 wires and tapes. However, PIT processed tapes and wires show relatively low Jc values due to the low density of MgB2 cores. Recently, we succeeded in the fabrication of MgB2/Fe wires having high density MgB2 core applying the internal Mg diffusion (IMD) process with pure Mg rod and pure B powder or nano-SiC added B powders. A pure Mg rod with a diameter of 2 mm was placed at the center of a Fe tube with an outer diameter of 6mm and inner diameter of 3.5 mm, and space between the Mg rod and the Fe tube was filled with B powder or B-SiC mixed powder. The composite was successfully cold worked into 0.8 ~ 1.2 mm wire at room temperature without any breakage. The wires were heat treated at 650 ~ 800 oC for 1 ~ 10 hrs under Ar gas atmosphere. During the heat treatment, liquid Mg infiltrated into the B layer and reacted with B to form MgB2. X-ray diffraction analysis indicated that the major phase in the reacted layer is MgB2. SEM analysis of the heat treated wire clearly indicated that the density of MgB2 layer in the wire was higher than that of a PIT processed wire. The Jc at 4.2K of the IMD-processed wire increased with decreasing the heat treatment temperature from 800 oC. Transport Jc values of the SiC added wire heat treated at 670oC reached 1.1 x 105A/cm2 in 8T and 43,000A/cm2 in 10T at 4.2K. These Jc values are much higher than those of usual PIT processed wires. These high Jc values can be attributed to the high density MgB2 layer obtained by this diffusion method. Thus, the densification of MgB2 layer is effective in enhancing Jc of MgB2 wires.
5:00 PM R1-S4.5
Optimized Growth Parameters and Characteristics of Flux Pinning in MOD REBCO Films. (#1286) B Gao1, C B Cai1, Z Y Liu1, Y M Lu1, L L Ying1, F Fan1, T Thersleff2, R Hühne2, B Holzapfel2;
1Department of Physics, Shanghai University, China
; 2IFW Dresden, Germany.
Fabrication of REBa2Cu3O7-x (REBCO, RE=Y, Ho) films using trifluoroacetate (TFA) contained MOD process, including all-TFA and low-TFA methods, is a cost effective method for scale-up to long lengths. Optimizing growth parameters as well as improving flux pinning in MOD-REBCO films have drawn much attention in the area of coated conductors due to the desire of high critical current density (Jc) in self-field and high magnetic fields at the temperature of liquid nitrogen. The phase transformation and optimized growth parameters in the high temperature crystallization process are characterized and studied by X-ray diffraction (XRD), Pole-figure, scanning electron microscopy (SEM) and Inductive measurement of the superconducting properties. It is revealed that the YBCO grains start to form at low temperature 730? during the initial temperature ramp. Higher oxygen pressure and lower growth temperature favor the formation of a-axis grains. And, Low heating rate (3K/min) from 600? to growth temperature does not contribute to the information of a-axis grains, implying important application for thick films. With low oxygen pressure of 100ppm, the optimized growth temperature is reduced to around 780?, at which the films fired shows a Jc value of 3.65MA/cm2, implying great importance to prepare REBCO films on metallic substrate.The investigations on reaction between CeO2 buffer layer and superconducting layer are devoted, using XRD and Focused Ion Beam (FIB). According to comparison of two different buffer architectures (Y2O3/YSZ/CeO2 and La2Zr2O7/CeO2), there is a strong reaction between CeO2 and superconducting layer, which reduces the texture quality of REBCO layer. And this reaction may be influenced by the surfaces roughness of CeO2 layer. Typical MOD pure YBCO films are characterized by a strong pinning in fields oriented in the ab-plane of the YBCO with lower pinning for H//c. A series of mixed rare earth REBCO films, such as Y0.7Ho0.3BCO, YHo0.3BCO etc., are prepared. The Jc values of the YBCO films for H//c in magnetic fields up to 9T are determined by application of the Bean critical state model formula. The characteristics of Jc over the entire range of applied field for all samples are investigated.
5:15 PM R1-S4.6
Research on MOD Processes for YBa2Cu3O7-x Films and Buffer Layers. (#1479) D Q Shi, M Liu, L Wang, Q Li, X B Zhu, J H Kim, R Zeng, S X Dou;
Institute for Superconducting and Electronic Materials, Faculty of Engineering, University of Wollongong, Australia.
The YBCO films with different dopings have been prepared successfully by TFA-MOD method through dissolving dopping chemicals into the precursor solution. YSZ nanoparticles, BaZrO3, and SrZrO3 were detected in doped YBCO films by XRD and SEM. The doped films have better out-plane and in-plane textures than that of undoped YBCO film by the analysis of XRD ω and φ scans. The superconductivity properties of the samples were examined by Quantum Design Magnetic Property Measurement System (MPMS) at different temperatures and under different magnetic fields. High quality YBCO films has been obtained. Although the doped YBCO films have lower Tc than that of undoped YBCO films, a very significant enhancement of Jc is displayed as compared to undoped film at high applied fields. Atomic force microscopy observations revealed that their morphology was very smooth. The surface resistance of YBCO film has been examined.
Chair: Rob Elliman, Laurie Faraone, C. Jagadish, Max Lu, John O'Connor
Monday, July 28, 2008
Level 3 - Grand Ballroom, Hilton Sydney
R1-S5.1
A Study on Densification Behavior and Superconductivity of MgB2 Bulk Fabricated by Spark Plasma Sintering. (#943) Deuk-Kyun Kang, Dong-Woong Kim, Su-Gun Lim, In-Shup Ahn;
Gyeongsang National University, Jinju, Republic of Korea.
A Study on densification behavior and superconductivity of MgB2 bulk fabricated by Spark Plasma Sintering Deuk-Kyun Kang*, Dong-Woong Kim, Su-Gun Lim, In-Shup Ahn Division of Advanced Materials Science and Engineering & K-MEM R&D cluster, Gyeongsang National University, Jinju 660-701, Korea *barybonds@nate.com, sansu81@nate.com, suglim@nongae.gsnu.ac.kr, ais@gnu.ac.kr Keywords: Ball milling, MgB2, Spark Plasma Sintering, superconducting Abstract A number of studies on MgB2 are reported as superconducting materials, because of it's higher critical temperature of 39K than that of other metallic superconductors. As a new sintering process, Spark plasma sintering (SPS) is a rapid heating process with a pulsed electrical discharge that is required to densify powders rapidly without substantial grain growth. The mixed powders for fabrication of MgB2 bulk by SPS were milled-powders for 9 h at Ar atmosphere by planetary ball mill, and by spex mill for 30 min at Ar atmosphere. The properties of Spark Plasma Sintered MgB2 bulk samples were evaluated with XRD, EDS, SEM, PPMS. The relative density of MgB2 bulk samples was increase by increasing temperature. The critical temperature of samples were about 37K.
R1-S5.2
The Fffect of Filament Coupling on AC Losses in Multifilamentary MgB2 Wires. (#407) Serap Safran1, Nusret Güçlü2, Grasso Giovanni3, Íbrahim Belenli4, Ali Gencer1;
1Faculty of Science, Department of Physics, Ankara University, Turkey
; 2Gaziosmanpasha University, Tokat, Turkey
; 3Columbus Superconductors SpA, Genova, Italy
; 4Abant Izzet Baysal University, Bolu, Turkey.
We have measured the fundamental and higher harmonics of ac susceptibility ?=?'-i?'' for the monofilament and multi-filamentary various metal sheated MgB2 wires which are produced by PIT technique. The experimental variables for the measurements of ? were measuring field amplitude, its frequency, dc field and temperature from 15K to 42K. All the ac susceptibility components exhibit field, frequency, and temperature dependences. The ac losses associated with superconducting filament coupling are considered to be hysteretic in nature with frequency independent behavior, while the losses concerning metallic sheathing is dependent on the frequency of the ac field. The effects of filament coupling have been investigated both experimentally and theoretically with numeric simulations of interest and its effect on the ac losses. We compared ac susceptibility curves with the theoretically simulated results based on magnetization equation derived by various models in cases where analytic solutions to governing equations are impossible. Our model computations by the personnel computer software, which. will be presented in detail and be compared with literature. In addition a novel technique will be provided to determined irreversibility line in such wires and tapes.
R1-S5.3
Effect of Ball Milling on the Superconductivity of MgB2 Wire. (#1007) Dong-Woong Kim, Deuk-Kyun Kang, Su-Gun Lim, In-Shup Ahn;
Many studies on the MgB2 are reported for superconducting materials due to high critical temperature (39K) among metallic superconductor and easy forming. In this study the effects of milling velocity, milling time and annealing temperature on the MgB2 phase formation and the superconductivity of MgB2 wire were investigated the mixture (pure Mg and B = 1:2) powder and pure B powder has been milled by using ball mill. To evaluate the superconducting characteristics, the MgB2 wire was fabricated with drawing in Fe sheath materials (purity = 99.5%) by the powder in tube method (PIT) using MgB2 powder. Then the fabricated wire was annealed under argon atmosphere. The properties of milled powders and the fabricated MgB2 wire were evaluated with X - Ray Diffraction (XRD), Transmission Electron Microscope (TEM), Scanning Electron Microscope (SEM) and Physical Property Measurement System (PPMS). The relative density of MgB2 wires was over 96% and the mean grain size of MgB2 powder was about 1um. The transport critical current (Ic) was measured for Fe sheathed MgB2 round wires. A critical current density of 5.33 A/cm2 was obtained at 32 K.
R1-S5.4
Magnetic Properties of Metal Oxides Doped YBCO Ceramics. (#375) Sang Heon Lee, Yong Choi;
Sun Moon University, Republic of Korea.
The CeO2 doped YBCO superconductor were prepared by the partial melt process involving the peritectic reaction, to investigate the effect of the dopant on microstructure and superconductivity. All the doped CeO2 could be successively separated from 123 phase by applying the partial melt process. The separation of the dopant from the superconducting phase resulted in the constant Tc regardless of CeO2 content. The CeO2 was converted to fine BaCeO3 particles which were trapped in 123 matrix during the peritectic reaction. Electromagnetic properties of CeO2 doped and undoped YBaCuO superconductor were evaluated to investigate the effect of pinning center on the magnetization properties. It was confirmed experimentally that a large amount of magnetic flux was trapped in the CeO2 doped sample than that in the undoped one, indicating that the pinning centers of magnetic flux are related closely to the occurrence mechanism of the magnetic effect.
R1-S5.6
Synthesis and Analysis of MgB2 Thin Films by Co-Evaporation Method. (#1044) Sung Chang Park, Jun-Ki Chung, Seong Gu Kang, Chan-Joong Kim, Cheol Jin Kim;
i-Cube Center and Advanced Material Research Center, Division of Nano & Advanced Materials Science and Engineering, Gyeongsang National University, Jinju, Republic of Korea.
MgB2 thin films have been synthesized under a variety of conditions. Controlling the substrate temperatures, deposition rates, and deposition times, we could have grown MgB2 thin films on sapphire (Al2O3) substrate. Before the co-evaporation of Mg and B, the deposition rates of each element have been measured separately. While the substrate temperature increased above the optimum growth condition, Mg started to evaporate from the already reacted MgB2 and form MgB12 as a second phase. As second phase was increased, critical temperature tended to be decreased. Superconducting properties have been measured by PPMS and the microstructural features have been characterized with XRD, FE-SEM and TEM.
R1-S5.7
Temperature Effect on Performance of Polycarbosilane and Sugar Doped MgB2 Wires. (#742) A. V. Shcherbakov, J. Horvat, O. V. Shcherbakova, J. L. Wang, S. X. Dou, M. Jercinovic, E. Babic;
Institute for Superconducting and Electronic Materials, The University of Wollongong, New South Wales, Australia.
Effect of processing temperature on structure and superconducting properties of polycarbosilane (or PCS, C2H6Si) and sugar (C6H12O6) doped MgB2 wires has been investigated. It has been observed that increasing of sintering temperature from 650 to 950 0C results in higher level of C substitution on B sites in the MgB2 crystal lattice, and it is large in sugar doped than in PCS doped samples. For both dopants studied, the in-field Jc(Ba) behaviour is enhanced as processing temperature increased. The improvement of in-field Jc performance in both doped samples is due to stronger pinning on lattice defects caused by C substitution into the MgB2 crystal lattice. In spite of the fact that the level of C in the crystal lattice is higher in the sugar doped MgB2 sample, this sample has lower Jc(Ba) when compared to the sample with PCS addition. We speculate that it is due to higher level of MgO impurities in the sugar doped sample (18.6 wt. % compared to 9.15 wt. % in the PCS doped sample), which result in dissipation of supercurrent flowing through this sample. In addition, a higher processing temperature led to the enhancement of Bc2 values in both PCS and sugar doped samples. In contrast to observed Jc(Ba) behaviour in the samples studied, the upper critical field value correlates with the level of C substitution in the MgB2 lattice, i.e. Bc2(T) is higher for the sugar doped sample when compared to the sample with PCS doping. This difference becomes even more pronounced at low measuring temperatures (as T &rarr 0 K).
R1-S5.8
Transport and Magnetic Critical Current in Two Sintering Step of In Situ MgB2/Fe Wire. (#922) Xun Xu1, J. H. Kim1, Shixue Dou1, W. K. Yeoh1, S. Choi2, T. Kiyoshi2;
1Institute for Superconducting and Electronic Materials, The University of Wollongong, New South Wales, Australia
; 2National Institute for Materials Science, Japan.
A two-step process was used in order to improve the critical current density (Jc) of in situ MgB2/Fe wires. MgB2/Fe wires were first drawn the outer diameter from 10.11mm to 7.80 mm , and annealing at 550 Celsius degree for 30 mins flowing Ar gas, then final drawing to 1.42mm, and sintering at 700 Celsius degree for 30 mins flowing Ar gas also. Compare to the one step sintering sample as reference, it is very interesting that the magnetic critical current (Jcm) is slightly increasing at 8T, 5K, but the transport critical current (Jct) of tow-step sintering sample is decreasing in orderliness from 4T to 12T under 5K. At the same time the critical temperature (Tc ) is also dropping down. It is thought that the reason is not only by the different measurement error, also by the impurity phase effect , such as increased the MgO content in two step processing to block the current. Also, in this case, just used the magnetic critical current to estimate the sample superconductor propriety is enough or not must be review.
R1-S5.9
Significant Improvement of Jc in MgB2 Bulks Superconductor by Ball-Milled High-Purity Crystalline Boron. (#677) Yun Zhang, Xun Xu, Sihai Zhou, Yue Zhao, Jung Ho Kim, Shi Xue Dou;
Institute for Superconducting and Electronic Materials, The University of Wollongong, New South Wales, Australia.
In this paper, the ball-milled crystalline boron (BMCB) powder was used to make MgB2 bulks. The samples were sintered at temperature range from 650?C to 1050 ?C. The superconducting properties of MgB2 made with this BMCB powder were studied. Jc of the 650 ?C sintered MgB2 was estimated to be 9x103Acm-2 at 8T and 5K. This value is two times higher than that of MgB2 made with ball-milled amorphous Boron (BMAB), and a factor of 40 higher than that of MgB2 made from amorphous Boron without ball-milling. It was suggest that the small grain size of samples caused by ball-milling is effective for enhancing flux pinning at the grain boundaries, which represent effective pinning centers. SEM images show the good connectivity in the samples of BMCB sintered at 850oC, resulting in the best Jc (B) performance under high field.
R1-S5.11
Effect of Multi-Spin Co Doping on M-I Transition in La2/3Ca1/3MnO3 Manganites. (#312) Quanying Yu, Miaoqin Chen, Jincang Zhang, Dongmei Deng, Shixun Cao;
Department of Physics, Shanghai University, China.
It is well known that the transport and magnetic properties of R1-xAxMnO3 have strong dependence on doping level, for instance, in La1-xCaxMnO3 the simultaneous occurrence of metallicity and ferromagnetism for intermediate doping level 0.2 R1-S5.12 We report on fabrication and characteristics of ferromagnetic GaCrN thin film on a GaN/sapphire (0001) substrate by employing novel feasible hybrid physical-chemical vapor deposition. GaCrN film shows a typical ferromagnetic hysteresis loop at 300K implying that room temperature ferromagnetic ordering exists in the presently synthesized GaCrN film. High resolution x-ray diffraction spectra shows that crystallinity of GaCrN film is similar to that of undoped GaN film without forming CrxNy or CrxGay compounds. Besides, X-ray photoelectron spectroscopy (XPS) spectra confirm that Cr atoms dissolve to form a good solid solution in GaN matrix. According to those analysis results, it is concluded that GaCrN film fabricated by hybrid physical-chemical vapor deposition employed in the present work is a promising material for spintronics devices such as spin-field effect transistors (spin-FETs) and ultradense nonvolatile semiconductor memory (MRAM). R1-S5.13 The magnetic metal nanowires with single crystal structure have attracted much attention in recent years due to their potential application for the highly magnetic density storage. Usually, the magnetic metal nanowires with single structure are achieved by depositing the magnetic metals into the anodic alumina membrane (AAM) with a nanosized porous array. It has been generally regarded that the magnetic metal nanowire grows along the easy magnetization direction being parallel to the nanowire direction, and hence resulting in the high magnetic anisotropy. In the present paper, however, we argue that the magnetic metal nanowire grows not along its easy magnetization direction, but along its preferred crystallographic orientations, which can also lead to the high magnetic anisotropy. We prepared the highly ordered Ni nanowires by electric-chemical deposition method in the AAM templates. The observation of high resolution transmission electron microscope (HRTEM) shows that the Ni nanowire grows along its preferred crystallographic orientation [002] by rotating the nanosized crystals to form a single crystal with a compact structure. All the samples show the high magnetic anisotropy. We attribute such a magnetic anisotropy mainly to the nano-shape effect rather than the easy magnetization direction. Clearly, our results show the direct evidence for the growth direction of magnetic metal nanowires, which may provide a new insight into developing highly magnetic density storage. R1-S5.14 Electron beam lithography is an easy way to manipulate materials at nanometer scale. A zwitterresist refers to a resist which depending on the applied doses can exhibit both positive and negative properties. Resists with simultaneous positive and negative patterning capabilities are beneficial to the electron beam direct writing technology. Conventional developers are typically volatile and toxic: posing health hazards and contributing to environmental pollution. The developers also increase the overall costs of lithography processing. Recently, many environmentally friendly lithographic processes have been designed to use either water based solutions or supercritical carbon dioxide in developing resists.
Partially substituting the La3+ in functional ceramics such as LaMnO3 with divalent ions like Sr2+ or Ca2+ generates a number of spectacular properties. Most significantly is the production of colossal magnetoresistance (CMR) of these manganese oxide materials which is currently under tremendous investigation. Manganite thin films possessing CMR have many potential applications including field sensors and recording devices.
In this experiment, the electron beam resist was prepared by dissolving 4.50 wt% of lanthanum nitrate (La(NO3)3.6H2O, Acros, 98 %), strontium hydroxide (Sr(NO3)2, Riedel-dehaen, p.a.), manganese nitrates (Mn(NO3)2.4H2O, Fluka, >97 %) and 1.70 wt% polyvinyl alcohol (Acros, 88 %, 22000 g/mol) in water with a molar ratio of La:Sr:Mn=0.7:0.3:1. The solution was stirred for 48 hours at 25oC. Then the LSMO material was spin coated at 3000 rpm for 90 seconds to give a nominal thickness of about 180 nm. High-resolution nanolithography was performed by writing specific patterns across the 150 um field with a 2.5 nm beam step size using a Hitachi ELS-7500EX machine operating at 100 kV with a probe current of 1.0 nA. A sample containing a 3 x 3 array of field was exposed with a start dose of 1us then with an additional dose increment of 0.01, 0.1 and 1us per field, respectively. The exposed sample was then developed with pure water for 30 seconds.
The water developable La0.7Sr0.3MnO3 electron beam resist exhibits dual negative patterning and positive patterning functions depending on the electron beam dosage. We have previously illustrated that the formation of La0.7Sr0.3MnO3 resist pattern is due to the heating from the electron beam exposure. Herein, we measure the surface potential of different La0.7Sr0.3MnO3 patterns by Kelvin probe force microscopy (KFM) to confirm the formation of La0.7Sr0.3MnO3 resist pattern. KFM has been widely used for nanoscale mapping of work function differences. These resist can be developed in a nontoxic and environmentally friendly manner using pure water. The formation of the periodic magnetic structure has been verified using a magnetic force microscope. Our approach provides a simple and convenient route for the fabrication of nano-scale magnetic patterns, which serve as the building blocks in the search for novel properties of periodic magnetic arrays, such as magnetic photonic crystals. R1-S5.15 Yongsheng LIU1) *, Yunbo ZHONG2), Jincang ZHANG3), and Zhongming REN2)
1) Department of Mathematics and Physics, Shanghai University of Electric Power, Shanghai 200090, China
2) Department of Materials Science & Engineering, Shanghai University, Shanghai 200444, China
3) Department of Physics, Shanghai University, Shanghai 200444, China
Recently, many researchers have mainly focused their efforts on the physics of magnetic field-induced transition, one of the most interesting problems in condensed matter physics and materials science. As representatives of soft magnetic ferrites, MnZn ferrites are important to industry because of their dielectric and magnetic properties, so their physical properties have been investigated extensively.
In this work, nanocrystalline Mn0.6Zn0.4Fe2O4 particles are synthesized by a phase transformation method under the magnetic field of 0 and 6 T, respectively. Under 6 T, the particles agglomerate together like colloidal with a narrow size distribution. The majority of the 6 T nanoparticles are superparamagnetic from ~45 to ~300 K. Interestingly, the saturation magnetization of the 6 T sample is ~18 % and ~16 % higher than that of the 0 T sample at 120 K and 300 K, respectively. The magnetic field may have some effects on the morphology, the grain size, the surface anisotropy and the ion (atom) distribution, which results from suppression of the convection and the movement of matter by the Lorentz force and the magnetization force. Considering that the saturation magnetization is an important parameter for soft magnetic materials, the technique outlined here, promises to be an important approach in enhancing the saturation magnetization of nanoparticle ferrites with a narrow size distribution.
*Corresponding author: e-mail: yongshengliu@sina.com
This work is supported by NNSFC (Nos.50404018, 50234020), STCSM (Nos. 0752nm012, 07QA14026, 071605123), FNEDAEDT (No.200235), and SHMEC (No.06LZ011). R1-S5.16 Dieter Lott 1; Jochen Fenske 1, Frank Klose 2,3; Gary J. Mankey 4; Wolfgang Schmidt 5; Prakash Mani 4; Andreas Schreyer 1¶
1 GKSS research center, Max-Planck Str. 1, 21502 Geesthacht, Germany¶
2 ANSTO, Bragg Institute, Menai, NSW, 2234, Australia¶
3 Spallation Neutron Source, Oak Ridge National Laboratory,Oak Ridge, TN, USA¶
4 MINT Center, The University of Alabama, Tuscaloosa, AL, USA¶
5 Research Center Juelich, D-52425 Juelich , Germany¶
¶
For a few years perpendicular recording media are used to overcome the restrictions of the longitudinal recording media due to the superparamagnetic limit. In order to further increase the storage density, the search for new materials with higher magnetic anisotropies is still ongoing. Here, FePt is a very promising candidate due to its extremely high magnetic anisotropy which enables one to increase the storage density and its capacity to more than 1 Tbit/in2. However, the high anisotropy is also associated with restrictive requirements concerning i.e. the very high write field. To lower it to a feasible field range of around 1 Tesla magnetic underlayers are used acting as a magnetic mirror. Possible candidates for such an underlayer for FePt systems are L10 structured Fe(50)Pt(50-x)Rh(x) alloys due to their perfect lattice match. The bulk system shows for a Rh concentration of around x=10 an antiferromagnetic (AF) phase at low temperature and ferromagnetic (FM) phase at high temperature [1]. In comparison with conventional underlayers it allows in principle not only to strongly reduce the write field but also to stabilize the magnetization state of the recording media by switching between the FM and AF state, respectively. However, considering material costs and fabrication time, thin films are important for its application. ¶ In this work thin films of the L10 structured Fe(50)Pt(50-x)Rh(x) alloys are investigated by unpolarized and polarized neutron diffraction and refined by structure calculations. A detailed picture of the magnetic configuration could be developed showing significant differences to the bulk properties. The intriguing behavior of the magnetic configuration demonstrates that the magnetic properties of the Fe(50)Pt(50-x)Rh(x) alloy depend not only strongly on the Rh concentration but also on the thickness of the sample. This may open up new ways to modify the magnetic properties for future applications.
¶
[1] Takizawa, K; Ono, T; Miyajima, H, Journal of Magnetism and Magnetic Materials 226: 572 Part 1 Sp. Iss. SI MAY 2001 R1-S5.17 Rare Earth Giant Magnetostrictive Materials (GMM) have become the novel strategic functional materials since 1970s. The magnetostrictions of GMM under a Low-field drive are as large as 2000ppm. As compared with traditional magnetostrictive materials, GMMs exhibit many excellent properties, such as, large magnetostriction, outstanding energy density, fast response, low voltage drive, large coupling coefficient, etc. GMM has wide application in aerospace, medicine, agriculture, electronics, naval and petroleum industries.
GMM can be produced by directional solidification techniques and bonding method. Oriented GMM rods are mainly produced by directional solidification techniques which are considered to be inherently difficult, and hence expensive, due to the need of precisely controlling multiple growth parameters. More importantly, the eddy current loss under a high-frequency drive is the major inhibitors to their applications due to the low resistivity. To overcome this problem, polymer-bonding technology was considered. With the inclusion of polymer binder with a high electrical resistivity, the frequency limit of GMM can be greatly improved. Unfortunately, the magnetostriction of bonded GMM was reduced due to the dilution effect with the presence of a non-magnetic polymer binder. A large amount of experimental and theoretical analyses were conducted by scanning electron microscopy (SEM), X-ray diffraction analysis (XRD), and Orientation Distribution Function analysis (ODF).The influences of the particle size, proportion of binder and compaction technics on the properties: density, resistivity, magnetostriction, power consumption and the texture of the bonded GMM have been investigated. The experiments were carried out in various conditions, including particle size, compaction pressure and binder proportion in order to optimize the preparation method. The large magnetostrictions of 1020 ppm for the bonded GMM with an applied compressive stress of 5MPa have been obtained (E-12) with the following conditions: particle size of 50~80?m, weight ratio of epoxy resin binder to alloy powder of 3:100, weight ratio of silane (KH550) to alloy powder of 0.8:100, compaction pressure of 110MPa under an applied vertical magnetic field of 2T, Cold Isostatic Compression (CIP) of 200MPa.The results of ODF analysis showed that bonded GMM mainly obtained <113> and <112>textures. R1-S5.18 From a structural viewpoint, superlattices can be classified into two types. The first is the epitaxial superlattice, in which alternating layers with a small lattice mismatch between them are epitaxially grown. Most semiconductor superlattices belong to this category. The other is the non-epitaxial superlattice in which each layer has a different structure, for example a polycrystalline/amorphous superlattice. In order to effectively induce quantum effects in superlattices, the former is ideal. However, it is limited to combinations that afford alternate epitaxial growth. For the non-epitaxial superlattices, the quantum effects due to the layered structure can be enhanced by the suitable orientation of the crystalline planes. One of the representative quantum effects is the interlayer coupling induced between ferromagnetic layers separated by nonmagnetic spacer layers. It has been investigated to a significant extent since it can cause the spin-dependent scattering of conduction carriers, which is exploited for giant magnetoresistance effects. In our previous study on Fe3Si/FeSi2 superlattices deposited at room temperature (RT) [1], it was found that the crystalline orientation of the Fe3Si layers is indispensable for the antiferromagnetic interlayer coupling induction.
[Fe3Si (25 Å)/FeSi2 (X Å)] superlattices were prepared on Si (111) at different substrate temperatures of room temperature and 300°C by facing target direct-current sputtering. Here, X is an FeSi2 layer thickness estimated from the deposition rate and time and it was changed up to 100 Å. The transmission electron microscopy and X-ray diffraction measurements showed that Fe3Si layers were epitaxially grown from the first layer on Si (111) to the final layer across the amorphous-like FeSi2 layers. While this unique epitaxy occurs at the limited FeSi2 thicknesses X ≤ 17.5 Å, it was realized at the thicknesses up to X = 100 Å for those deposited 300°C.
[1] K. TAKEDA, T. YOSHITAKE, D. NAKAGAUCHI, T. OGAWA, D. HARA, M. ITAKURA, N. KUWANO, Y. TOMOKIYO, T. KAJIWARA, and K. NAGAYAMA, Jpn. J. Appl. Phys. 46 (2007) pp. 7846-7848. R1-S5.19 This work describes the structural and properties of rare earths doped bismuth titanate using a wet chemical technique. Bismuth titanate is a promising material for ferroelectric random access memories (FeRAM) and antenna applications due to its excellent ferroelectric properties. However, its ferroelectric properties are not as good as hazardous PbZrxTi1-xO3. Therefore, in this study, rare earth elements such as prasedymium (Pr) and lanthanum (La) are introduced in bismuth titanate to overcome the deficiency of ferroelectric properties. Nitrate based bismuth and rare earth are dissolved in 2-methoxyethanol, while titanium isopropoxide is dissolved separately in 2-methoxyethanol and acetylacetone. After that, the solutions are mixed and are continuously stirred for two hours at room temperature. The solution is then heated up to obtain a powder. Nano size powder is obtained after the solution undergoes a soft combustion process. X-ray diffraction analysis shows that the powder produced by this technique is in crystalline structure but it contains some impurity phases. A single phase compound is obtained after post heat treatment process at 800?C. Dielectric properties are studied on sintered pellet with varying sintering temperatures and rare earth compositions at low and high frequencies. Dielectric properties study shows that only a certain amount of rare earth elements is beneficial to improve bismuth titanate properties at low and high frequencies. Scanning electron micrographs of the fractured sintered pellets show that all compositions consist of plate-like structure. R1-S5.20 The Effects of Oxygen Partial Pressure and Flux Content on Multiferroic BiFeO3 Thin Films Growth via Flux-mediated Epitaxy
C.-J. Cheng, V. Anbusathaiah , V, Nagarajan
School of Materials Science and Engineering, University of New South Wales, NSW 2052, AUSTRALIA
S.-H Lim, M. MurakamiI, I.Takeuchi
Department of Materials Science and Engineering, University of Maryland, College Park, Maryland 20742, USA
Flux-mediated epitaxial (FME) of functional oxides have recently been reported for developing thin films with high level of single crystal quality. Here, we have successfully deposited multiferroic BiFeO3 (BFO) thin films onto (001) oriented SrTiO3 substrates by FME technique using pulsed laser deposition (PLD) with various top and seed BFO oxygen partial pressure and flux (Bi2O3-CuO) content. Transmission electron microscopy (TEM) studies showed all FME grown BFO films have exhibited epitaxial growth with excellent crystallinity. Moreover, in comparison to standard PLD technique, dielectric constant has trebled and leakage current density has improved by two orders of magnitude. Piezoelectric force microscopy (PFM) experiments indicated switching does not impinge on the flux content and low oxygen partial pressure of 3mTorr during film growth proves to be an important factor for the formation of secondary phase.
Research at UNSW was supported by an ARC Discovery Project DP0666231 and a DEST ISL grant. Work at Maryland was supported by access to the Shared Experimental Facilities of the UMD-NSF-MRSEC (DMR 0520471), NSF DMR 0603644, and ARO W911NF-07-1-0410. The work was also supported by the W. M. Keck Foundation and NEDO. R1-S5.21 Recently, semiconducting MoO3 film has strongly attracted attention as a conductance-type gas sensor because of high sensitivity to various gases such as NOx, CO, H2, and NH3 in the temperature range of 300-600oC. There are diverse deposition techniques for MoO3 film such as thermal evaporation, sputtering, chemical vapor depositio, electrodeposition, and flash evaporation. The characteristics of the films are dominated by deposition technique and its parameters, so that a challenge of new approach is required as well as extensive studies of structural and physical properties to obtain enhanced sensing properties. In this study, a new fabrication technique of MoO3 film for a gas sensor, which is accomplished by chemical vapor transport of MoO3(OH)2 during hydrogen reduction of MoO3 powder, is suggested. MoO2 film was deposited at 550oC in H2 atmosphere and the deposited film was oxidized at 600oC in air environment to fabricate MoO3 phase. Electrical properties and gas sensing characteristics of the films were discussed relating with microstructural evaluations. R1-S5.22 Single NV centres in diamond have been the subject of many studies in recent years due to their potential applications in quantum information processing. Compared to other single photon sources such as attenuated lasers, single atoms, molecules and semiconductor quantum dots, the NV diamond colour centre has the advantage of simplicity, photo-stability and room temperature operation. Despite these excellent properties, a recipe for maximizing the efficiency of NV production is yet to be optimized. This study is a step towards this optimization and uses photoluminescence and confocal fluorescence spectroscopy to investigate the NV yield of high purity single crystal type IIa diamond samples implanted with nitrogen followed by thermal annealing. The parameters varied include implanted nitrogen species, implantation energy, temperature, fluence and annealing temperature. Further, the study distinguishes between the yields of NV- and NVo and offers theoretical basis for the observed differences. R1-S5.23 Al adulterated Ta-Al-N thin-films and Cu/Ta-Al-N/Si multilayer were prepared by RF reactive magnetron co-sputtering method. Then the samples were annealed at temperatures varied from 300? to 900? for 300s in N2 protection amibent. Four-point probe(FPP)sheet resistance measurement, Alpha-Step IQ Profilers, Atomic force microscope (AFM), Scanning electron microscope(SEM) and Energy dispersion Spectrometer (EDS), X-ray Diffraction(XRD) were used to characterize the film properties. The results show that with the deposition power of Al target increase, the surface Root-mean-square(RMS) decline, sheet-resistance increase, the barrier properties and adhesion with copper improved. Ta-Al-N(50nm) thin-films with the Al deposition power of 120W can effectively prevent Cu agglomeration after annealing at 800? for 300s, the barrier properties and thermal stability of Ta-Al-N thin-films is thus superior than that of Ta-N thin-films because of Al atoms stuffed the grain boundaries and defects in the barrier. After higher temperature annealing, Cu diffuse through the barrier, the appearance of Cu-Si and Ta-Si compounds indicated the failure of the barrier.
Key words: Ta-Al-N thin-films; barrier properties; Cu diffusion; annealing R1-S5.24 MgB2 films were synthesized using ultrasonic spray pyrolysis (USP) technique followed by a post-annealing process without excessive magnesium addition. The MgB2 films were deposited on c-Al2O3 substrates at various deposition temperatures. The feed solution was prepared by dissolving the correct amounts of Boric acid and Magnesium acetate tetrahydrate into distillated water and ethanol solution and the overall concentration were fixed at 0.1 mol/L. During the decomposition, 96% Ar - 4% H2 was used as carrier gas. The influence of the temperature, such as substrate temperature and post-deposition annealing, on composition, structural, and electrical properties of MgB2 films was investigated. The MgB2 films were characterized by X-ray diffraction, scanning electron microscopy, and physical property measurement system. R1-S5.25 Thermodynamic, transport and magnetotransport properties of free charge carriers in the diluted magnetic semiconductor with a quantum well InGaAs in the GaAs with ?-doped by C and Mn are investigated. The thermodynamic model have been formulated, and the exact analytical expressions for the thermodynamic characteristics of the system with intermediate Fermi-Boltsman statistics have been received. For definition of hole density in the quantum well thermodynamic calculations of the composition of the system from free holes, atoms and ions Mn- have been carried out. Calculations of temperature dependence of resistance and magnetoresistance of free holes in quantum well have been obtained. The contributions of various hole scattering mechanisms in resistance are analysed. The reasons for occurrence of negative magnetoresistance are explained quantitatively as the reduction of the spin-flip scattering by aligning spins by magnetic field. R1-S5.27 Some batches of Bi- based superconducting samples were prepared by solid state reaction method. The batch of sample Bi1.5-Pb0.5-Sb-Sr2-Ca2-Cu3O? was prepared with the addition of Sb. The Tc (zero)was found near 158K by electrical resistivity measurements. The observations showed that the addition of Sb in proper stoichiometric ratios helped in the enhancement of zero resistance Tc. R1-S5.28 There has been a lot of interest in the development of nonvolatile memories based on ferroelectric materials. For the NDRO-FRAM(nondestructive read-out ferroelectric random access memory), a ferroelectric gate structure is required. However it is still difficult to obtain a good quality of ferroelectric thin film on the Si surface. Thus, a buffer layer with a high dielectric constant is often inserted between the ferroelectric film and Si substrate. In this paper, it will be discussed the characteristics of the MFIS structure composed of a ferroelectric PVDF-TrFE(75/25) film and LaZrOx film as a buffer layer on the Si(100) substrate to reduce the leakage current.
The LaZrOx films were deposited by a sol-gel method. After the deposition, The LaZrOx films were crystallized at 750 oC for 30 minutes in O2 ambient. PVDF-TrFE(75/25) films were deposited on these LaZrOx/Si structures using a sol-gel technique. The sol-gel solution was spin-coated on LaZrOx/Si structures at 500 rpm for 5 sec and 2500 rpm for 15 sec. The deposited layer was dried at 165 oC for 30 min in air on a hot-plate. Then, we deposited Au electrode on PVDF-TrFE films using thermal evaporation.
The memory windows width of the MFIS structure increased 0.3 V to 2.3 V, as the bias voltage increased 1 V to 5 V in the C-V curves of the Au/PVDF-TrFE/LaZrOx/Si structure. The leakage current density values at 10 V are about 6.4x10-7A/cm2 in the I-V curves of the MFIS structure. The electrical and crystalline properties of the MFIS structure will be discussed in detail. R1-S5.29 PVDF (polyvinylidene) and its copolymer TrFE (fluride-trifluorethylene) are representative ferroelectric polymers, because of the unique mechanism of their ferroelectricity. And they have been applied to soft transducers, FeRAMs (ferroelectric random access memories) and so on.
The original plan, we attempted to fabricate MFS-FETs structure (metal-ferroelectric-semiconductor field effect transistors) on the silicon. However, owing to the leakage current of the between PVDF-TrFE and silicon, we inserted the buffer layer between PVDF-TrFE film and silicon. In this structure, however, such new problems arised that the data retention characteristics was degraded because of the generation of depolarization field in the ferroelectric film and the increase of the operation voltage. In order to solve the problems, it was important to increase the buffer layer capacitance. At the same time, to decrease the leakage current. ZrO2 films have been studied widely for gate oxides due to their high dielectric constant, relatively large band gap, good thermal stability with silicon.
A MFIS (metal-ferroelectric-insulator-semiconductor) structure's capacitor was fabricated using a ZrO2 buffer layer and a PVDF-TrFE ferroelectric film. The ZrO2 film was prepared by sol-gel method and PVDF-TrFE film was deposited by sol-gel method. The memory window width of this film was about 2.0V with a voltage sweep of ?7V. In this structure, the value of the leakage current density was lower than 1 x 10-7A/cm2 at 5V. Based on these results, we fabricated a MFIS-FETs structure. The memory window width in the drain current-gate voltage curve of the MFIS-FET was about 2.5V. R1-S5.30 Abstract There is widespread understanding that high temperature superconductor (HTS) wires are the best opportunity to improve the electric power grid, transportation, telecommunication and many other industries. In order to employ the so-called Coated Conductors - superconducting wires based on thin film technology the total critical current density of the wires has to be enhanced. However, the critical current density (Jc) of the films is well known to degrade with increasing thickness (dp) of the films as Jc - 1/dp. This inverse dependence of the Jc on their thickness is the result of serious microstructure degradation with increasing thickness of films.
High temperature superconductors as YBCO films are deposited in the form of ReBCO superconducting multilayers (where Re is a rare earth element). The metallic rolled strip with ISD buffer layer was used as a substrate material. Samples were observed with the help of scanning electron microscopy (SEM). The Jc enhancement is observed in entire magnetic field range, which attributed to denser surface morphology of the multilayer, better grain alignment and additional formation of dislocations at the interfaces between the layers. R1-S5.31 Tunable dielectric thin films have been widely investigated for microwave tunable device applications, such as phase shifters, tunable filters, varactors etc. Low dielectric loss, high tunability and reasonable dielectric constant are required for such applications. Many efforts have been made to meet above requirements. A composite structure is one of the effective approaches. A composite film is composed of different compositions and provides an opportunity to tailor and optimize the properties of the dielectric films. Recently, cubic Bi1.5ZnNb1.5O7 (BZN) pyrochlore dielectric has been found to be dielectric-tunable by an electric field. The BZN exhibits very low dielectric loss and moderate dielectric constant. Meanwhile, barium strontium titanate (BST) thin films have been intensively studied for tunable devices due to their high dielectric tunability. It is expected that introducing BZN in BST films to form BST/BZN composite films will reduce dielectric loss and dielectric constant of BST films and meanwhile keep high tunability. This talk will report on the fabrication, structures, dielectric properties and tunability of the BZN based composite thin films. Several novel composite approaches have been investigated to enhance tunability and figure of merit. The dielectric relaxation and dielectric tunable behavior will be discussed. 11:00 AM *R2-S2.1 (invited) In recent years, a new class of magnetoelectric multiferroics such as TbMnO3 and Ni3 V2 O8 has been discovered [1]. In these systems, ferroelectric order develops upon a magnetic phase transition into a spiral magnetic ordered phase. Thus, the noncollinear spiral magnetism is the key to understanding the ferroelectric and magnetoelectric properties in these systems. In spiral magnets, inversion symmetry is broken owing to magnetic order, and some spiral-ordered structures such as a cycloidal one make the system polar. This means that a magnetic order can induce ferroelectricity. The ferroelectricity in the new class of magnetoelectric multiferroics can be explained in terms of this scheme. Because spiral order often arises from the competition between nearest-neighbor and further-neighbor magnetic interactions, systems containing competing magnetic interactions (spin frustration) are promising candidates for magnetoelectric multiferroics. Thus, it is no longer so difficult to find new magnetoelectric multiferroics. Indeed, on the basis of this strategy several new magnetoelectric multiferroics related to spiral magnetic orders have been discovered in the past few years. However, most of them operate only at low temperatures (<40 K). This is mainly because competing magnetic interactions that play a role in producing spiral magnetic structures often reduce the magnetic ordering temperature. In this talk, I discuss a trial to develop new magnetoelectric multiferroics, in particular at high temperatures.
This work has been done in collaboration with H. Nakamura, Y. Sekio, S. Danjoh, K. Kimura, T. Siegrist, and A. P. Ramirez.
[1] T. Kimura, Annu. Rev. Mater. Res. 37, 387 (2007). 11:15 AM *R2-S2.2 (invited) Understanding the mechanism of ferromagnetism in transition metal-doped wide band gap ZnO and TiO2 is one of the most challenging problems of the last decade in magnetic materials physics. Conventional models of ferromagnetism in oxides do not apply and charge-mediated models, commonly referred to in the literature are not applicable to these materials with high Curie temperatures, dopant concentrations well below the percolation threshold and often exhibiting highly insulating behavior. Our results point to a novel ferromagnetism associated with crystal defects [1,2]. Studies directed at precise understanding of the atomic nature of the defects, other than the transition-metal dopants, involved and how they give rise to ferromagnetism are presented here.
We have prepared high-quality, epitaxial, Co0.03Ti0.97O2 (anatase) thin films and confirmed that Co is not metallic but in the +2 state and is uniformly distributed (no granularity) in the films. Using complementary experiments we confirmed that the room temperature ferromagnetism observed in these films is not carrier mediated, but co-exists with the dielectric state [1]. Further, combining Z-contrast imaging with atomic column-by-column electron-energy-loss spectroscopy (EELS) we show that they contain arrays of Co-Ti+3-VO defect complexes in which Co atoms occupy select interstitial sites. These defects are seen only in annealed samples that are ferromagnetic at room temperature. First-principles, spin-polarized density-functional calculations confirm that, under the pertinent experimental conditions, interstitial Co is energetically preferred over substitutional Co and its energy is lowest at the observed sites, that an O vacancy binds to the interstitial Co to form a Co- Ti+3-VO complex and that this complex has a magnetic moment in agreement with the measured value. Spin-aligning interactions appear to be sufficiently strong even in the dilute limit to account for ferromagnetic ordering [2,3].
[1] K.A. Griffin, A.B. Pakhomov, C.M. Wang, S.M. Heald, Kannan M. Krishnan, Phys. Rev. Lett., 94, 157204 (2005)
[2] K. Griffin Roberts, M. Varela, S. Rakshev, S. Pantelides, S. J. Pennycook and Kannan M. Krishnan, Phys, Rev. Lett. (under review)
[3] This work was supported by NSF/ECS 0224138 and by the Campbell Endowment at UW. 11:30 AM *R2-S2.3 (invited) We have investigated two types of bilayered multiferroic structure, namely BiFeO3 buffered by SrRuO3 and BiFeO3/CoFe2O4, both of which are deposited on Pt/TiO2/SiO2/Si substrates. The SrRuO3 buffer layer promotes crystallization and formation of the perovskite phase at lowered temperature. It significantly reduces the leakage current of multiferroic BiFeO3, giving rise to a much improved square ferroelectric hysteresis loop. A much enlarged remnant polarization (2Pr) of 144uC/cm2 and a coercive field (Ec) 386kV/cm are demonstrated with the bilayered structure, which also shows a large nonvolatile polarization (DP=Psw-Pnsw) of 122uC/cm2 at 20us. Further interestingly, it exhibits little polarization fatigue up to 5x10(power 10) switching cycles, together with a well established ferromagnetic loop with saturation magnetization of 0.62 emu/cm3 and coercivity of 200 Oe. In the bilayered multiferroic structure consisting of BiFeO3/CoFe2O4, growth of the CoFe2O4 phase was enhanced by the top BiFeO3 layer. It exhibits the desired both ferroelectric and magnetic behavior at room temperature, where the remanent polarization (2Pr) is measured to be ~146 ?C/cm2 and coercive field (2Ec) is ~1803 kV/cm, together with a saturation magnetization (2Ms) of 140 emu/cm3 and coercive field (2Hc) of ~2.7 kOe. The leakage current behavior of the bilayered multiferroic structure is shown to be consistent with that of the space charge limited conduction. 11:45 AM *R2-S2.4 (invited) Gigantic magnetoelectric and magnetocapacitance effects have been found in single crystal TbMnO3 which can be attributed to switching of the electric polarization induced by magnetic fields. Moreover, the spontaneous electric polarization P parallel to the c axis appears below lock in temperature. The crystallographic behaviors of (Tb1-xNax)MnO3-y (0 <= x <= 0.3) have been studied by a combination of neutron powder diffraction (NPD), synchrotron X-ray powder diffraction and Raman spectroscopy. Although Na+ ions have larger ionic radii than Tb3+ ions, analysis of NPD data reveals that the decrease in cell volume upon Na-doping can be explained by the occurrence of oxygen vacancies and is not due to the size effect. Based on the bond valence sum calculations and Mn K-edge X-ray absorption spectroscopy (XAS) analyses, the Mn ions in (Tb1-xNax)MnO3-y almost entirely remain in the trivalent high-spin state. These results indicated that Na-doping in (Tb1-xNax)MnO3-y leads to producing oxygen vacancies and counterbalances the increase of the Mn valence. 12:00 PM R2-S2.5 Stoichiometric lithium niobate (SLN) is preferred for many applications as it contains less intrinsic defects like Li-site vacancies and Nb anti-sites which are predominant in congruent lithium niobate (CLN). Also, many of its properties like laser induced damage resistance and diffraction sensitivity for holographic recording are enhanced at relatively lower threshold concentrations of suitable dopants. SLN crystals can be grown using Li rich [1] and K added [2] melts. In this investigation SLN single crystals of 20mm diameter and 20mm length were pulled along c-axis from 58mol% lithium rich, using conventional Czochralski puller. Each growth run was initiated typically with 200gm of charge. The amount of melt crystallized was limited to 10% to avoid compositional variation along the length of the crystal. ZnO doping enhances the damage resistance of lithium niobate above a threshold level of 2.5mol%. Co-doping of Nd is intended for using the crystal as laser host material. Hence Nd:Zn co-doping was carried during growth. The MIR spectra of 2.5mol% ZnO: SLN crystals co-doped with various Nd concentrations show a shift in OH absorption peak from 2.88&mum (pure SLN) to 2.83&mum, which is an indication of improved damage threshold [3]. In order to reveal the domain structure well-polished c-wafers of 1.5mm thickness were etched using the mixture of HF and HNO3 in the ratio of 1:2 at 100°C for 25minutes. On the c-plates of the crystals concentric rings of positive and negative domains were observed indicating as-grown crystals are multi-domain in nature. Ferroelectric domain switching studies are carried out at high temperature in the range of 800-950°C. The c-cut samples used for switching experiments were annealed at 1000°C after applying the conducting platinum paste on +c and -c faces. Doping seems to have a positive effect on domain switching rates. Nd doped crystals switch faster than the pure crystals. Expectedly, switching time decreases (by three orders of magnitude) at high temperature (950°C) for these crystals. The details of the damage studies along with the experiments on domain switching at high temperatures will be presented in this paper.
References:
[1] K Kitamura et al. Journal of crystal growth, 116 (1992) 327-332.
[2] K Polgar et al. Optical Materials, 19 (2002) 7-11.
[3] Hongtao Li et. al. Journal of Physics and Chemistry of Solids 66 (2005) 990-993.
LUNCH 12:30 PM - 2:00 PM 2:00 PM *R2-S3.1 (invited) The key issue for realizing the spintronic technology is to manipulate at will both the spin and charge degrees of freedom of electrons. Half metals (HMs) are unique materials, which are metallic for electrons of a single spin channel, and are expected as the fundamental block in spintronics. All HMs confirmed so far show net magnetism. These so-called half metallic ferromagnets (HMFMs) are understood naturally from the asymmetric densities of states in the two spin channels. In principle it is possible to have the spins of the occupied states compensate completely. Dubbed as half metallic antiferromagnet (HMAFM), this material will not influence surrounding devices in applications by the stray field, which is inevitable for known HMFMs.
We have investigated theoretically a class of perovskite cuprates in order to search new HM [1,2]. The parent material Sr8CaRe3Cu4O24 is a Mott insulator due to the strong correlations of electrons; it exhibits a ferrimagnetic ground state with Tc=440K accompanied by charge and orbital orders in Cu cations [1]. Based on first-principles calculations within the DFT+U scheme, we found [2] that doping one hole, which can be realized by replacing one of the eight divalent Sr atoms with one univalent Rb or K atom (known as A-site substitution), makes the system metallic in a single spin channel, and thus HM; the net magnetization of the parent ferrimagnetic compound is cancelled by the spin of the doped hole, and thus the system shows no macroscopic magnetization. This new compound is thus predicted to be a candidate of HMAFM.
This work is a collaboration with Y.-M. Nie.
References:
[1] X.-G. Wan, M. Kohno, and X. Hu, Phys. Rev. Lett. vol. 94, 087205 (2005); vol. 95, 146602 (2005)
[2] Y.-M. Nie and X. Hu, Phys. Rev. Lett., in press 2:15 PM *R2-S3.2 (invited) Polystyrene coated Fe3O4 nanoparticles exhibit intergranular tunneling magnetoresistance (MR) ratio of 22.8% at room temperature and a maximum MR of 40.9% at 110 K. The drastic enhancement of the MR ratio clearly suggests that there is high degree of spin polarization even at room temperature for half metallic Fe3O4. The derived spin polarization P is about 54% and 83% at room temperature and 110 K, respectively. The improvement was achieved by controlling the surface of Fe3O4 through surface engineering using oxygen-free insulating barriers. Knowing that the results provided only a lower limit on the spin polarization of Fe3O4, it has the potential to play an important role in spintronic devices.
In a related investigation, films of Fe3O4 were prepared with laser molecular beam epitaxy deposition on a Si substrate with a native SiO2 layer. When the temperature is increased above 250 K the resistance drops rapidly because the conduction path starts to switch from the Fe3O4 film to the inversion layer underneath the SiO2 via thermally assisted tunneling. A greatly magnified low field negative magnetoresistance of Fe3O4 is observed at 280 K. The effect is similar to a metal-oxide-semiconductor-field-effect-transistor (MOSFET). Reminiscent of a MOSFET, the negative MR of Fe3O4 reduces the gate voltage and causes an increase of current in the inversion layer. Thus the measured resistance is much reduced and a greatly amplified low-field negative MR is achieved at 280 K. The amplification of magnetoresistance in this Fe3O4-SiO2-Si MOSFET structure is different from the spin-transistors currently pursued in many laboratories but reveals a new route to achieve integration of spins and electronics and may have useful applications. 2:30 PM R2-S3.3 Spintronics (or spin electronics) is a very promising approach for achieving further miniaturization, higher speed and lower power consumption of consumer electronic devices like laptop computers and MP3 players. Spintronic devices specifically exploit the spin properties of the electrons (i.e. its magnetism) instead of, or in addition to, the charge degrees of freedom. [1,2]. The prototype device that is already in use in industry as a read head in hard disk drives and as a memory-storage cell, is the giant-magnetoresistive (GMR) sandwich structure (the 2007 Nobel price was awarded to Peter Gruenberg and Albert Fert for this discovery).
Polarized neutron reflectometry (PNR), soon available at the new OPAL research reactor at ANSTO, is an ideal tool for investigating vector magnetization profiles in thin film systems for future spintronic applications. The method has been used successfully for many years, for example, to demonstrate oscillatory exchange coupling in magnetic multilayers which was essential for the understanding of the GMR effect. Similarly essential for the functioning of the GMR sensor is the exchange bias effect. In my lecture I will present recent PNR results on chemical order-induced exchange bias in FePt3 epitaxial thin films, a material which has the remarkable property that, depending on the degree of chemical order, a ferromagnetic (FM) and an antiferromagnetic (AFM) magnetic state can coexist at the same temperature [3].
[1] S. Parkin, X. Jiang, C. Kaiser, A. Panchula, K. Roche, M. Samant,
Proceedings of the IEEE 91(5), 661 (2003).
[2] C. Chappert, A. Fert, F.N. Van Dau, Nature Materials 6, 813 (2007).
[3] D. Lott, F. Klose, H. Ambaye, G.J. Mankey, P. Mani, M. Wolff , A. Schreyer, H. M. Christen, and
B.C. Sales (submitted to Phys. Rev. Lett., Dec. 2007) 2:45 PM R2-S3.4 The magnetoelectric (ME) effect is defined as the appearance of magnetization induced by applied electric field and vice versa. A Cr2O3 is a representative magnetoelectric material and/or an antiferromagnetic insulator with the Neel temperature of 308K. The purpose of this work is to investigate epitaxial growth conditions of the ME Cr2O3 thin films which are expected to be applied to novel functional oxide electronic devices.
The films were prepared by an off-axis DC-RF hybrid magnetron sputtering method with following sputtering conditions; typically substrate temperature was 773-913K, RF power 100 W, DC current 0.04 A, total gas during gas pressure 0.26 Pa, Ar/O2 flow ratio 8/2 ccm, and sputtering time 240 min. The studied substrates were Al2O3(1-102) (r-cut sapphire), Al2O3(11-20) (a-cut sapphire) and Al2O3(0001) (c-cut sapphire). These sapphire substrates were annealed at 1273K for 12hour in air after chemical treatments using dilute HF solution and acetone washing.
Surface morphology of the obtained films was observed by AFM (Atomic Force Microscopy). The crystal structure was analyzed by XRD (X-ray diffraction) with θ-2θ scan method, and in-plane crystal structure of the film surfaces was investigated by RHEED (Reflection High Energy Electron Diffraction).
As the results the epitaxial growth was confirmed in the crystalline relationship: Cr2O3(1-102)//Al2O3(1-102), Cr2O3(11-20)//Al2O3(11-20) and Cr2O3(0001)//Al2O3(0001). The optimized substrate temperature to obtained superior crystallization was ca. 853K in the case of Cr2O3(1-102)//Al2O3(1-102) and Cr2O3(11-20)//Al2O3(11-20). A surface roughness average (Ra) of the (1-102) and (11-20) thin film was 1.31nm and 1.13nm, respectively. Then a full width half maximum (FWHM) of a rocking curve for Cr2O3(1-102) and Cr2O3(11-20) Bragg reflection was 0.53 degree and 0.33 degree, respectively. On the other hand, the good epitaxial growth was observed on 873K substrate in Cr2O3(0001)//Al2O3(0001). The Ra value of the thin film was 0.28 nm, and FWHM of a rocking curve for Cr2O3(0006) Bragg reflection was 0.23 degree.
The obtained results were discussed from a film growth mechanism point of view. Conclusively, it was shown that a good single crystal ME Cr2O3 thin film was obtained at 873K on c-cut sapphire substrates. The ME film is promising for multiferroic oxide device applications. 3:00 PM R2-S3.5 Complex cobalt oxide perovskites with general formula RBaCo2O5+x (R=rare earth) have been attracted considerable interests because of their interesting properties: magnetic and metal-insulator transitions, giant magnetoresistance, ionic conductivity and a structural similarity to high temperature superconductors. All the compounds are oxygen non-stoichiometric (0 AFTERNOON BREAK 3:30 PM - 4:00 PM 4:00 PM R2-S4.1 Mn distribution in GeMn thin films grown on Ge and Si substrates
Y. Wang and J. Zou
University of Queensland, St. Lucia, OLD 4072, Australia
Z. M. Zhao, X. H. Han, X. Y. Zhou and Kang L. Wang
University of California at Los Angeles, California 90095, USA
Diluted magnetic semiconductor (DMS), aiming to make use of both the charge and the spin of electrons, has been investigated extensively due to their promising applications in spintronics [1]. In particular, GexMn1-x DMS, which is compatible with current Si microelectronics, has attracted considerable attention. However, the fact that the low solubility of Mn in Ge makes it a challenge task to obtain a room-temperature ferromagnetic GexMn1-x DMS with high concentration and uniformly distributed Mn. On the other hand, the issue that whether Mn is incorporated into Ge lattice or is segregated to form GeMn clusters is of critical importance since the distribution of Mn atoms can critically affect their charge state and magnetic coupling. Therefore, the knowledge from the nature of Mn distribution is essential to understand the origin of ferromagnetism of GexMn1-x DMS films.
In this study, Ge0.96Mn0.04 thin films with different film thickness were grown on both Ge (100) and Si (100) substrates using molecular beam epitaxy and subsequently annealed. The Mn behavior in the GeMn thin films grown on Ge (100) and Si (100) substrates were investigated using advanced transmission electron microscopy. It has been found, for the GeMn thin films grown Si, (1) Mn tends to diffuse toward to the surface and (2) when the Mn concentration is sufficiently high, Mn5Ge3 clusters can be formed near the surface [2]. However, for the case of GeMn thin films grown on Ge, Mn is diffused randomly [3]. The facts that (1) there is a lattice mismatch between Ge and Si and (2) that Mn atomic radius is larger than that of Ge suggest that the tendency of Mn moving towards surface during the thin film growth on Si can be attributed to the requirement of the strain relaxation.
[1] H. Ohno, Science 281 (1998) 951.
[2] Y. Wang, J. Zou, Z. M. Zhao, X. H. Han, X. Y. Zhou and Kang L. Wang, J. Appl. Phys. (2008) DOI: 10.1063/1.2875110
[3] Y. Wang, J. Zou, Z. M. Zhao, X. H. Han, X. Y. Zhou and Kang L. Wang, Appl. Phys. Lett. (2008) DOI:10.1063/1.2884527
We acknowledge the financial support from Australian Research Council. 4:15 PM R2-S4.2 Abstract:
The discovery of particular electronic structure in graphene layers has opened a way to their applications in microelectronics. However, the growth manner of graphene layers on substrate is not clear. Moreover, a relationship between the layer number n and the critical radius Rc of the graphene cylinder has not been defined quantitatively. Recent advances in the research of graphene show that the sheet could grow horizontally when R < Rc whereas it grows through the nucleation around the cycle of the sheet or through the formation a new layer atop when R > Rc. In this work, a thermodynamic model was established to describe the Rc(n) function of graphene layers deposited on SiO2 substrate in consideration of surface free energy Gs contributions to the total free energy G. It was found that Rc increases linearly as n increases and the accuracy of the developed model was verified with the reported experimental data. 4:30 PM R2-S4.3 We have successfully fabricated highly (up to 7%) Mn-doped Ge thin films on Si substrates by laser ablation technique. The deposited samples were annealed at 600oC for 30 mins at a vacuum of 5x10E-6 mbar. X- ray diffraction analysis shows no peak other than Ge (220). The lattice constant of the grown layer calculated from Ge (220) peak shows a higher value than that of bulk Ge due to the larger Mn atomic radius compared to Ge, strongly indicating that Mn ions are being incorporated into the host Ge lattice. X-ray reflectivity analysis has been carried out for the determination of film thickness and interfacial roughness. Fitting the X-ray reflectivity profiles using the Parrat 32 software, we obtained EDP after normalization with the packing fraction. The EDP shows that the composition for the sample is Mn0.07Ge0.93. The current-voltage (I-V) characteristics of Al/ MnxGe(1-x)/Si Schottky diodes have been measured over the temperature range of 70-280 K. The analysis based on the thermionic emission (TE) theory has revealed an abnormal decrease of zero-bias barrier height and the increase of ideality factor at lower temperatures. This behavior has been interpreted on the basis of the assumption of barrier height inhomogeneities that prevail at the interface. Temperature dependent resistivity measurement of the samples in the presence of magnetic field shows typical metallic behavior. For T<150K, the in-field resistivity shows less value that the zero field resistivity. But for T>150K, the in-field resistivity shows a higher value than the zero field resistivity. Alloys with Mn impurity showed magneto impedance (MI) effect due to the presence of magnetic ions. Magneto-impedance analysis has been carried out using a magnetic field of 100 Gauss. We can distinguish two main frequency ranges of GMI. At low frequency (f< 1MHz), a single peak behavior is observed but for higher frequency a two peak behavior can be observed. We have also investigated the frequency response of the samples at four different DC magnetic fields. The real impedance has a plateau at frequencies < 10 kHz, followed by a fall with the increase in frequency. At the frequency where the real part of impedance deceases, the imaginary impedance shows a maximum. With increasing frequency there exist another drop in the real part of the impedance and hence a corresponding maxima in the imaginary part of the impedance. We have explained these results by two dominant magnetization processes: domain wall bulging for low frequency and magnetization/spin rotation for high frequency. 4:45 PM R2-S4.4 Zinc oxide based diluted magnetic semiconductors have attracted great interests due to the theoretical prediction that above room temperature ferromagnetism can be achieved by doping wide bandgap material, ZnO, with transition metal (TM) [1]. Although, experimental results revealed ferromagnetism above room temperature, small magnetic moments were observed for 3d-TM doped ZnO. This is attributed to intrinsic n-type carriers in ZnO compensating the hole carriers that mediate ferromagnetism in 3d-TM doped ZnO. On the other hand, experiment results on 4f rare-earth (RE) doped GaN produced large magnetic moment and ferromagnetism above room temperature [2]. This raised interest in RE doped ZnO. Recent reports on Gd doped ZnO up to 1.5 % atomic concentration had revealed room temperature ferromagnetism with saturation moment up to 1.8 µB/Gd [3].
We present structural and magnetic properties of ZnO films doped with Gd magnetic ions at various concentrations, achieved by ion implantation technique and pulsed laser deposition (PLD) on ZnO (0001) single crystals and sapphire. The Gd+ ions were implanted at energy of 180 keV using four different dosages varying from 1.5 x 1015 cm-2 to 1.5 x 1016 cm-2. The implanted samples were further annealed at 550 °C for 15 mins in high vacuum furnace (<10-4 Pa). Thin films were grown on sapphire substrate at temperature of 650 °C and oxygen partial pressure of 7.5 x 10-5 Torr. The films chemical compositions were varied using four targets of different Gd concentrations, to give nominal concentration, x varying from 1 % to 7 %. X-ray diffraction (XRD) showed a shift of ZnO peak indicating a large strain is induced in the as-implanted and the PLD grown films. The magnetic properties of the films were measured using the superconducting quantum interference device (SQUID) magnetometer. Magnetization as a function of temperature revealed a positive magnetization at 305 K and a concave trend was observed for all samples for both implanted (annealed) and PLD grown samples. The M-H loop was carried out at 5 K and 300 K. The coercivity was observed to be generally higher for implanted films (annealed) than PLD grown samples. This can be attributed to the high defect density in the implanted films. The highest saturation magnetization was achieved for the dosage of 9.0 x 1015 cm-2 and x = 5 % for the implanted (samples) and PLD grown films, respectively. This suggested that the Gd ions solubility limit is reached in these samples.
Reference
[1] T. Dietl, H, Ohno, F. Matsukura, J. Cibert, D. Ferrand, Science 287, 1019 (2000).
[2] S. Dhar, O. Brandt, M. Ramsteiner, V.F. Sapega, K.H. Ploog, Phys. Rev. Lett. 94, 037205 (2005).
[3] K. Potzger, Shengqiang Zhou, F. Eichhorn, M. Helm, W. Skorupa, A. Mücklich, J. Fassbender, T. Herrmannsdörfer, A. Bianchi, J. Appl. Phys. 99, 063906 (2006). 5:00 PM R2-S4.5 The theoretical description of strongly correlated electrons remains a challenge in condensed matter physics, and the rare earths and their compounds are a particularly fertile testing ground for new treatments. Their highly localized 4f atomic orbitals result in large magnetic moments that couple strongly to the extended-state electrons in the valence and conduction bands. One of their simplest bonding configurations, the rock-salt structure of the rare earth mononitrides, is particularly amenable to treatment, and recent computed band structures have been used to predict their transport and magnetic behaviour. However, there are remarkably few measurements of the quality required to test the often disagreeing predictions.
In this paper we report the growth of GdN thin films, including epitaxial films, by vacuum evaporation and pulsed laser deposition. Furthermore we have developed capping procedures that prevent the reaction in air that has been a major contributor to earlier uncertainties about such basic questions as whether they are metals or semiconductors. We have studied the films in situ and ex situ (on capped films) to determine their crystal texture, conductivity and magnetic order. We find that GdN is a very soft ferromagnetic semiconductor with a Curie temperature of 70 K and a moment of 7 ?B per Gd ion. Optical transmission spectroscopy shows a band gap of 1.3 eV at ambient temperature and 0.9 eV in the low-temperature ferromagnetic phase, results that have guided a refined choice of parameters in a LDA+U band structure calculation. X-ray absorption and emission spectroscopies yield conduction- and valence-band densities-of-states in close agreement with the calculation. These data will be compared with preliminary results of band structure measurements on a number of other rare-earth nitrides. 5:15 PM R2-S4.6 The magnetic and magnetoimpedant behaviours of FeCuCrVSiB films and (F/SiO2)3/Ag/(SiO2/F)3 (F=FeCuCrVSiB) multilayer films deposited in a magnetic field have been investigated systematically. The samples were deposited by the rf sputtering with or without a dc magnetic field of 900 Oe applied in the film plane. It is found that the magnetic field applied during the deposition process improves the soft magnetic properties of the sample significantly. The coercive force of the sample is about 0.8 Oe, which is much smaller than that deposited without a field. Moreover, remarkable GMI effects were obtained at relatively low frequencies, which contrasts with the samples deposited without field. In the field-deposited state, the maximum GMI ratios of 21.5% and 19.5% were achieved for the single-layer films in longitudinal and transverse fields at a frequency of 13MHz, while for the multilayer films, the maximum values of longitudinal and transverse GMI ratios are45% and 44% at a frequency of 6.81 MHz, respectively. These superior GMI behaviours of the as-deposited films are related to the magnetic field used in the preparation process and the inserted SiO2 layers. R2-S5.1 We present and discuss high spectral and spatial resolution Raman spectra taken at the room temperature, in the depth of YBCO films with different thickness, critical temperature and crystal orientation. We utilize the 488 nm excitation wavelength of the visible light that has the resonance effect for the most significant Raman peaks on YBCO films.
Beside the crystalline structure quality, revealed by the 100 cm-1- 800 cm-1 Raman spectrum range, we discuss the electronic Raman continuum from 100 cm-1-2100 cm-1 spectrum range, correlating with superconducting properties of YBCO films.
Typical scanning electron microscopy pictures of thin and thick in-situ grown YBCO films are presented. The interrelations between surface morphology showed by these pictures and the epitaxial growth of the crystalline structure, revealed by depth Raman profiling spectra have been investigates. R2-S5.2 Boron powder with a low purity of 95-97% was planetary ball-milled with different milling times from 1 to 10 h at a speed of 200 rpm using toluene as a medium. With increasing milling time, the particle size decreased and the semi-crystalline phase of the boron powder became an amorphous phase. The mechanically ball-milled boron powders were then treated with glycerin as a carbon source. The MgB2 pellets were made from various conditions of boron powders, and then heat-treated at a temperature of 900 degrees C for 30 min. As the milling time increased from 1 to 5 h, the critical current density (Jc) increased over the entire magnetic fields. However, the Jc value decreased due to a deterioration of the crystallinity in the case of a 10 h milling as revealed by the drastic decrease of the critical temperature. The glycerin-doped MgB2 with boron powder mechanically milled for 2 h showed a Jc enhancement of almost 100 times at 8 T when compared to MgB2 with raw boron powder without any treatment.
This research was supported by a grant (R-2006-1-248) from Electric Power Industry Technology Evaluation & Planning, Republic of Korea. R2-S5.3 In our study, we studied the phase transformation of in situ processed MgB2/Fe wire used boron powders of 96 and 99% grade. Fabricated wire samples were estimated by using DTA (Differential thermal analysis) measurements. It was observed that formation temperatures of the MgB2 phase for samples used 96% boron were slightly shifted to higher temperature. This is due to degradation of reaction between powders, indicating that reaction temperature is very sensitive to crystalline phase of the boron powder. This reaction mechanism is considered to be moderated by magnesium vapor diffusion across grain boundaries of the boron powder. R2-S5.4 The superconductivity of nano SiC doped MgB2 sintered in pulsed magnetic field (PMF) was investigated with Raman scattering measurements and Raman spectral fit analysis. The superconductivity for the sample sintered in 5T PMF is improved compared with that of the sample sintered without PMF. The improved critical transition temperature, Tc, is attributed to the strengthening of the electron-phonon coupling (EPC) in MgB2, as reflected by the broadened E2g mode in the Raman spectra. Both the frequency and linewidth of the E2g mode are increased after the PMF processing. The crystals of nano SiC doped MgB2 sintered in PMF show more harmonic features in the Raman response so as to allow for improved Tc. Magnetic field processing technology has been proved to be a powerful tool to improve the superconducting properties of SiC doped MgB2 superconductor. R2-S5.5 RuSr2RE1.5Ce0.5Cu2O10(Ru-1222) and RuSr2RECu2O8 (Ru-1212), where RE= Gd, Eu, Sm are the systems which shows the coexistence of high temperature superconductivity and ferromagnetism. We explore here in detail the nonlinear susceptibility (NLS) behavior of RuSr2Eu1.5Ce0.5Cu2O10. NLS is a vital tool to probe the various magnetic phases in the material because most of the subtle features undetectable by linear susceptibility can be observed in NLS. The presences of non-zero second harmonic ac susceptibility, shows the presences of ferromagnetic (FM) component in Ru-1222 samples. The third harmonic susceptibility (χ3) shows typical features of spin glass (SG) in Ru-1222 system: In low field limit, χ3 shows diverges of the form χ3 ∝ ε −γ, where ε = (T−Tg) ⁄Tg and Tg is the peak temperatures of temperature dependent ac susceptibility and γ is susceptibility exponent. Secondly, with the applied field and frequency → zero, χ3 shows divergence. Also, the sharp negative peak in χ3 indicates SG state. However, the fitting of temperature variation of first and third harmonic ac susceptibility χ1 and χ3 to Wohlfarth's model of superparamagnetism (SPM) indicated the possibility of SPM in Ru-1222 system. The presence of minority Ru-1212 and SrRuO3 phases form FM nano clusters within Ru-1222, which may give rise to SPM whereas dominant SG behavior originates from majority Ru-1222 phase, results in the coexistence of SG and SPM along with FM ordering in Ru-1222 system. R2-S5.6 The superconducting properties of the MgB2 bulk samples prepared through high energy ball milling system were characterized systematically. In this study, we did ball mill the commercial low purity 96% boron powder, which has poor reactivity due to its crystalline phases. Ball milling process was carried out with different times and speeds. We found that critical current density of the undoped MgB2 improved for 5 hours ball milled processing. In addition, further enhanced critical current density through carbon (C) doping was observed. R2-S5.7 Perspective [1] for qubits Josephson Mo-Re alloy-oxide-Pb, Mo-Re alloy-normal metal-oxide-Pb and Mo-Re alloy-normal metal-oxide- normal metal-Mo-Re alloy junctions have been fabricated and investigated. Thin (~50-100 nm) MoRe superconducting films are deposited on Al2O3 substrates by using a dc magnetron sputtering of MoRe target. Normal metal (Sn, Al) thin films are deposited on the MoRe films surfaces by thermal evaporation of metals in vacuum and oxidized to fabricate junctions oxide barriers. Quasiparticle I-V curves of the fabricated junctions were measured in wide range of voltages. To investigate a transparency spread for the fabricated junctions barriers the computer simulation of the measured quasiparticle I-V curves have been done in framework of the model of multiple Andreev reflections in double-barrier junction interfaces. It's demonstrated the investigated junctions can be described as highly asymmetric double-barrier Josephson junctions with great difference between the two barrier transparencies [2,3]. The result of the comparison of experimental quasiparticle I-V curves and calculated ones is proposed and discussed. Results of computer simulation of quasiparticles I-V curves of junctions are presented and discussed.
The IC(T) characteristics, measured for Josephson heterostructures with different thickness of metal layer s and exposure dose E, essentially deviate from an Ambegaokar- Baratoff (A&B) IC(T) behavior and Kulik-Omelianchuck (K&O) curves, because of proximity effect caused by the comparatively high value of s (up to 100 nm). We study theoretically two extreme limits: the clean and the dirty limit for the interlayer between the superconducting electrodes and discuss the thermal stability of the junctions characterizing it with the temperature derivative dIC/dT . The combined experimental and theoretical analysis of the problem provides a way for understanding, controlling and improving the design of the MoRe/Al-AlOx/MoRe junctions in order to enhance their reliability.
Also I-V curves of the fabricated junctions have been measured under microwave irradiation with 60 GHz frequency , clear Shapiro steps in the measured I-V curves were observed and discussed. R2-S5.8 Structural analysis and electromagnetic measurements have been performed on a range of samples prepared by the liquid mixing approach to doping MgB2 superconductor. The dopants used to enhance the current carrying ability of MgB2 are sugar, malic acid and polycarbosilane. The results obtained have allowed us to clarify the individual contributions of microstructural defects on the critical current limitation at low and high magnetic fields in doped MgB2 superconductors. These defects in the MgB2 microstructure include porosity and non-superconducting phase ("geometrical" defects), as well as the connectivity and transparency of grain boundaries. The results of analysis showed that i) the elimination of the "geometrical" defects would result in critical current densities that are a factor of 1.5-2 higher than currently measured values; ii) the low field Jc values are mainly determined by the connectivity and transparency of grain boundaries; iii) in field Jc(Ba) performance is affected by mentioned above defects in the microstructure to a lesser extent, and its behaviour is mainly determined by the pinning environment in the samples. It also was observed that while a denser pinning network favors in field Jc(Ba) behaviour, this results in reduction of grain boundary transparency and more pronounced critical current density limitation in the low field region. R2-S5.9 Many experiments have shown that of all the rare earth elements, only Ce, Pr and Tb are exceptive, whose doping was not with superconductivity while with the same crystal structure as other Y123 superconductors. Here, CeBa2Cu3O7-? and TbBa2Cu3O7-? isn't crystalline stable, while Y1-xPrxBa2Cu3O7-?(YPr123 systems) is easily formed in single-phase structure for all Pr content x=0.0-1.0. Therefore, to answer the question why PrBa2Cu3O7-?(Pr123) does not superconduct is possibly essential to help to determine the nature of the superconductivity. The typical general results for Pr substitution are that there are a monotonic decrease in Tc and eventually a metal-insulator transition with increasing Pr concentration and that there are also ion size effect which shows that in R1-xPrxBa2Cu3O7-?(R=Rare Earth ), Pr suppressed superconductivity more seriously as the rare earth's radius increase. Theoretically, some models, such as magnetic pair breaking, hole filling, carrier localization, and so on, have been proposed to explain the phenomena above. Magnetic and pinning force behavior is a kind of important characteristics in both conventional superconductor and layered cuprate superconductor. Studies of flux behavior in superconductor are of interest from the viewpoints of both fundamental research and practical application. In order to explain the anomalous behavior of Pr123, in the present work, the magnetization and flux pinning results at various temperatures are reported for Y0.93Pr0.07Ba2Cu3O7-? (YPBCO) single crystals. The samples were prepared by top-seeded solution growth method. The magnetic field dependence of critical current density , pinning force density and the phase diagram are also given for YPBCO single crystals. The results show that the value of the ratio of the maximum pinning force field irreversibility field is at around 0.33. Flux pinning mechanisms is also discussed in different magnetic field by the scaling function as well as the ratio of the pinning force field at and . The results are compared with doping free YBCO sample, which this probably is an explanation to Pr suppressed superconductivity. R2-S5.10 We report the carbon substitution for B in MgB2 superconductor. The lattice parameters, resistivity (R), upper critical field (Hc2), and irreversibility field (Hirr) as a function of different sintering temperatures were studied. Optimized sintering parameters were set up in term of the superconducting properties. The using of sucrose (C12H22O11) as the C source resulted in a depression in Tc, but significantly increased the critical current density in field. C substitution for B induced defects and lattice strain, and as a consequence, improved the Hc2 and Hirr. SEM images show different microstructures of un-doped and sucrose-doped samples, the smaller grain size caused by the doping may contribute to the Jc increase in the higher field due to grain boundary pinning. R2-S5.12 Novel Fabrication of Hollow Polystyrene/Magnetite Microspheres and Their Magnetorheological Characterization
Ji Hye Kim , Fei Fei Fang , Hyoung Jin Choi*
*Department of Polymer Science and Engineering, Inha University, Incheon 402-751, Korea; hjchoi@inha.ac.kr
Magnetorheological (MR) fluids named as fantastic or intelligent fluids are capable of being solidified with an aid of an external magnetic field and re-liquefied by removing the magnetic field. This abrupt state-changing process which causes obvious rheological properties has great potential in designing diverse high performance engineering products including damper active systems, torque transducer and MR polishing equipment. Generally, high yield stress, low apparent viscosity without magnetic field as well as good stability and durability have become very crucial factors to widen the application of MR fluids. Those magnetic materials that have high saturation magnetization have been considered as superior candidates for MR fluids. However, serious sedimentation of the MR fluid due to large density mismatch between magnetic particles and medium oil limits its applicability. Therefore, many strategies have been explored to solve this problem. In this study, we fabricated novel hollow polystyrene/magnetite microspheres by adopting porous polystyrene as core material and magnetite as shell material. The porous morphology of polystyrene was obtained by etching silica particles which were coated on the surface of polystyrene. After depositing magnetite on the surface of porous polystyrene, the product was dispersed in oil to prepare MR fluid. SEM images, FT-IR spectra, TGA data and XRD pattern help to confirm the intermediate pores of polystyrene and the finally covered magnetite. At last, the magnetic property (VSM data) as well as the MR performances were investigated at 20?C via a rotational rheometer (Physica MCR 300, Stuttgart, Germany) equipped with a MR device (MRD 180) with its typical MR characteristics. R2-S5.13 Multiferroics of the perovskite type RMnO3 (R = Dy, Gd, Tb) have at-
tracted considerable attention in recent times. In this respect, DyMnO3 is of
specific interest since its ferroelectric transition and corresponding flop of po-
larization from c to a axis can be triggered by the application of a magnetic
field. Also, substitution of cations with different ionic radii at the A-site
distorts the structure, introduces disorder, and enhances antiferromagnetic
superexchange interactions over ferromagnetic interactions. It is known that
size mismatch and A-site cationic disorder are detrimental to the colossal
magnetoresistive properties of ferromagnetic manganites near ideal doping
and is a crucial factor for generating a spin-glass insulating state. Here we
report the magnetic properties of Dy0.50 Sr0.50 MnO3 single crystals grown us-
ing float-zone method under gaseous atmospheres of argon, nitrogen and air.
Dy0.50 Sr0.50 MnO3 crystallizes in a cubic structure Pm3m, irrespective of the
atmosphere used during growth. This is unlike the trend observed in the
parent RMnO3 where a change in the growth ambience from argon/nitrogen
to air changes the crystal structure from hexagonal to orthorhombic. We
observe that the temperature dependence of inverse magnetic susceptibility
of Dy0.50 Sr0.50 MnO3 follows a Curie-Weiss law down to 40 K. Magnetisation
measurements under field cooled and zero-field cooled conditions display irre-
versibility below 35 K. Frequency dependence of the peak in ac susceptibility
data follows a critical slowing down with exponent z? = 3.6. Specific heat
measurements reveal a sizable linear contribution at low temperature that
may be associated with the glassy magnetic ordering and a Schottky-like
anomaly in a wide temperature range between 8 and 40 K. It is argued that
the spin-glass state originates from the A-site disorder which in turn results
from the random distribution of cations with different ionic radii. Details of
these measurements and results will be presented in this paper. R2-S5.14 To invent modern magnetic materials making devices with large magnetoresistance function at room temperature is highly yearned to the contemporary spintronics. Correspondingly, the innovation and creation of room-temperature half-metallic materials is boosting rapidly.
We formulate a scheme to find candidates of room-temperature half-metallic materials among plenty synthesized cuprates with high T_{c}, by means of doping carrier(s), which can be experimentally achieved by the typical operation of A- or B-site cation-replacement. The working rationale is taking advantage of Hubbard repulsion of d-electrons of Cu-atoms and the charge-transfer effect from the associated O-ligand to fully polarize the spin of doped carrier. Such a scheme has been validated in the invented half-metallic systems as the doping modifications of the state-of-art octuple-perovskite Sr$_{8}$CaRe$_{3}$Cu$_{4}$O$_{24}$, an insulating ferrimagnet with T_{c} around 440K, relying on First-principle calculations within the scheme of DFT+U [1].
Since the data base of synthesized cuprates is huge, including the flood of perovskite cuprates originally synthesized for the research of high-temperature superconductivity in the past two decades, it is expected that the present scheme can shed light on a new way to find new half-metallic materials.
Reference:
[1] Y.-M. Nie and X. Hu, Phys. Rev. Lett. in press. R2-S5.15 Cu3Mn is a substitutionally disordered face-centred-cubic alloy and a model spin-glass system with a relatively high paramagnetic to spin-glass transition temperature of 110K. A spin-glass system exhibits a high degree of magnetic frustration with no true ground state condition. Tight binding analysis suggests that for the case of the CuMn system the Mn d-band is mainly located at the Fermi level leading to a potential electronic instability at the transition temperature [1] Angle resolved valence band photoemission directly probes the detailed valence band electronic structure E(n,k). The bulk band structure of Cu3Mn{100} along the Γ-Δ-X direction was determined using normal emission spectra acquired at photon energies from 15-160 eV and assuming free-electron final state bands. Transitions were identified and critical point energies determined by structure plot analysis. Off-normal spectra along the two major symmetry directions, and were acquired at a number of photon energies in order to derive the surface state/resonance band structure. Experimentally derived band structures are compared with calculation from the literature and to a calculation assuming a stoichiometrically ordered fcc-alloy with a Cu3Au structure. Interestingly no d-bands are observed to pass through the Fermi level along normal emission, Γ-Δ-X, while d-band dispersion through the Fermi level is clearly observed in the off-normal data sets. We analyse whether these bands may be involved in the spin-glass transition.
Travel Support by the Australian Synchrotron Research Program is gratefully acknowledged.
[1] J. Hafner, R. Lorenz, Comput. Mat. Sci. 8 (1997) 170-181. R2-S5.16 The multiferroic behavior, observed in manganites containing small rare-earth cations, has attracted considerable attention in recent times because of the interesting physics involved as well as their high application potential (1). Colossal Magnetoresistance exhibited by mixed valence perovskites has motivated us to study the effect of strontium substitution in multiferroic gadolinium manganite crystals. Single crystals of these multiferroic oxides were grown by Float Zone (FZ) technique. Initially, Gd1-xSrxMnO3 compounds with different Sr-doping concentration (x= 0.5, 0.6) were synthesized by solid state reaction. Crystals were grown using four mirror optical image furnace with a typical growth rate of 1 mm/hr. Crystallinity was ascertained by X-ray diffraction. Crystal composition was estimated by ICPAES analysis. Transport properties of grown crystals were studied in the temperature range 40 to 300 K. Temperature evolution of electrical resistivity of all the crystals showed semiconducting behaviour as expected (2). Magnetoresistance measurements were performed by applying magnetic field perpendicular to the direction of current. Drastic reduction in resistivity was observed for doped crystals in the presence of magnetic field. Gd0.5Sr0.5MnO3 crystals showed ~1.9E10 % MR at 45 K. At relatively high magnetic field a metal-insulator transition was also observed and this transition temperature was field dependent. The temperature and field dependence of magnetoresistance was also studied in detail. Magnetization of the samples was measured by SQUID magnetometer in the temperature range 5 to 300 K. Gd0.5Sr0.5MnO3 crystals exhibited a bifurcation in the zero-field cooled (ZFC) and field cooled (FC) plots. Electrical and magnetic properties of these crystals will be discussed in detail.
References:
(1) Kadomtseva A. M. et. al. JETP Letters, Vol. 82, No. 9, pp. 590-593 (2005)
(2) Garcia-Landa B. et. al. Journal of Applied Physics, Vol. 83, No.12,7664 (1998) R2-S5.17 Two Mn diffusion modes in magnetic tunnel junctions
Y. Wang
The University of Queensland, St. Lucia, OLD 4072, Australia
Z. M. Zeng and X. F. Han
Institute of Physics, Chinese Academy of Sciences, Beijing 100080, China
X. G. Zhang
Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA
Z. Zhang
Beijing University of Technology, Beijing 100022, China
Nowadays, magnetic tunnel junctions (MTJs) are studied extensively both by theory and experiment due to their promising potential applications in spintronics devices [e.g. 1-3]. Thermal stability, as an important issue, has also attracted great attention. It is known that Mn atoms diffuse into the barrier layer and act as magnetic impurity which can greatly reduce the tunneling magnetoresistance of MTJs. Despite a great deal of work relating Mn diffusion to annealing temperature Ta and to oxygen diffusion, and the speculation that at moderate Ta amorphous CoFeB can block Mn diffusion more effectively than polycrystalline CoFe, there is not a clear physical picture of Mn diffusion mechanism and what roles individual microstructures play.
In this study, we revealed two different mechanisms of Mn diffusion at low and high temperatures in CoFeB and CoFe-based MTJs by combining high resolution and scanning transmission electron microscopy [4]. At low temperatures it is through bulk crystalline CoFe and assisted by oxygen. It can be stopped by both amorphous CoFeB and (110)-textured CoFe. At high temperatures Mn diffuses through vacancies in bulk amorphous CoFeB and along grain boundaries of crystalline CoFe.
[1] Z. M. Zeng, X. F. Han, W. S. Zhan, Y Wang, Z. Zhang, and S. F. Zhang, Phys. Rev. B 72 (2005) 054419.
[2] Y. Wang, Z. M. Zeng, S. Rehana, X. F. Han, X. C. Sun and Z. Zhang, J. Appl. Phys. 100 (2006) 054510.
[3] Z. M. Zeng, J. F. Feng, Y. Wang, X. F. Han, W. S. Zhan, X. G. Zhang and Z. Zhang, Phys. Rev. Lett. 97 (2006) 106606.
[4] Y. Wang, Z. M. Zeng, X. F. Han, X. G. Zhang, X. C. Sun and Z. Zhang, Phys. Rev. B 75 (2007) 214424. R2-S5.18 Here, we demonstrated a one-step protocol to synthesis high-coercivity magnetic nanorods with FePt and PtTe2 mixing in a polyol process with presence of sucrose and trioctylphosphine oxide. The observed nanoparticle-nanorod-nanopartilce shape transition depending on the composition indicates the nanorods growth were achieved by combining the helical growth PtTe2 and sucrose template confinements. L10 ordering of FePt in the nanorods has been accomplished at annealing temperature as low as 400 ?C with Hc above 500mT, which is suitable for many applications such as recording, cell or bacteria manipulation and advanced magnetic composite. Formation of a uniform 10-nm silica shell is applied to protect the nanorods from coalescence during annealing. Such formation mechanism should be applicable to other metallic alloy systems and useful for the understanding of anisotropic nanocrystals growth. R2-S5.19 Complex Impedance analysis of vanadium doped SrBi2?(Ta0.9V0.1)2O9
Puja Goel , V N Ojha and K. L. Yadav*
National Physical Laboratory, Dr K S Krishnan Road, New Delhi 110 012, INDIA
+Indian Institute of Technology Roorkee, Roorkee 247667 INDIA
Email: pujagoel@gmail.com
The Polycrystalline materials have received a great attention in recent years because of the ease and low cost of synthesis. Strontium bismuth tantalate SrBi2Ta2O9 (SBT) belongs to a class of layered bismuth oxides and being considered an important candidate for ferroelectric memory based device applications. In polycrystalline materials the grain boundaries play a considerable role in the conduction process, it is worth separating the conductivity due to grain boundary from that of bulk material and the electrode polarization. Dielectric relaxation phenomenon shows a significant effect on the electrical properties of the capacitors, since the leakage current behaviour under electric fields used in actual device operation is attributed to it. During the high temperature solid state synthesis of materials many defects may create which affects the electrical response of the material significantly. Air annealing is the process which is expected to reduce the defect concentration in the above material and also to change the resistivity and capacitance notably. Therefore it has become necessary to understand the behavior of material in wide range of frequency at different temperature as the defect dipole responds as diverse frequencies. Thus, knowledge of the intrinsic relaxation is very important for the development of devices in microelectronics. Impedance and modulus spectroscopy is a popular analytical tool in materials research development because it involves a relatively simpler electrical characterization and whose results can be directly linked with the complex microstructure of the materials. In this paper we discuss the fabrication of the material and also report the complex impedance analysis. The impedance of postsinter-annealed samples for different durations (7.5 h and 24 h) in polycrystalline SrBi2?(Ta0.9V0.1)2O9 has been measured as a function of frequency using HIOKI-3532 impedance analyzer. The experimental data were measured in the temperature range of 100 0C-500 0C range and have been analyzed in the complex plane formalism and suitable equivalent circuits have been proposed in different regions. This clearly indicated the role of oxygen vacancies and the effect of annealing of the electrical properties of the materials. Imaginary part of impedance have shown a monotonous decrease with frequency upto certain temperature and then relaxation peaks start appearing into the material as the temperature increases. Presence of defects/ vacancies lead to a temperature dependent electrical relaxation process occurring in the material at higher temperatures and thereby presents a reason for the significant peak broadening in the loss spectrum. Absence of peak in loss spectrum is an indication of negligible current dissipation in the samples. The detail analysis of our calculation and work will also be presented in the paper. R2-S5.20 Multilayered thin films differing either in their structure or composition or in both have been shown to demonstrate novel magnetic, superconducting, ferroelectric or electromechanical responses. In the case of ferroelectrics, multilayers or superlattices have been demonstrated to show enhanced polarization, high dielectric permittivity and totally new structural phases. These observations have been explained on the basis of electric field induced coupling, epitaxial strain and specific polar interactions between the interfacial layers. As most ferroelectrics have a strong non-negligible ferroelastic self-strain associated with their phase transformation, an aspect that should be equally fascinating is that of the ferroelastic interactions between such multi layers. Therefore a tantalizing question is: Can we harness the ferroelastic interactions between ferroic multi layers to induce reversible motion in ferroelastics and hence enhance electromechanical properties? The ferroelastic properties of a multilayer structure comprising a zirconium rich lead zirconate titanate (PZT) film in rhombohedral phase, sandwiched between a titanium rich PZT film in tetragonal phase and a thick passive substrate are investigated theoretically. The heterostructure thermodynamic energies are examined to reveal the effects of lattice misfits on the change of the equilibrium volume fraction of ferroelastic domains. The film thickness dependence of domain formation is calculated and depicted for several cubic passive substrates. The results are then compared with the formation of ferroelestic domains of a tetragonal monolayer PZT on a thick passive substrate. It is shown that the formation of ferroelastic domains in the heterostructure is more abundant than the mono layer over a vast range of misfit strains practically observed in very thin films. The compositional variation of the PZT films is also investigated. Four PZT compositions are studied and it is shown that the higher the titanium content of the tetragonal layer, the more pronounced is the advantage of the multi layer structure. These results show new ways of the manipulation and engineering of the ferroelastic domain structure of ferroelectric thin films. R2-S5.21 A compositionally and displacively disordered Bi-based pyrochlore phase found in a range of ternary Bi2O3-M2+O-Nb2O5 systems has been the subject of much recent interest as a result of its relatively low sintering temperatures and often excellent dielectric properties including electric field tuneability. These properties make these materials attractive candidates for multilayer capacitor and integrated device applications. In our previous study, two such A2B2O(1)6O(2) pyrochlore type phases of stoichiometry Bi1.67Mg0.75Nb1.5O7 (BMN) Bi1.67Ni0.75Nb1.5O7 (BNN) were investigated and showed a clear relationship between their local crystal chemistry and good dielectric properties[1]. In this study, the effect of Ca-doping on the local crystal chemistry and dielectric properties of BMN or BNN have been investigated by means of X-ray powder diffraction, electron diffraction and dielectric temperature spectra. It was found that while Ca-doping does not obviously affect the local crystal structure it increases the dielectric constant whilst keeping the dielectric loss in the low range. The improvement in dielectric constant for Ca-doped BNN is more significant than Ca-doped BMN. A dielectric constant of 161 and dielectric loss of 0.002 was obtained for Bi1.67Ca0.19Ni0.56Nb1.5O7 at 100 kHz and at room temperature.
[1]. Nguyen HB, Noren L, Liu Y, Withers RL, Wei X, Elcombe MM The
disordered structures and low temperature dielectric relaxation properties of
two misplaced-displacive cubic pyrochlores found in the Bi2O3-MIIO-Nb2O5 (M = Mg, Ni) systems. J. Solid State Chem. (2007), 180(9), 2558-2565. R2-S5.22 Abstract: Electroless silver plating on acrylate rubber (ACM) microspheres of micron scale by replacement reaction method was studied. The morphology and composition of Ag deposits and the electrical properties of the Ag-coated elastomer microspheres were investigated. It is found that the replacement reaction method can achieve the continuously and uniformly Ag-coated conductive elastomer microspheres with low density and core-shell structure. The replacement reaction method preplates Cu on the elastomer microspheres by electroless plating and then displaces the Cu deposits by Ag. Different from the rigid particles (such as carbon black, Cu powders), the Ag-coated conductive elastomer microspheres present a special resistance behavior that the volume resistivity declines remarkably with the increase of pressure and temperature. It denotes that the Ag-coated conductive elastomer microspheres are elastic and thermal expansionary, because of the rubber matrix. The Ag-coated elastomer microspheres also have stable electric resistivity with the thermal cycle and electrifing time. This low density and high conductivity mental coated polymer elastomer microspheres can be used widely, such as the thermal/pressure sensitive elements and the conductive additive for composites, paints or adhesives.
Key words: elastomer microspheres;electroless plating;electric resistivity R2-S5.23 Rare-earth-doped oxynitride or nitride compounds have been reported to be photoluminescent and may then serve as new phosphors because of their good thermal and chemical stabilities in recent times. In this study, SiAlON:RE (RE = Rare earths) oxynitride phosphors with compositions of RExSi6-zAlzOzN8-z were successfully prepared using GPS (gas pressured sintering) process. The phase purity, microstructure, luminescent and thermal quenching properties for the prepared SiAlON:RE phosphors were investigated in detail. The obtained SiAlON:RE phosphors had a rod-like morphology with a uniform size of 3-5 micrometer in length and 0.5-1 micrometer in diameter. The SiAlON:RE phosphors absorbed UV-visible spectral region, and showed a single intense broadband emission in visible range. The effects of the RE doping concentration (x) and Si/Al ratio (z) on the optical properties for the SiAlON:RE were discussed under consideration of concentration quenching and nephelauxetic effect. The temperature dependence on photoluminescence (PL) properties was investigated from 300 to 550 K, and the activation energies for thermal quenching of the prepared SiAlON:RE were determined by Arrhenius fitting. The experimental results clearly indicates that the prepared SiAlON:RE phosphors have great potentials as a down-conversion green phosphor for white light emitting diodes (LEDs) utilizing near UV or blue LEDs as the primary light source. R2-S5.24 Embedding (passive components) technology for high integrity built-in devices and further for high density mounting has made LTCC (low temperature cofired ceramics) as promising material for that. In this study, green sheet with structure of 'Al2O3/LTCC/Al2O3' was sintered with 'pressure assisted sintering' technique. As LTCC, commercial powder of 'MLS-22C' was used. Shrunken thicknesses of LTCC layer were measured with variation of pressure load. Shrunken edge curvatures of LTCC layer between constraining Al2O3 layers after sintering were also measured with variation of LTCC sheet thickness at fixed pressure. These curvatures were thought to be responsible for z-axial shrinkage behavior. Optimal sintering conditions of pressure load and LTCC sheet thickness were sought at maximum sintered density, minimum x-y axial shrinkage, and maximum z-axial shrinkage for zero-shrinkage substrate. R2-S5.26 SiCN thin films and Cu/SiCN/Si structures were fabricated through magnetron sputtering. And the rapid thermal annealing(RTA) processing were undergoing for some thin-films samples. The thin-films surface morphology, crystal structure and electronic properties were characterized by Atomic force microscopy(AFM), X-ray diffraction(XRD), Alpha step IQ profiler and Four Point Probe(FPP). The results show that the as-deposited SiCN thin-films were amorphous structure, and their crystallization temperature is upon 1000?. The Cu/SiCN/Si structure has a good thermal stability, and the SiCN thin-films are still able to prevent the diffusion reaction between Cu and Si interface after 5min RTA processing at 600?.
Key words SiCN thin-films, magnetron sputtering, Dielectric diffusion barriers, Cu interconnect for ULSI R2-S5.27 The miniaturization of electronic components has been rapidly spreaded with development of mobile communication. And broadband, multimedia communication strongly needs the electronic components for high frequency band. With this trend, multi-layered ceramic components are mainly used among these components due to their low loss dielectricity at high frequency. Multi-layer ceramic components are fabricated by lamination of tape-casted sheets. Though most slurries for casting have been generally prepared by ball-mill, the ball-mill is frequently replaced with high energy mill such as basket mill to obtain more homogeneous slurries in less time. In this study, two kinds of sheet were fabricated by ball mill and basket mill respectively with change of binder content and plasticizer/binder ratio. Sheet properties such as elongation, tensile strength, density were measured. And also top and bottom surfaces of sheet were analyzed by SEM, AFM, and FTIR. These measured and analyzed values were compared. R2-S5.28 Ferroelectric films with thickness less than 10 nm have recently been the focus of both experimental and theoretical efforts to address fundamental questions about size effects on ferroelectricity. Due to the collective nature of ferroelectric phenomena, ferroelectric material properties are expected to change below a critical film thickness. Although, measuring the switchable polarization by electrical characterization techniques provides the most direct and quantitative probe of ferroelectricity, very large leakage currents in ultrathin PbTiO3 films present require the adoption of alternative methods to measure polarization. Measurements of the unit cell's tetragonality, which is an indirect measure of the spontaneous polarization, implies the existence of a critical thickness below which ferroelectricity vanishes [1]. Recent in-situ synchrotron x-ray scattering studies, which utilized the existence of 180o polar domains as a direct evidence of ferroelectricity in ultrathin PTO films, have demonstrated that, at elevated temperatures, PTO layers are ferroelectric down to 3 unit cells (1.2 nm) [2]. While it has been suggested that a variation in the domain periodicity at elevated temperatures originates from a change from an unscreened to a screened ferroelectric surface, it yet remains unclear why ferroelectric domains cannot be observed at room temperature using synchrotron radiation.
We demonstrate that the laboratory x-ray sources allow the study of ferroelectric stripe domains in ultra-thin PbTiO3 films yielding to the results that are in contrast to the ones obtained from reported synchrotron experiments. We observe the evidence of ferroelectric stripe domains, rather than the mono-domain state, at room temperature for film thicknesses of 1.6 nm to 25 nm. A distinct change in the domain period vs. film thickness relation observed in our study is correlated to a reduction in PTO tetragonality, suggesting that the polarization is constant for films thicker than 10 nm and decay for film thicknesses of 10 nm and less.
Our study shows a distinct dependence of the ferroelectric properties of thin PTO films on the light exposure such as synchrotron radiation and ultraviolet light. Considerable change in stripe domain periodicity was observed after PTO films were exposed to synchrotron x-ray radiation or ultraviolet radiation. A comparative study of the ferroelectric domain behavior at room temperature by a laboratory x-ray source and by synchrotron light with different exposure times suggests that the reported previously mono-domain state in ultrathin PTO films at low temperatures might have been caused by a prolonged exposure to synchrotron radiation, which appears to alter the domain configuration in this temperature range.
1. C. Lichtensteiger, J.-M. Triscone, J. Junquera and P. Ghosez, Phys. Rev. Lett. 94, 047603 (2005).
2. D.D. Fong , G. B. Stephenson, S. K. Streiffer, J. A. Eastman, O. Auciello, P. H. Fuoss and C. Thompson, Science 304, 1650-1653 (2004). R2-S5.29 The magnetic phase transition and magnetic entropy change of melt-spun LaFe11.6Si1.4Bx(x=0, 0.3, 0.5, 0.7) ribbons were investigated by measuring the magnetization as the function of the temperature. Comparing with LaFe11.6Si1.4, the NaZn13 - type structure of LaFe11.6Si1.4Bx(x=0-0.7) did not change after introducing B atoms, while the amount of ?-Fe phase in the ribbons decreased significantly. The Curie temperature changed slightly after the addition of B. The LaFe11.6Si1.4Bx(x=0.3, 0.5) compound exhibited a first - order magnetic transition and a very large magnetic entropy change, which was also observed in LaFe11.6Si1.4 compound, but the later compound was obtained by a longer holding time at high temperature. R2-S5.31 Ceramic radiator fins were produced by screen-printing copper paste on ceramic substrate, which could replace the traditional technique of direct bestrow copper and meet the requirements of surface mounted technology. This method could be used to manufacture high density, superior thin and micro-sized molectrons. The key processes were screen-printing copper paste, sintering and electroless plating of nickel. The adhesion of copper film onto the ceramic substrate was often reduced after the process of electroless plating of nickel, resulting in the low quality of manufacturing. In this study, we analyzed the ceramic radiator fins which were obtained by the screen-printing copper paste method and using scanning electron microscopy to examine the surface and the cross-sections of copper film and Cu/Ni film. The adhesive properties of copper film during electroless plating was studied. The corrosion resistance of copper film and sintering glass phase on alumina substrate (96%) was also studied in an electroplating bath. The study revealed that the glass phase of acidity of silicon, softening temperature, the interaction conjunction between glass phase and ceramics were important factors.
Keywords: copper paste; electroless plating of nickel; glass phase; adhesion 11:00 AM *R3-S2.1 (invited) Magnetic recoding is still the best way for volume data storage and the capacity needs demand higher areal density. As areal densities of commercial magnetic recording progressed beyond 300Gb/in2 [1], the advantages of combining high sensitivity TuMR read head and high writability PMR write headbecame increasingly significant to meet the requirements of the writability and single-to-noise ratio . In this regard, these two recent head technology breakthroughs are the key enablers to keep the current annual compound growth rate of areal density at 40% in HDD industry towards 1Tbit/in2 [2]. In this presentation we will present 520Gbit/in2 results with more detailed discussion and give some perspectives on the 1Tbit/in2 recording sensor.
Advanced TuMR reader and PMR writer were integrated for the performance demonstration. Parametric recording study of these TuMR perpendicular recording heads was performed on the PMR media. Results showed the write heads have strong write field yielding 35 to 45 dB reverse overwrite at narrow magnetic write width of 85 - 115 nm. The read heads also showed large signal amplitude exhibiting high non-disk signal-to-noise ratios of around 24-28 db over a large bandwidth of 450MHz. In addition, close to zero positive-to-negative peak asymmetries were observed and low NTLS of -10 dB was achieved. Regarding to track resolution, microtrack profile showed magnetic track widths as narrow as 40 nm were achieved. Using industry standard testing condition a linear density of 1418KBPI and 366 KTPI was achieved which is at 520Gb/in2. More analysis indicated that TMR heads can support 1Tbit/in2 recording.
References:
[1] S. Mao et al, "Commercial TMR heads for hard disk drives: Characterization and extendibility at 300 Gbit/in2", IEEE Tran. Magn., 42, 97-102, (2006).
[2]. S. Mao et al, "Design and Challenges for 1Tbit/in2 Reader", PMRC 2007 (Oct. 2007, Tokyo, Japan). 11:15 AM *R3-S2.2 (invited) Nanomagnetic systems are finding increasing application in novel storage, sensing and actuation devices. As dimensions shrink so the magnetic behaviour is governed both by the shape and size of the magnetic structure and the intrinsic properties of the material itself. Thus domain and domain wall (DW) structures both change as the films of interest become thinner, are present in laminated form or are geometrically restricted to dimensions of 100's of nanometres or less. The property changes can be beneficial, resulting in new or improved functionality. Equally, unwanted DWs may be generated, introducing additional noise that offsets the advantages that otherwise accrue. In this presentation I illustrate both desirable and adverse effects of trying to tailor magnetic properties towards specific applications. The principal experimental technique used is Lorentz imaging using the transmission electron microscope. This allows direct observation of the domain and DW structure and the way they change under an external stimulus such as applied magnetic field, spin-polarised current or heat pulse.
The DWs themselves can act as information carriers in magnetic nanowires. However, there exist quite different DW structures (vortex DW, transverse DW) that are near-degenerate in energy, resulting in non-reproducible behaviour unless precautions are taken. Moreover transformation of the DW types, at pinning sites along the wire or simply as a result of local microstructural variation, is frequently observed. The detailed structures of some commonly observed walls will be elucidated and examples given of the way the structure can change during DW propagation and depinning given.
The tip region of the write head in a hard disc drive can be likened to a short magnetic nanowire although in this instance the tip is connected to a substantial core (micron sized). To gain insight into how tip and core interact, we have fabricated multiscale planar elements and observed how the domain structure in the core influences the switching of the tip. The structures have been fabricated from high moment CoFe films of the kind used in write heads, and we have studied both single layer and laminated films. Motivation for this is provided by the fact that for a given total magnetic film thickness, laminated films can show better magnetic properties. However, the domain structure that forms in the core differs with the degree of lamination and reproducibility of behaviour in the tip region depends very much on the presence or absence of DWs in the region where core and tip meet. Examples of different reversal mechanisms observed, together with an explanation of their likely effect on device performance, will be given. 11:30 AM *R3-S2.3 (invited) Magnetic nanostructures are attracting considerable interest due to their unique properties and potential applications. Nanomagnets are of scientific interest both from a fundamental viewpoint and also due to their potential in a wide range of emerging applications. Magnetic nanostructures, by virtue of their extremely small size possess both static and dynamic properties which are quantitatively and qualitatively very different from their parent bulk material. A major challenge for technological applications utilizing arrays of magnetic nanostructure is the precise control of the magnetic switching processes. This is directly linked to the quality of the nanomagnets and an understanding of the reversal mechanism with geometrical parameters such as shape and size. The fabrication of high quality, large area magnetic nanostructures is a major challenge in nanomagnetism research. This talk will focus on the use of Deep Ultra Violet (DUV) lithography technique in fabricating arrays of magnetic nanostructures of varying geometrical parameters over a large area. Using resolution enhancement techniques such as alternating phase shift and chrome-less phase shift masks, arrays of ferromagnetic nanostructures with lateral dimensions below the conventional resolution limit have been fabricated. In addition, results of systematic investigations of magnetic spin states evolution, in-plane anisotropy and magnetostatic interaction in arrays of elongated Ni80Fe20 rings and their derivatives will be presented. The magnetization reversal mechanism, the switching field distributions and the transition fields between different magnetic configurations will be shown to be strongly dependent on the inter-ring spacing, film thickness and the missing segment of the ring. A comprehensive investigation of the spin states and magnetic anisotropy in magnetic anti-dot nanostructures will also presented. Detailed magnetization reversal reveals a very strong pinning of domain walls in the vicinity of the anti-structures, the strength of which was found to be strongly dependent on the anti-structure geometry and field orientation. Our understanding of the reversal process is facilitated by micromagnetic modeling. 11:45 AM *R3-S2.4 (invited) For more than a century, ferromagnetic transition, from which ferromagnetism is engendered, has been considered to involve purely an ordering of magnetic moment, without any change in the host crystal structure or symmetry.However, the existence of magnetostrictive effect in all known ferromagnetic systems indicates that the magnetic moment is coupled to the crystal lattice; hence there is a possibility that magnetic ordering may cause a change in crystal structure. So far, such a possibility has been suggested only theoretically, and there has been no direct structural evidence showing a change of crystal symmetry upon ferromagnetic transition. Here we show, with high-resolution synchrotron x-ray diffractometry (XRD), two well-known "cubic" ferromagnets, CoFe2O4 and Terfenol-D (Tb0.3Dy0.7Fe2) are not cubic, but are of a lower symmetry determined by their spontaneous magnetization direction. In-situ XRD observation revealed that the switching of magnetic domain is also a switching of the non-cubic crystallographic domain. Our findings suggest that magnetic transition is also a structural transition like a ferroelectric transition or a ferroelastic transition, although the associated structure change is usually too small to detect by conventional method. The discovery of the structural part of ferromagnetic transition leads to a simple mesoscopic explanation for the generally observed magnetostriction, and may provide new clues for developing highly magneto-responsive materials. 12:00 PM *R3-S2.5 (invited) We at Sirtex Medical Limited have been working for some time on the development of a method for the treatment of liver cancer by Targeted Hyperthermia Therapy using magnetic microspheres exposed to a high frequency magnetic field. The therapy draws on many of the concepts and ideas that form the basis of Selective Internal Radiation Therapy (SIRT). In SIRT, radioactive microspheres, such as SIR-Spheres®, are used to embolise the capillary network surrounding target tumours via infusion through a catheter placed in the hepatic artery. This method of microsphere mediated, targeted radiation treatment is now well established clinically. Targeted Hyperthermia Therapy (THT) is still at the pre-clinical phase but has appeal because of its inherently increased safety profile and lack of complications due to radioactive half life of the therapeutic agent.
Earlier animal studies have established the therapeutic potential of THT and have also highlighted the benefits of using intra-arterially administered microspheres as the heat delivery vehicle. However, the technological difficulties associated with developing a system suitable for clinical use are not to be underestimated. There are a number of constraints, for example the strength and frequency of the magnetic field that can be safely used and the number of microspheres that can be realistically delivered to the tumour, that impose demanding requirements on the heating capabilities of the microspheres.
Working out how to maximise the heat from our microspheres subject to the imposed magnetic field restrictions has been the focus of our research in recent times. Our approach has been to develop polymer microspheres of approximately 32 micron diameter, similar to SIR-Spheres, loaded with a high volume fraction of much smaller magnetic nanoparticles. We have found that the desire to load as much magnetic material into each microsphere competes directly with the deleterious effects of magnetic interactions. The development of strategies aimed at reducing the impact of interaction effects between nanomagnets whilst at the same time enabling a high volume fraction of nanoparticles to be dispersed throughout the polymer matrix is an ongoing theme of this groups work. 12:15 PM *R3-S2.6 (invited) The reason why a certain material is being studied is that the material is either interesting or useful. Quite exceptionally, some layered Co oxides are interesting AND useful. A peculiar feature of Co oxides is that Co ions exhibit different functions for different valences. For example, a tetravalent Co4+ ion in the low spin state causes a large entropy and thermopower in some layered Co oxides. An electron on a divalent Co2+ ion in the high spin state forms a small polaron to show a charge segregation/charge ordering. The spin state transition/crossover of the Co3+ ion from the low-spin to high-spin state.
Here we will briefly look at three layered Co oxides that are interesting and useful: (1) good thermoelectrics in NaxCoO2, (2) unconventional dielectrics in Bi2Sr2CoO6+d, and (3) two-stage spin valve in SrCo6O11. LUNCH 12:30 PM - 2:00 PM 2:00 PM *R3-S3.1 (invited) The AxCoO2
systems (A = Li and Na) have attracted much attention as superb
battery materials (A = Li), as efficient thermoelectrics (A
= Na), and--subject to water incorporation--as superconductors. The CoO2 phase is the parent of the AxCoO2 systems, and we have realized strictly single-phase bulks of not only the CoO2 phase but the LixCoO2 phases by means of an electrochemical technique for de-intercalating Li from LiCoO2. The completely de-intercalated, i.e. x = 0, sample was so pure that the physical properties were revealed to be singular compared to those of other LixCoO2 with x > 0. Although the magnetism of such a CoO2 crystal is anticipated to be magnetically frustrated since every cobalt site in the triangular lattice is occupied by a magnetic CoIV (with S = 1/2), the end member, CoO2 was found from magnetization and 59Co-NMR measurements to be a paramagnetic metal with no signatures of electron correlations, while Li0.12CoO2 was recognized to be a magnetically-correlated metal. Moreover magnetic anomalies were detected for LixCoO2 samples with x = 0.50 (= 1/2) and 0.67 (= 2/3), which indicates the existence of different phases about the compositions. 2:15 PM R3-S3.2 The Transverse Susceptibility (TS) for an assembly of particles was calculated. From the fit of experimental measurements, the mean anisotropy field, the anisotropy field dispersion and the easy axes distribution (texture) are obtained. TS measurements at 127 Hz and at room temperature were performed using a magnetooptical Kerr effect. The experimental set up is described elsewhere [1]. Samples' microstructure was analyzed by x-ray diffraction (XRD) and Atomic Force Microscopy (AFM). Two systems were studied. On the one hand, continuous polycrystalline 1000 ? thick FeCoV thin films deposited by rf sputtering on glass substrate at room temperature. The samples grew in the disordered bcc phase. The films were annealed in a vacuum furnace with a rotating magnetic field. In order to check the validity of the model, the results obtained from the fit before and after annealing were contrasted with structural results. On the other hand Co nanoparticles were grown on Si3N4 substrates by triode sputtering at 550 ° C to investigate the role of thermal relaxation effects on the observed magnetic anisotropy. XRD measurements show that Co mainly crystallizes in its hexagonal metallic phase without texture. AFM measurements revealed a well-defined nanostructured pattern without coalescence. Samples with mean particle diameter of 12 and 15 nm were studied. Regarding the theoretical calculations, a log-normal distribution was taken for the anisotropy field. A double Gaussian distribution was taken for both in-plane and out-of-plane easy axis distributions. The calculated TS reproduces the experimental data with high accuracy. As for FeCoV thin films, we observed a decrease of both the anisotropy constant and the magnetic anisotropy dispersion after annealing (the values being consistent with that of bulk bcc Fe50Co50). The lattice constant obtained from XRD approached the bulk value after annealing. So a higher contribution to magnetic anisotropy from stress is expected in the as-deposited sample, which explains the evolution of the magnetic anisotropy and its dispersion. Regarding the texture we obtained an increase of the in-plane easy axis standard deviation after annealing, which may be explained as due to the rotating magnetic field. Regarding Co nanoparticles, the mean anisotropy field obtained from the fits was 31 Oe and 22 Oe for mean particle diameter of 12 and 15 nm respectively, too low to be identified with hcp Co magnetic anisotropy. In this case thermal relaxation affects very strongly the value of the effective anisotropy observed, yielding an effective magnetic anisotropy lower than expected [2].
[1] M. C. Contreras, J. F. Calleja, M. Rivas, M. O. Guti?rrez and J. A. Corrales, J. Magn. Magn. Mater. 175. 64, 1997.
[2] L. Spinu, C. J. O'Connor, and H. Srikanth, IEEE Trans. Magn. 37, 2188, 2001. 2:30 PM R3-S3.3 Abstract- This article presents the effect of operated Radio Frequency Identification (RFID) at 125 kHz on GMR recording heads. The study is mainly concerned the RFID effect on recording heads in terms of the distance (Distance) between antenna reader of RFID and recording head, the coil radius (Radius) of antenna reader, and the angle (Angle) between antenna reader and recording head. It is firstly reported that the maximum error of writing current is of about 3% (where r < a). It is found that the erroneous writing current tends to be decreased when the radius and angle increase. This can be mathematically explained by adapted equations. The results undoubtedly agree with industrially electrical test parameters. The SEM is also used to clarify the physical change. 2:45 PM R3-S3.4 Magnetic field induced step-like transport jump is found at low temperature for Pr doped phase-separated manganites. Magnetization measurements indicate that spin-stiffness constant D exhibits large magnetic field dependence. Moreover, there exists a remarkable change of spin-stiffness constant corresponding to the variety of the step-like transport jump. This suggests a possible existence of quantum orbital transfer resulting from the change of orbital ordering (OO) modes and accompanying with spin reorientation and carrier delocalization. The carrier delocalization is closely related to the coupling of charge-orbital and can be proved from the low temperature resistivity minimum behaviour. The phase diagram was determined. These all show the importance of the strong interaction of charge-orbital and/or spin-orbital in the adjacent long-range charge-ordered antiferromagnetic phase, which depends sensitively on the OO modes. 3:00 PM R3-S3.5 A new type of half-metal which is composed by transition-metal mono-pnictides or chalcogenides, such as ZB-MnAs, ZB-CrAs, ZB-CrSb, has attracted increased attention after the theory prediction and experimental fabrication of half-metallic zinc-blende (ZB) CrAs thin films by Akinaga et al. in 2000 [1]. The ZB half metals have high Curie temperature, large magnetic moment, and compatibility with ZB III-V and II-VI semiconductors. However, it was found to be difficult to grow the ZB half-metallic ferromagnetic phases as thick films. Recent report indicated that the CrTe, CrSe, and VTe in the ZB structure are excellent half-metallic ferromagnets with large half-metallic gaps. They also proved that these ZB half-metals are mechanically stable and approximately 0.31~0.53 eV higher in energy per formula unit than the corresponding NiAs ground state phase, which suggests that these ZB half-metals could be grown stable [2]. However, up to now no systematic results show the magnetic anisotropy of this type of half-metal. We have reported the epitaxial growth of ZB-CrTe thin films and the characterization of their large magnetic anisotropy [3]. Furthermore, here, we present the three types of CrTe thin films in different structure conditions: ZB thin films, NiAs-phase films, and CrTe nanoclusters. After the growth, the structures were analyzed using high-resolution transmission electron microscopy (HRTEM) and the magnetic properties were measured by the superconducting quantum interference device (SQUID) magnetometer for three samples. The uniaxial (KU) and cubic (KC) anisotropy constants are obtained through the fitting the magnetization curves respecting the different easy magnetic axis of different samples. The easy axis are [001] for ZB-CrTe thin films, [011] for CrTe nanoclusters, and [0-11] for NiAs-phase CrTe films respectively. It is supposed that the different anisotropy conditions coming from their different intrinsic crystal structure.
reference
[1] H. Akinaga, T. Manago, and M. Shirai, Jpn. J. Appl. Phys. 39, L118 (2000).
[2] W. H. Xie, Y. Q. Xu, B. G. Liu, D.G. Pettifor, Phys. Rev. Lett. 91, 037204 (2003).
[3] J. F. Bi, M. G. Sreenivasan, K.L. Teo and T. Liew, J. Phys. D: Appl. Phys. 41 (2008) on publish. 3:15 PM R3-S3.6 Low density core &oline shell composite powders of hollow glass microspheres (HGMs) coated Co were prepared using electroless method. The composite powders were characterized by scanning electron microscopy (SEM), energy &oline dispersive spectroserpy (EDS) and X &oline ray diffraction analysis (XRD), Vibrating Sample Magnetometer (VSM) to investigate their micro- morphology, element, microstructure and magnetic property respectively. The microwave electromagnetic loss and absorbing properties of HGMs with Co thin films were tested by network vector analysis in the 2 &oline 18GHz frequency range. The results show that the continuous and uniform coatings are deposited on the surface of the HGMs, coatings are composed of Co and the Co film was amorphous structure. The HGMs coated by Co possess the same magnetic property as pure Co, and the saturation magnetization and the coercive force were increased after heat treatment. The reflection loss of core &oline shell composite powder was less than -10 dB in the frequency range of 1.8 &oline 8.2 GHz; the minimum reflection is -26 dB with match thickness 2mm. The strong electromagnetic absorption properties can be explained by the multi-scatter and interface polarization of the special core &oline shell structure. AFTERNOON BREAK 3:30 PM - 4:00 PM 4:00 PM R3-S4.1 FePt nanoparticle is considered to be the best candidate for a high density hard disk for mass storage purpose. A Ru underlayer usually was deposited to stabilize the magnetic properties. To understand the effect of a mixture structure or the interface of Ru and FePt is of important in the future hard disk fabrications. In this work, we prepare the FePt nanoparticles by heating the mixture of two precursors, platinum acetylacetonate and iron pentacarbonyl, in the presence of oleic acid and oleylamine stabilizers at 570 K. Ru atoms was doped by adding the Ru acetyacetonate. The samples were studied by XRD, TEM, EDS and X-ray absorption spectroscopy (XAS). The magnetic property was measured by SQUID. The resulting particle size is around 5 nm and the composition of Fe:Pt is heavily dependent on the procedures of adding the Ru precursors. For the ternary alloy with Fe:Pt around 1:1, the magnetic result shows that the addition of Ru of less than 5% does not change magnetic properties of FePt nanoparticles. The phase transition temperature for the as-grown FCC FePt nanoparticle to be transformed into L10 ordered FePt nanoparticle is about 880 K which is the same as the one without doping Ru particles. XAS study shows that the Ru atoms, although with the size close to the Pt, do not replace the Pt sites in the FePt alloy. A shell structure might be formed. 4:15 PM R3-S4.2 for realizing spintronics devices which combine microelectronics with spin-dependent effects that arise from the interaction between spin of the carrier and the magnetic properties of the material. The application of non-equilibrium growth methods such as molecular beam epitaxy (MBE) has been demonstrated to offer doping in excess of the thermodynamic solubility limit [1,2]. However for many semiconductor materials, the bulk solid solubility of magnetic or electronic dopants is not favorable for the coexistence of carriers and spins in high densities. In this aspect, IV-VI ferromagnetic Ge1-xMnxTe is an interesting material to study because it has been reported to have a high solubility limit of more than 95% Mn in GeTe and a highest Curie temperature of Tc = 140K [3]. So far, a comprehensive understanding of the magneto-transport behavior of this material has not yet been achieved. In this work, we conduct the temperature dependent magneto-transport studies on a Ge1-xMnxTe film with high Mn composition of x = 0.98 prepared on BaF2 (111) substrate using a MnTe buffer layer by solid source MBE technique.
The M-H curves of the Ge0.02Mn0.98Te film were measured at 5 K with field applied in-plane (H || plane) and perpendicular to plane (H ⊥ plane). We did not observe distinct magnetic anisotropy for different applied-field directions as the difference in coercivity is very small, ΔHc ~ 27Oe. The ratio of Mr(||)/ Mr(⊥) increases from 1.44 at T = 5 K to 2.58 at T = 90K, where Mr(||) and Mr(⊥) are the in-plane and perpendicular remanences, respectively. Our temperature dependence of coercive fields in the two cases is nearly the same. The result indicates that the magnetic moments are not all in-plane but part of them are out of plane. The existence of the out-plane magnetic moments could be due to surface roughness which may induce spin disordering in the film surface. As the temperature increases, the disordered spins are randomized, therefore the out-plane magnetic moments are enhanced at near the Tc. Magnetoresistance (MR) measurements were performed with (H || plane) and (H ⊥ plane) from 20 to 120 K. A negative MR was observed for all temperature range for (H || plane). For (H ⊥ plane), the MR is entirely negative for T < 75 K. The disappearance of the negative MR above T ? 95 K could be represented as a transition from ferromagnetism to paramagnetism at Tc = 95K which is consistent with our M-T curve results.
References
[1] H. Ohno et al., Appl. Phys. Lett. 69, 363 (1996).
[2] Munekata, H., H. Ohno, S. von Moln?r, A. Segm?ller, L. L. Chang and L. Esaki, Phys. Rev. Lett. 56, 777 (1989).
[3] Y. Fukuma, T. Murakami, H. Asada, and T. Koyanagy, Physica E (Amsterdam) 10, 273 (2001). 4:30 PM R3-S4.3 Interlayer magnetic coupling between ferromagnetic layers separated by nonmagnetic spacer layers have been investigated to a large extent, because it can cause the spin-dependent scattering of conduction carriers, which is exploited for the giant magnetoresistance effects. Since the semiconducting spacer has a potential to be changed it electric state, by irradiating or heating , the resultant change in magnetic coupling among ferromagnetic layers receives a much attention not only from the physical point of view but also from the technological one.
Fe-Si system has a variety of phases such as the semiconducting β-FeSi2 and nanocrystalline (NC) FeSi2, and ferromagnetic Fe3Si and Fe. The Fe/Si and Fe/Fe1-xSix superlattices have been studied until now. Compared to these, the Fe3Si/FeSi2 superlattices have following merits: i) the electric conduction mismatch between them is within an order of magnitude; ii) the d- electrons contribute to the electric conduction in both layers. The heterostructural film using these phases is expected to be a new candidate for the spintronics.
[Fe3Si(25 Å)/NC-FeSi2(X Å)]20 superlattices were deposited on Si(111) at an elevated substrate temperature of 300 °C by facing targets DC sputtering. The magnetoresistance ratio and interlayer coupling strengths were enhanced by approximately 100% and 34%, respectively, as compared to those of superlattices deposited at room temperature [1]. While the elevated substrate temperature degraded the interface sharpness, the crystalline orientation and the crystallinity of the Fe3Si layers were apparently enhanced. The latters strongly influence on the interlayer coupling and the magnetoresistance ratio. This implies that quantum well states are tightly formed under the well-ordered crystalline planes, and the spin diffusion lengths are improved due to the enhanced crystallinity.
[1] T. Yoshitake, T. Ogawa, D. Nakagauchi, D. Hara, M. Itakura, N. Kuwano, Y. Tomokiyo, K. Takeda, T. Kajiwara, M. Ohashi, G. Oomi, and K. Nagayama, Appl. Phys. Lett. 89, 253110, 2006. 4:45 PM R3-S4.4 Owing to recent intensive studies, many diluted magnetic semiconductors (DMSs) with high Curie temperature have been discovered [1]. However, the origin of gnetism observed in the DMSs is very controversial. A difficulty in understanding the mechanism responsible for the observed magnetism is that DMSs samples prepared by different techniques could span the entire spectrum of possibilities from single-phase random alloys to nanoclusters of the magnetic atoms to precipitates and second-phase formation [2]. This problem can only be solved by correlating the measured magnetic/spintronic properties with materials characterizations that are capable of detecting other phases and precipitates. Therefore, in order to deepen our understanding of the origin of the magnetism of the new DMSs [3,4] a major priority is to explore and apply element- and position-specific analytical techniques for characterisation of this new class of materials.
Among various characterization techniques, atom probe tomography (APT) [5] could be the most powerful technique to solve the current problem in DMSs research. APT is capable of mapping the chemical identity and the 3-dimensional position of individual atoms within a sample with single atom depth resolution and sub-nanometer lateral resolution. After APT data is reconstructed, many statistical analyses can be applied to determine the exact distribution and relationship of the magnetic ions and semiconductor matrix.
In this presentation, we report the results from APT studies of DMSs.
[1] V. A. Ivanov, T. G. Aminov, V. M. Novotortsev et al., Russ Chem B+ 53, 2357 (2004).
[2] S. J. Pearton, W. H. Heo, M. Ivill et al., Semicond Sci Tech 19, R59 (2004).
[3] S. J. Pearton, W. H. Heo, M. Ivill et al., Semicond Sci Tech 19, R59 (2004).
[4] S. J. Pearton, Y. D. Park, C. R. Abernathy et al., J Electron Mater 32, 288 (2003).
[5] M. K. Miller, Atom probe tomography : analysis at the atomic level. (Kluwer Academic / Plenum Publishers, New York, 2000). 5:00 PM R3-S4.5 Electrostatic discharge (ESD) effect on GMR recording heads have been reported for the major cause of head failure. Since the information density in hard-disk drive has dramatically increased, the GMR head will be no longer in use. The tunneling magnetoresistive (TMR) read heads are initially introduced for a 100 Gbit/in2 density or more. Though the failure mechanism of ESD in GMR recording head has not been explicitly understood in detail, the study to protect this effect has to be undergone. As far as the TMR head has been commercially started, the ESD effect is closely aware. This is the first time report on the TMR equivalent circuit in order to evaluate the ESD effect. A standard human body model (HBM) is discharged across R+ and R- where the capacitances of flex on suspension (FOS) are varied. It is intriguingly found that electrical characteristic of TMR head during discharge period depends on discharge position. This may be explained in term of asymmetry impedance of TMR by using adapted Thevenin's theory. The effect of FOS component on TMR recording head is also discussed. 5:15 PM R3-S4.6 Electrostatic Discharge (ESD) effects have been alert as one of the most dangerous cause of GMR recording head damages. These phenomena have been studied in all level of hard-disk drive manufacturing [1]. The Head Gimbal Assembly (HGA) is mainly studied because of its exposure to environment. The standard models are typically based on human body model (HBM), charged device model (CDM) and machine model (MM) where research and practical tests are incompatible. In production, one or more ESD models are normally effective while the other is undergone under a separated model. In addition, tests in time domain are more accurate than those in frequency domain. However, picosecond measuring equipments are taken in difficulty where the frequency domain measurement provides non-real time results. Therefore, this is firstly reported the serial ESD detection by using a new technique of wavelet transform. It is found that this newly proposed technique, of the 4th Daubechies wavelet transform, provides undoubtedly better results that the conventional ones. The most intriguing results found in time-delay of each model input. The SEM result is shown to confirm the experiment.
This research is funded by the Thailand Research Fund, Grant No. RMU4880033. The authors would like to express thankfulness to Western Digital (Bangpa-In), Co. Ltd., for providing samples and facilities.
[1] A. Siritaratiwat, D. Tongsomporn, K. Chooruang and N. Afzulpurkar. IEEE Transactions on Magnetics 2005: 41; No. 10; p. 2941-2943. 9:00 AM *R4-S1.1 (invited) PDMS-based conducting composite and its application in micro-electronic fabrications
Weijia Wen
Department of Physics and Institute of Nano Science and Technology
The Hong Kong University of Science and Technology
Clear Water Bay, Kowloon, Hong Kong
Abstract
We report a fabrication approach to construct conductive microstructures embedded in polydimethylsioxane (PDMS) bulk material. The conducting composites are synthesized by mixing nano or micro size conductive particles with PDMS gel. The experiments show that such composites exhibit good conductivity and mechanical reliability. By using this kind of composite, we are able to construct planar and three-dimensional microstructures by soft-lithographic technique. The realistic applications for three-dimensional microstructure in the wiring connections, micro-heater, flexible paper-like display as well as other devices are presented and the result obtained is very promising for the utilization of such composites in future micro-fabrications. 9:15 AM *R4-S1.2 (invited) We report the successful synthesis and the magnetic and dielectric properties of a novel perovskite oxide, BiMn7O12-δ. The new phase is obtained by high-pressure synthesis and it possesses a strongly distorted monoclinic perovskite structure with space group I2/m and the lattice parameters, a = 7.548 ?, b = 7.393 ?, c = 7.556 ?, and ? = 91.23 degrees. In this structure the A-site cations, Bi3+ and Mn3+, are ordered in a 1:3 arrangement. In magnetization measurements two magnetic transitions were detected, a weak FM transition at 59 K and an AFM transition at 28 K. The phase shows both positive (below the lower magnetic transition temperature) and negative (about both the lower and the higher magnetic transition temperatures) magnetocapacitance effects, and electric-field-induced ferroelectricity-like behaviour below 81 K. The magnitude of spontaneous polarization was found to increase upon applying a magnetic field, thereby indicating a magnetoelectric coupling to make BiMn7O12-δ a candidate for multiferroics of a novel type. 9:30 AM *R4-S1.3 (invited) The lead (Pb) content of Pb-based piezoceramics has recently raised
environmental concern, and has created motivation to find a Pb-free replacement
with comparable characteristics and simple perovskite structure. Though some
guidelines which predict the presence of MPBs do exist, comprehensive mapping
of compositions requires synthesis of an enormously large number of individual
samples. We overcome this challenge by implementing a combinatorial
synthesis strategy, where we have identified a property enhancing morphotropic
phase boundary (MPB) in the (Bi,Sm)FeO3 system, whose electromechanical
properties represent substantial enhancement over those of simple BiFeO3. We
show a rhombohedral to triclinic to orthorhombic structural transition which
exhibits a ferroelectric (FE) to antiferroelectric (AFE) transition at the MPB
with piezoelectric properties comparable to those of PZT thin films. Thus the newly
discovered MPB sits at an interesting ferroelectric/antiferroelectric transition,
and as a consequence we also demonstrate characteristics of a new Pb-free
antiferroelectric.
The authors would like to thank all the technical officers from the Electron Microscope Units at UNSW and University of Sydney from their generous guidance and Prof. Ray Withers (Australia National University) for the bond-valence computations. Research at UNSW was supported by an ARC Discovery Project DP0666231 and a DEST ISL grant. Work at Maryland was supported by access to the Shared Experimental Facilities of the UMD-NSF-MRSEC (DMR 0520471), NSF DMR 0603644, and ARO W911NF-07-1-0410. The work was also supported by the W. M. Keck Foundation and NEDO. 9:45 AM *R4-S1.4 (invited) Functional relaxors, such as relaxor dielectrics and relaxor ferroelectrics, are promising tuneable microwave component materials as a result of the electric field and frequency dependence of their dielectric permittivities. Relaxors of this type have been known for over half a century. The relaxation mechanisms underlying their unique dielectric behaviour, however, are still far from well understood. This lack of understanding provides a significant impediment to the further development and optimization of their desirable dielectric properties (high dielectric constants, low dielectric losses and high field tuneabilities) to meet the demands of the emerging commercial market. Because such functional relaxors are almost invariably structurally disordered, the key to understand their dielectric properties is an understanding of their local nanoscale crystal structure.
Electron diffraction is extremely sensitive to weak features of reciprocal space such as structured diffuse scattering arising from local nanoscale ordering and associated structural relaxation as a result of the strong interaction of electrons with matter. Recent such work in our group has successfully explored local crystal structure in both bismuth-based pyrochlore relaxor dielectrics and BaTiO3-based relaxor ferroelectrics.
In bismuth-based pyrochlore electroceramic systems with average structure space group symmetry of Fd-3m, three distinct types of local structure have been observed. The local crystal chemical ordering and associated structural relaxation of these have been interpreted and understood with the use of Monte Carlo simulation and neutron powder diffraction refinement. This has enabled the relationship between local structure and dielectric properties to be discussed.
In BaTiO3-based relaxor ferroelectric systems, the observation via electron diffraction of relatively sharp, G ? {001}* sheets of diffuse intensity arising from the large amplitude excitation of inherently polar, transverse optical modes of distortion, shows that the 1-d polar nano regions (PNR's) responsible for the observed dielectric behaviour of these relaxor ferroelectric materials correspond to the same highly anisotropic <001> chain dipoles as are characteristic of the cubic paraelectric phase of BaTiO3 itself. The role of the dopant ions is not to directly induce the 1-d PNR's but rather to set up random local strain fields preventing the condensation of long wavelength homogeneous strain distortion of the unit cell thereby suppressing transverse correlations of the <001> chain dipoles and the development of long range ordered ferroelectric state/s. 10:00 AM R4-S1.5 One of potassium niobate crystals denoted as KNbO3 (KN) has been famous for ferroelectric and piezoelectric crystals. It has been difficult to grow bulk single crystals from melt because of incongruent melting and two times solid-state phase transformations, such as cubic /(708 K)/ tetragonal /(498 K)/ orthorhombic structures. In recent years, KN crystal is of interest for piezoelectric applications because of its large electric-mechanical coupling factor more than 50 % and zero temperature coefficients near room temperature. These are reported by theoretical and experimental approach. The common growth method of KN in bulk shape is Top Seeded Solution Growth (TSSG) method. It is reported that Bridgman (BM) method is more easy method than TSSG method to grow KN crystal. It is still difficult to grow large size and high quality crystals. Thus, KN crystal has been grown with high quality and low lattice defects in fiber shape.
On the other hands, Na doping has been carried out on KN thin films in recent years. By the Na doping, the piezoelectric properties are improved. However, Na doping is reported to be effective only on thin films not on single crystals. It is because the composition of grown single crystals will be changed by the difference of ionic radius, i.e., Na ion is too small. We consider that it will be improved this difficulties by the doping of large Rb or Cs ions as co-dopant.
In the present work, we tried to grow K-Na-A (A: Rb, Cs) niobate single crystals in fiber shape by our original pulling down technique with orthorhombic phase, and investigated their electric properties for the characterization. Doping amounts of Na and A are up to 10-20 mol% in K-Na-A (A: Rb, Cs).
Crystal growth method is called Floating zone puling down (Fz-PD) method. For the characterization sample, small pieces were cut perpendicular to the growth direction from the grown crystals. The characterizations were carried out for the change of the lattice volume and the composition, and the electric properties, such as dielectric constant and impedance etc. Ag paste and Au coating were used for electrode fabrication.
By the Fz-PD method, single-phase crystals by Rb doping could be grown in 1-2 mm diameter with fiber shape, but could not be grown by Cs doping. The quality is good by the observation under cross-nicols.
This work was supported by a grant from Futaba Electronics Memorial Foundation. 10:15 AM R4-S1.6 Superconducting technology offers low attenuation of the electromagnetic signals and hence is the most promising material for wireless communications. However the loss in a circuit/device depends not only on the loss of the superconducting material but also on the non-superconducting components used in conjunction with the superconducting components. We have measured the complex permittivity of some of the commonly used planar PCB materials at microwave frequencies and at cryogenic temperatures. For the microwave characterization of material different methods such as are one port coaxial and waveguide cells, open-ended probes, free-space transmission/reflection or reflection methods, microwave microscope methods, microwave cavity methods, stripline and microstrip methods can be used. Split Post Dielectric Resonator technique (SPDR) is proved to the most accurate technique for measuring the electromagnetic properties of thick planar materials such as Printed Circuit Board materials, dielectric and ferroelectric substrates at the frequency range of 1-10 GHz. We will present the cryogenic complex permittivity data of some of the commercially available PCB materials. MORNING BREAK 10:30 AM - 11:00 AM 11:00 AM *R4-S2.1 (invited) The existence of multiple bands in MgB2 leads to new physical phenomena that do not exist in single-band superconductors. It is also a promising superconductor for high-field magnets, electronics, and RF cavities. High quality MgB2 films are critical for electronic applications, and are promising for high field magnets in the form of coated conductors and for RF cavity by coating the interior cavity wall. The Hybrid Physical-Chemical Vapor Deposition (HPCVD) technique has successfully produced epitaxial MgB2 thin films with excellent superconducting and normal-state properties. The pure films are very clean with higher-than-bulk Tc and mean free path limited by the film thickness. The carbon doped films show record-high upper critical field Hc2 values of over 60 T, very attractive for high-magnetic-field applications such as magnetic resonance imaging. Planar MgB2-TiB2-MgB2 SNS Josephson junctions have been made that show excellent properties above 30 K. Trilayer MgB2-barrier-Pb SIS Josephson junctions have been produced that show both π-band and σ-band features and excellent MgB2-barrier interface properties. For coating complex shaped object like RF cavities, the technique of ex situ annealing of CVD-grown B films in Mg vapor has been developed, which has deposited very high quality films. 11:15 AM *R4-S2.2 (invited) The critical temperature and other superconducting properties of a two-band superconductor depend on the doping level and on the interband and intraband scattering. These properties can be modified by chemical substitutions, which change the electronic and defect structures, and thus the superconducting gaps and the inter- and intraband scattering. Of potential practical interest are an enhancement of the upper critical field, Hc2, and a reduction of its anisotropy. However, modifications of these parameters by chemical substitutions in MgB2 are still not well understood. In order to study the influence of doping and intra- and interband scattering on the gap and other superconducting properties, investigations of partially substituted MgB2 are of particular interest. Due to the anisotropic character of MgB2, single crystal studies provide more detailed insight. Hole doping in MgB2 has been investigated very little. We have investigated the effect of hole and electron doping in Li, C, Al substituted, Li-C and Li-Al co-substituted MgB2 crystals. The influence of Mg vacancies has been also investigated. Tc of MgB2 crystals with simultaneously substituted Li for Mg and C for B decreases more rapidly than in the case where C is substituted alone. This means that holes introduced by Li cannot counterbalance the effect of electrons coming from C. The possible reason of it can be that holes coming from Li occupy the ? band while electrons coming from C fill the ? band. In Li-Al co-substituted crystals Tc depends only on Al content. Surprisingly the existence of Mg vacancies up to 8% did not decrease Tc. C substitution as well as C/Li substitution enhanced upper critical fields Hc2. dHc2/dT for Al and Li substituted crystals with the same Tc show a similar slope at Tc and similar Hc2(T) behavior, despite of much different substitution level. The observed features can be explained as a result of two effects, influencing both Tc and Hc2. The first one is doping related to the changes in the carrier concentration, which may lead to the decrease or to the increase of Tc. The second one is related to the introduction of new scattering centers leading to the modification of the interband and/or intraband scattering and, therefore, resulting in changes in the gap structure and in the reduction of Tc. Electrical transport measurements show an increase of resistivity both in Li substituted crystals and in Li and C co-substituted crystals. This indicates enhanced scattering due to defects introduced by substitutions including distortion of the lattice. 11:30 AM *R4-S2.3 (invited) Flux pinning properties by artificially introduced GZO nanorods are investigated for IBAD/PLD-processed GdBCO coated conductors in a magnetic field up to 5 T in the temperature range of 60-80 K. It was found that the critical current density was almost flat with respect to the field angle in a wide magnetic field range, showing remarkable contribution by nanorods to the flux pinning in the magnetic field parallel to the c-axis. The high critical current density in the field angle between the a-b plane and the c-axis is considered to be caused by the pinning by nanorods which are tilted from the c-axis. The contribution to the virtual pinning force density in the creep-free case from the artificial nanorods is calculated using the summation theory of elementary pinning forces, and this is summed with the contribution from natural defects the property of which obeys the anisotropic formula with respect to the field angle. The theoretical critical current density estimated from the calculated pinning force density using the flux creep-flow theory is compared with the experimental results. 11:45 AM *R4-S2.4 (invited) Now after 20 years since the discovery of high-temperature superconductors, practical superconducting wires made of these materials are being manufactured and the verification examinations for electric and industrial applications are being carried out one after another. The high-temperature superconductors have appeared at center stage again as dream materials after a long period of research and development. Here, flux pinning has become very important. The critical current density, Jc, of the superconductor is governed by the strength of the flux pinning. To draw out the high performance of high-temperature superconductors, a new technology for introducing effective pinning centers into superconductors by means of nanotechnology is being developed and is now the focus of attention.
There has been significant progress in research on enhancing flux pinning in YBCO films and YBCO coated conductors due to artificial pinning centers (APCs). Various kinds of APCs can control the flux pinning properties, such as maximum pinning force, magnetic field angular dependence, temperature dependence, and so on. We successfully increased the irreversibility field (Birr) and the Jc-B properties of YBCO films by the technique. The obtained Birr and Jc-B values at 77 K exceed those of NbTi at 4.2 K. The practical YBCO coated conductors that have excellent Jc-B properties at 77 K, superior to NbTi wires at 4.2 K, will be realized in a near future.
Recently we have achieved very large Fpmax (JcxB, over 28 GN/m3, 77 K, B//c) by the newly developed APC method, while Fpmax=5 GN/m3 for the pure YBCO film (77 K, B//c), 13 GN/m3 for YBCO+BaZrO3 nanorods (77 K, B//c) and 16 GN/m3 for the NbTi wire (4.2 K). The Fpmax of the present YBCO films with APCs reached nearly 100 GN/m3 at 65 K (B//c). These amazing pinning forces are due to the high-density strong pinning centers in the films with optimized APC approach.
In this talk, we show our efforts of introducing APCs into YBCO films to increase the flux pinning and of designing APC nanostructures based on the time dependent Ginzburg-Landau (TDGL) simulation combined with Maxwell equation. The example of flux pinning by using TDGL simulation is illustrated in Fig.1. The results indicate that the further increase in Jc can be expected in an optimized APC nanostructure and the nanotechnology would make do-it-yourself flux pinning engineering possible. 12:00 PM R4-S2.5 MgB2 is considered a double gap superconductor, with its Fermi surface to be consisted of 2D σ and 3D π electronic bands. Theoretical calculations show that only the doubly degenerate mode of E2g symmetry, located at energy ~600 cm−1 and involving vibrations of the boron atoms along the ab−plane is expected to be Raman active.
We have carried out a systematic micro−Raman study of the atomic substitution effects in single crystals of MgB2, including Li or Mn doping for Mg, and C doping for B. The spectra of C−doped compounds exhibit remarkable differentiations with respect to pure MgB2, and new bands appear at energies ~750 and ~850 cm−1 for all the substituted compounds. These bands have been identified as A1g/B1g and E2g symmetry bands respectively, according to the applied selection rules. The results are consistent with the data from the Al substitution for Mg and can be explained by assuming a change in the dimensionality of the σ electronic bands from 2D to 3D, and a two−mode behavior for the E2g phonon, possibly associated with a phase separation scenario.
Alternatively, Li (hole) doping does not induce such effects, and only small alterations can be observed in the Raman spectra. Tc is only barely reduced for Li substitution, giving an indication that MgB2 is probably a slightly underdoped material. The data can be explained by assuming that Li doping does not induce a 2D−3D dimensional crossover as in the case of the C or Al doping. Mn doping also leaves the spectra practically unchanged, while only 2% substitution renders the material non-superconducting. In this case, electron−phonon coupling does not seem to be affected and there is a possibility that the magnetic pair−breaking effect due to the magnetic moment of Mn+2 ions is responsible for the rapid suppression of superconductivity. 12:15 PM R4-S2.6 This work presents the study of some new anomalous electromagnetic effects in graphite-like thin carbon films. These are:
* The fast (10-9 sec) switching of electrical conductivity
o The detection of the microwave radiation and its temperature dependence
o The oscillations of the film stack magnetization in the magnetic field of 1-5 T.
o The generation of the optical radiation during the spasmodic switching of conductivity
These effects are explained as the consequence of carbon films granular structure, which can be considered as the Josephson junction array (JJA).
Results of the magnetic force microscopy (MFM), the DC SQUID magnetization, the reversed Josephson effect (RJE), and the resistance measurements in thin carbon arc (CA) chemical vapor deposited (CVD) films are presented. The observation of a RJE induced voltage as well as its rf frequency, input amplitude, and temperature dependence reveals the existence of Josephson-like Junction arrays. Oscillating behavior of the DC SQUID magnetization reminiscent the Fraunhofer-like behavior of superconducting (SC) critical current in the range of 10000-50000 Oe has been observed. The DC SQUID magnetization measurement indicates a possible elementary 102 nm SC loop; this is compared to MFM direct observations of the magnetic clusters with a median size of 165 nm. The results obtained provide a basis for non-cryogenic elecrtonic devices utilizing the Josephson effect. LUNCH 12:30 PM - 2:00 PM 2:00 PM R4-S3.1 (002)NiO was formed by surface oxidation eptiaxy (SOE) of rolling assisted biaxially textured substrates (RABiTS)s of Ni or Ni-alloys. The formation of (002) NiO layer was investigated as a function of oxidation temperatures and time. The properties of the surface oxides on pure Ni and Ni-W were investigated. The formation of smooth NiO on Ni-W was difficult due to the formation of porous internal oxides and also the formation of ternary oxide like NiWO4. The oxidation rate of Ni-W was also magnitudes faster compared to pure Ni which leads to surface oxide cracking and delamination. The mechanism of oxidation of cube textured Ni-W is proposed. Thin film ceria was coated onto NiO|Ni or Ni using chemical solution deposition (CSD) process to produce CeO2|NiO|Ni or CeO2|Ni buffer-substrate system. Nitrate based solutions were used with surfactant like Triton-X was added to the solutions to improve the coating properties. Glycol was also added to the solution to improve on the properties of the coating. 2:15 PM R4-S3.2 Various multilayering in YBa2Cu3O7 thin films is shown to affect different microstructural parameters in the films. These parameters are investigated and linked to the modification of electromagnetic properties in thin films and multilayers produced. The key process regulating the structure occurs at the interfaces during pulsed laser deposition of the films, independent of the origin of these multilayers. Vortex pinning regimes and mechanisms related to the observed defect film environment are considered, and the corresponding quantitative description is developed within the frames of the statistical pinning analysis. The understanding of the direct relationship between film micro- and nano-structures, processes at the interfaces, pinning mechanisms and current-carrying ability enables the controllable adjustment of the thin film behaviour in a particular range of magnetic fields, applied currents and temperatures, which can make it easier adapt this behaviour to certain practical applications.
This work is supported by the Australian Research Council. 2:30 PM R4-S3.3 In this paper, a study regarding the epitaxial growth of CexZr1-xO2 film on biaxially textured Ni-5at.%W substrate and its use as a single buffer layer of a YBCO coated conductors was reported. Films of Ce-Zr mixed oxide were prepared by direct-current (d.c.) reactive magnetron sputtering with the two sputtering guns arranged symmetrically with respect to the substrate. In sputtering process, d.c. power of Zr was fixed in 200 W while that of Ce was varied with 30 W, 50 W, and 100 W, respectively. It was confirmed that the composition of the films could be controlled with controlling power of Ce target. Different deposition conditions were employed and compared in order to obtain good epitaxial CexZr1-xO2 film. Scanning electron microscopy revealed a continuous, dense, and crack-free surface morphology for CexZr1-xO2 thin films, which provided themselves as the good single buffer to the YBa2Cu3O7-? (YBCO) coated conductors. High quality CexZr1-xO2 buffer layers up to 100-m length could be fabricated with production speed of about 1.2m/h. Subsequently, Epitaxial YBCO films grown by d.c. sputtering on the short prototype CexZr1-xO2 conductors were also investigated. 2:45 PM R4-S3.4 The PIT-processed Bi2223 multifilamentary tapes have high performance enough for prototype configurations of power devices such as cables and transformers. However, the loss generation in the tapes under AC operation is still too high for practical applications, because of strong electromagnetic coupling among Bi2223 filaments due to low resistivity of Ag matrix and also because of direct connection among the filaments. An introduction of resistive barriers together with filament twisting with an appropriate pitch is required for making electromagnetic decoupling and also for suppressing bridging among the filaments. The PIT-processed Bi2223 tapes were fabricated either by using the Ag-alloy as the matrix or by introducing oxide barriers (e.g., Ca2CuO3, Al2O3 and SrZrO3), while changing tape width, twist pitch and number of filaments systematically. The AC losses were measured at 77 K as functions of both field amplitude and frequency in parallel and perpendicular fields. For reduction of AC losses, it is shown that an introduction of resistive barriers enhances transverse resistivity and makes electromagnetic decoupling among filaments in AC fields. 3:00 PM R4-S3.5 Magnetic semiconductors have recently gained importance due to the demands for highly spin-polarised material to be integrated in spintronics devices. The rare earth nitrides (RN) offer a number of interesting properties in this regard; most members of the series are known to be ferromagnetic and band structure calculations have predicted both ferromagnetic semiconductors and half metals among them. A strong debate about the ground state is however not closed because the properties depend critically on the stoichiometry, which is not easily controlled, with both N vacancies and O impurities being common defects in early experiments. However a number of groups have recently grown well-characterised films in a vacuum environment, and developed passivating layers that permit ex situ measurements. Here we report magnetic measurements on nanocrystalline RN (R= Sm, Gd, Dy, Er) thin films prepared by thermal evaporation in ultra-high vacuum chamber with a low-pressure nitrogen gas atmosphere [1]. Rutherford backscattering spectroscopy (RBS) data establish that the films are highly stoichiometric and conductivity studies establish them as semiconductors. All order ferromagnetically below Curie temperatures of 69K, 25K, 30K and 6K, respectively for GdN, DyN, SmN and ErN. The saturation moment per rare earth atom measured in an applied field of 6T is 6.4, 5.5, 0.08 and 5 Bohr Magneton respectively.
The remarkably small moment in SmN results from a near cancellation of the spin and orbital contributions to the Sm3+ 4f magnetic moment. As a consequence, in the entire ferromagnetic temperature range a very stable single domain state is favoured at remanence when the film is thermally magnetised under a high magnetic field. Its weak coupling to an applied field dictates that it exhibits an enormous coercivity, similar to a ferrimagnet at the compensation point. Thus at 2K the magnetic field necessary to reverse the magnetisation is higher than the maximum available magnetic field of 6T. This suggests that SmN is a zero magnetisation ferromagnet similar to metallic Sm1-xGdxAl2, which shows a divergent coercivity at a well-defined temperature where the spin and orbital moments cancel [2]. Such zero-moment ferromagnetic materials offer the opportunity to act as sources of spin-polarised current without a perturbing stray field.
[1] S. Granville et al, Phys. Rev. B73, 235335 (2006)
[2] H. Adachi and H. Ino, Nature 401, 148 (1999) 3:15 PM R4-S3.6 Chromium dioxide is a half metal that has only one electron spin component at the Fermi level and therefore exhibits a very high degree of spin polarization making it a prime candidate for use in magnetoelectronic or so-called spintronic devices [1]. Interestingly CrO2 has been found to sustain a superconducting spin triplet state in a thin film in contact with superonducting electrodes [2] opening the way for novel devices such as magnetically switchable Josephson junctions and for studying the interplay between magnetism and superconductivity. A high pressure x-ray absorption spectroscopy study is presented of the electronic and magnetic properties of CrO2. Chromium K-edge x-ray magnetic circular dichroism (XMCD) profiles from powder that was placed under pressure using a perforated diamond anvil cell (DAC) were measured at beamline 4-ID-D at Advanced Photon Source in Chicago. The results indicate that magnetisation decreases linearly to close to a third of the ambient pressure value by 10GPa and then remains constant up to the highest measured pressure of 16GPa. This dependence is shown to be inconsistent with existing DFT calculations and also with the occurrence of a high to low spin transition that was suggested by other authors to accompany the structural phase transition at 12±3GPa. The antiferromagnetic superexchange coupling between the localised spins is expected to strengthen significantly as the Cr-O bond length shortens hence the possibility that the appearance of an antiferromagnetic phase at high pressure drives the observed magnetisation decrease is argued.
Ferromagnetism in CrO2 has been postulated to be stabilized by a double exchange mechanism which is dependent on a slight tetragonal distortion of the CrO6 octahedra causing localization of the dxy orbital while the dzx and dyz states remain itinerant [3]. Compression of the CrO2 lattice increases this octahedral distortion leading to an eventual structural phase change at 12±3GPa as well as introducing many other effects including band broadening, increased crystal field splitting and changes to the exchange coupling constants that are expected to have significant effect magnetic properties. Given that thin films are often grown on mismatched substrates leading to significant strain in the interface region the response of the magnetism and half-metallicity to changes in cell volume is extremely relevant to the manufacture of spintronic devices. Furthermore, the superconducting spin triplet current observed in CrO2 has its origins in processes occurring at the superconducting/half-metallic interface that are thought to be highly dependent on the nature of the local magnetic field present in the interfacial region [2,4] and therefore the details of how volume changes effect the magnetic degrees of freedom may also be crucial to an understanding of superconductivity in CrO2.
[1] R. J. Soulen Jr et. al., Science 282, 85 (1998)
[2] R. S. Keizer et. al., Nature 439, 04499 (2006)
[3] M.A. Korotin, V.I. Anisimov, D.I. Komskii, and G.A. Sawatzky, Phys. Rev. Lett. 80, 4305 (1998)
[4] J. Linder and A. Sudbo, Phys. Rev. B. 76, 214508 (2007) AFTERNOON BREAK 3:30 PM - 4:00 PM 4:00 PM R4-S4.1 Extensive investigation is continuing on soft magnetic materials for their uses mainly in microwave devices. Yttrium iron garnet (YIG) is one of the most suitable soft magnetic materials with extensive uses at microwave frequencies as isolators, circulators, etc.. Magnetic materials in general in their nanocrystalline state have attracted considerable attention in recent years . Microwave-Hydrothermal (MH) method is a novel technique, which involves atomic scale mixing, resulting in the increase of reaction rate and there by saves time and energy. Various types of nanocrystalline materials can be synthesised by this method at a comparatively lower temperature and less time than conventional method.
The coercivity of the magnetic materials has been found to depend markedly on the size of the crystallites. Controlling the particle size of magnetic materials in the nanometer range is therefore an effective means of altering the coercivity drastically to suit possible new applications for the material concerned. With this background, we have tried to synthesize for the first time YIG in nanocrystalline form using the Microwave-Hydrothermal method. The influence of pH value of the precursor solution and the garnet phase formation of synthesized powders were investigated by transmission electron microscopy (TEM), thermal analysis (DTA/TGA), infrared (IR) spectroscopy and X-ray diffraction technique (XRD). The results show that with increasing pH value, the phase formation increases slightly. The crystallite size of the single phase YIG prepared at pH~9 was 18 nm. In general, increasing the calcination temperature from 800 C/30 min. to 900 C/30 min. has resulted in increase of the crystallite size of YIG from 18 nm to 40 nm . The calcined powders showed porous feature due to the liberation of large amount of gases during the calcination. The coercivity of present nanocrystalline YIG changes from 40 to 100 Oe while the particle size varies from 18 to 24.5 nm. The Increase of effctive anisotrophy constant is attributed to the higher coercive force. Smaller saturation magnetization is caused by the fact that the volume fraction of nanocrystalline YIG in these material is rather small. 4:15 PM R4-S4.2 Cold Spray is an emerging technology for the deposition of materials without significant input of heat. This paper discusses the application of cold spray to several heat-sensitive materials. Low resistivity, adherent metallic coatings were deposited on polarised lead zirconate titanate (PZT) substrates, without affecting their polarisation state. The process offers a quick, low cost way of electroding piezoelectric elements. Rare earth magnetic Nd2Fe14B / Al composites and magnetostrictive Terfenol-D / Al composites have been produced by cold spray. Coatings and near-net shape components may be manufactured in this way. The magnetic properties before and after spray were assessed by vibrating sample magnetometry (VSM). 4:30 PM R4-S4.3 Ceramic materials that exhibit simultaneous ferroelectric and ferromagnetic properties have recently attracted much attention not only from the viewpoint of solid state physics but also because of their potential application in practical electronic devices such as electromagnetic interference (EMI) filters as well as chip inductor and capacitor integrated passive devices. Such materials are also called multiferroic materials. Materials that exhibit simultaneous ferroelectric and ferromagnetic properties are expected to produce new properties, such as magneto-electric, magneto-optic and other new coupling properties. However, very few such materials (with ferroelectric and ferromagnetic properties in one phase) exist in nature or have been synthesized in the laboratory.
In this study, a series of ferroelectric ferromagnetic composite materials that consist of the ferroelectric phase SrBi2Ta2O9 (SBT) and the ferromagnetic Ni0.2Cu0.2Zn0.6Fe2O4 (NiCuZn ferrite) phase, have been prepared using standard ceramic method. With the variation of x (x=SBT/(SBT+NiCuZn, weight percent), typical magnetic hysteresis loops of prepared composites have been observed. The coercivity increases with the increase of x, which indicates the magnetization ability becomes weak because of simultaneous presence of nonmagnetic SBT phase. The saturation magnetization of the composites linearly decreases with the increases of SBT content. On increasing the value of x, the initial permeability of the composites decreases and excellent frequency stability is exhibited. With the increase of the content of SBT, the peak of the quality factor for prepared composite materials tends to shift toward higher frequency. The Curie temperature of composite materials shifts toward higher temperature with the increase of x. The microstructures of the sintered composite materials also have been studied. 4:45 PM R4-S4.4 Lead-based materials, such as lead zirconate titanate (PZT) are the most important piezoelectrics and have been widely used for sensors and actuators. But in view of the environmental point, the lead-based piezoelectric materials contain hazardous lead oxides which have been gradually restricted. Therefore recently lead-free piezoelectric materials have been receiving increasing attentions. Sodium potassium niobate [(Na0.5K0.5)NbO3, KNN] has been expected as a promising candidate for a lead-free piezoelectric system.
In this talk, investigation on the preparation and properties of (Na0.5K0.5)NbO3 thin films have been presented. The KNN thin films have been successfully prepared by a sol-gel process and a pulsed laser deposition (PLD) process. In the sol-gel process, the precursor solutions were prepared from commercial sodium acetate, potassium acetate and niobium ethoxide synthesized in our laboratory. The KNN thin films were spin-coated on Pt coated Si wafers and followed by a rapid thermal treatment. In the PLD process, the KNN ceramic targets were prepared by a conventional ceramic process. A KrF excimer laser was used to deposit KNN thin films at a repetition frequency of 5 Hz and an energy density between 150~250 mJ/ pulse. The XRD analysis showed that sol-gel thin films annealed above 500 C were single phase with a perovskite structure. The surface of the thin films is compact and crack-free. The dielectric constant and loss tangent of the KNN thin films annealed at 650 C are 260 and 0.05 at 1 kHz, respectively. The crystal structure, dielectric, ferroelectric and piezoelectric properties of the KNN thin films prepared by both processes will be presented and discussed in details. 5:00 PM R4-S4.5 Aluminum nitride (AlN) is an extremely attractive material using as heat sinks and packages for microelectronic application for its remarkable properties, including high thermal conductivity, high electrical resistivity, a low dielectric constant and a low dielectric loss, as well as a low thermal expansion coefficient close to that of silicon. In this paper, a new precursor of alumina and carbon (Al2O3+C) was prepared using a low temperature combustion synthesis process with aluminum nitrate, urea and glucose as starting materials. AlN powder was synthesized by calcining this combustion synthesis precursor at 1500? for 2h under a flowing nitrogen gas. The particles of the synthesized AlN powder were about 100 nm in size. The specific surface area of the AlN powder was 17.4 m2/g. This kind of nanometer AlN powder had a high sinterability. AlN specimen doped with 5%Y2O3 could be well densified at 1650? for 4h by pressureless sintering. The thermal conductivity of the obtained AlN ceramic was 132.4 Wom-1oK-1.
Key words: AlN; Nanometer powder; Preparation; Sintering; Thermal conductivity 5:15 PM R4-S4.6 This works reports, for the first time, the thorough study and optimisation of Phase Change Memory (PCM) structure with thin metal inserted chalcogenide via thermal conductivity (?) and electrical resistivity (?) using finite element modeling. PCM is one of the best candidates for next generation non-volatile memory. It has received much attention recently due to its fast write speed, non-destructive readout, superb scalability, and great compatibility with current silicon-base mass fabrication. The setback of PCM is a high reset current typically higher than 1mA based on 180nm lithography. To reduce a reset current and to solve the over-programming fail, PCM with thin metal inserted chalcogenide (bottom chalcogenide/metal inserted/top chalcogenide) structure has been proposed. Nevertheless, reports on optimisation of both thermal conductivity and electrical resistivity using finite element method of this new PCM structure have never been published. This work aims to minimize a reset current of this PCM structure by optimizing the level of the thermal conductivity and electrical resistivity of the PCM profile using finite element approach. This work clearly shows that PCM characteristics are strongly affected by both parameters, the thermal conductivity and electrical resistivity. The 2-D simulation results obviously reveal that the best thermal transfer of and self-joule-heating at the bottom chalcogenide layer can be achieved under both conditions; (i) ?bottom chalcogenide>=?metal insert>?top chalcogenide and (ii) ?bottom chalcogenide>?top chalcogenide >=?metal insert. In conclusion, high energy efficiency can be obtained with the reset current below 0.3mA and with high speed operation of less than 30ns.
Room Temperature Ferromagnetic GaCrN Thin Film Growth by Hybrid Physical-Chemical Vapor Deposition. (#317) Chul Hwan Choi, Seon Hyo Kim, Hyo Jin Kim, Yuen Hee Jung;
Pohang University of Science and Technology, Republic of Korea.
The Growth Mechanism of Highly Ordered Ni Nanowires with Preferred Crystallographic Orientations. (#1133) Lumei Gao, Xiaoping Song, Sen Yang, Pangpang Wang, Liqun Wang;
School of Science, Xi'an Jiaotong University, Xi'an Shanxi, China.
Magnetic Nanopatterns Fabricated from Direct Writing Water Developable La0.7Sr0.3MnO3 Electron Beam Resist. (#502) Ming-Chung Wu, Yu-Ching Huang, Yi-Jen Wu, Chih-Min Chuang, Yang-Fang Chen, Wei-Fang Su;
National Taiwan University, Taipei, Taiwan.
Magnetic Enhancement of Nanocrystalline MnZn Ferrites by a Phase Transformation Method under a High Magnetic Field. (#1072) Yongsheng Liu,
Department of Mathematics and Physics, Shanghai University of Electric Power, Shanghai, China.
FePtRh Based Thin Films as Magnetic Underlayers for Perpendicular Recording Media. (#1060) Dieter Lott,
GKSS Research Center, Geesthacht, Germany.
Study on Bonded Rare Earth Giant Magnetostrictive Materials. (#904) Zhang Shengen,
School of Materials Science and Engineering, University of Science and Technology Beijing, China.
Epitaxy of Fe3Si Layers across FeSi2 Layers in Fe3Si/FeSi2 Superlattices. (#1050) Kaoru Takeda1, Tsuyoshi Yoshitake1, Yoshiki Sakamoto1, Tetsuya Ogawa1, Daisuke Hara1, Masaru Itakura1, Noriyuki Kuwano1, Toshinori Kajiwara2, Kunihito Nagayama3;
1Department of Applied Science for Electronics and Materials, Kyushu University, Fukuoka, Japan
; 2Department of Electrical Engineering, Fukuoka Institute of Technology, Japan
; 3Department of Aeronautics and Astronautics, Kyushu University, Japan.
Structural and Properties of Rare Earth Doped Bismuth Titanate Produced Using Wet Chemical Technique. (#135) Khairunisak Abdul Razak,
School of Material & Mineral Resources Engineering, Engineering Campus, Universiti Sains Malaysia, Penang, Malaysia.
The Effects of Oxygen Partial Pressure and Flux Content on Multiferroic BiFeO3 Thin Films Growth via Flux-Mediated Epitaxy. (#996) Ching-Jung Cheng,
The University of New South Wales, Sydney, Australia.
Gas Sensing Properties of MoO3 Film Fabricated Using Chemical Vapor Transport of MoO3(OH)2. (#970) Dae-Gun Kim, Young Jung Lee, Se Hoon Kim, Young Do Kim;
Department of Materials Science and Engineering, Hanyang University, Republic of Korea.
Single NV Centres in Diamond Created by Ion Implantation: Towards Optimised Production. (#837) Julius Orwa, Alberto Cimmino, Brant Gibson, David Simpson, Steven Prawer;
School of Physics, The University of Melbourne, Parkville, Victoria, Australia.
The Effect of Doping Aluminium on Thermal and Barrier Properties of Ta-N Thin-Films. (#1017) Jicheng Zhou1, Youzhen Li2;
1School of Electronics and Information Engineering, Central South University of Forestry and Technology, China
; 2School of Physical Science and Technology Central South University, China.
Growth and Physical Properties of MgB2 Films Deposited by Ultrasonic Spray Pyrolysis. (#1056) Jun-Ki Chung, Won-Jeong Kim, Sung Chang Park, Young Jin Lim, Cheol Jin Kim;
i-Cube Center and Advanced Material Research Center, Division of Nano & Advanced Materials Science and Engineering, Gyeongsang National University, Jinju, Republic of Korea.
The Thermodynamical, Transport and Magnetotransport Properties of Mn-Doped GaAs/InGaAs/GaAs Quantum Well with Ferromagnetism. (#1445) Ljudmila Shchurova, Vladimir Kulbachinskii;
Department of Solid State Physics, Physical Institute of RAS, Moscow, Russian Federation.
Study of Pb and Sb with Electrical Resistivity Measurement of Bi1.5-Pbx-Sby-Sr2-Ca2-Cu3O? Superconducting Systems, with X= 0.2 and Y= 0.3 Respectively. (#1449) Mumatz Humayun,
Department of EE, Mohammad Ali Jinnah University, Islamabad, Pakistan.
Fabrication and Electrical Properties of Au/PVDF-TrFe/LaZrOx/Si(100) Structure. (#988) Byung-Eun Park, Hui-Seong Han, Gwang-Geun Lee, Joo-Nam Kim, Hyung-Jin Park, Ho-Seung Jeon;
University of Seoul, Republic of Korea.
Ferroelectric-Gate Filed Effect Transistors Using Poly(vinylidene fluoride-trifluoroethylene) Copolymer Thin Films for Non-Volatile Memories. (#1019) Byung-Eun Park, Gwang-Geun Lee, Joo-Nam Kim, Hui-Seong Han, Hyung-Jin Park, Ho-Seung Jeon;
University of Seoul, Republic of Korea.
Developing the Multilayer Coated Conductors Wires on the Base of YBaCuO Superconductor Thin Films. (#1371) Serhiy Pysarenko, Alexey Pan, Shixue Dou;
Institute for Superconducting and Electronic Materials, The University of Wollongong, New South Wales, Australia.
Bismuth Pyrochlore Based Composite Thin Films for Tunable Applications. (#70) Wei Ren, Peng Shi, Xin Yan, Xiaoqing Wu, Xiaofeng Chen;
Electronic Materials Research Laboratory, Xi'an Jiaotong University, China.
* Please note: parallel R session (RR) at Level 2, Room 2
Chair: J. Tang
Tuesday, July 29, 2008
Level 2 - State Room, Hilton Sydney
Exploration of New Magnetoelectric Multiferroics. (#416) Tsuyoshi Kimura,
Osaka University, Japan.
Transition Metal Oxides Doped Well below the Percolation Threshold: Is Their Ferromagnetism Defect-Mediated?. (#450) Kannan M Krishnan1, Kelli Griffi-Roberts1, Maria Varela2, Sokrates Pantelides3, Steve J Pennycook2;
1Department of Materials Science, University of Washington, Seattle, USA
; 2Oak Ridge National Lab, Tennessee, USA
; 3Vanderbilt University, Nashville, Tennessee, USA.
Multiferroic Behavior of BiFeO3-Based Bilayer Structures. (#304) John Wang, Rongyan Zheng, Xingsen Gao, Seeram Ramakrishna;
Department of Materials Science and Engineering, Faculty of Engineering, National University of Singapore, Singapore.
Oxygen Vacancies Control of Crystal Structure and Magnetic Properties of (Tb1-xNax)MnO3-y. (#82) Ru-Shi Liu,
Department of Chemistry, National Taiwan University, Taipei, Taiwan.
Laser Damage and Domain Switching Studies in Near-Stoichiometric Nd-Zn-LiNbO3 Crystals. (#887) Babu Reddy J N, Ganesh Kamath K, Bhat H L, Suja Elizabeth;
Department of Physics, Indian Institute of Science, Bangalore, India.
* Please note: parallel R session (RR) at Level 2, Room 2
Chair: T. Kimura
Tuesday, July 29, 2008
Level 2 - State Room, Hilton Sydney
Theoretical Prediction on Half Metallic Antiferromagnet in Strongly Correlated Systems. (#241) Xiao Hu,
National Institute for Materials Science, Sengen, Tsukuba, Ibaraki, Japan.
Half-Metallicity of Fe3O4 and Amplification of Its Magnetoresistance in a MOSFET Structure. (#296) Jinke Tang1, Wendong Wang1, Ulrike Diebold2, Matthias Batzill3, Xianjie Wang4, Yu Sui4;
1Department of Physics & Astronomy, University of Wyoming, Laramie, USA
; 2Tulane University, New Orleans, Louisiana, USA
; 3University of South Florida, Tampa, USA
; 4Harbin Institute of Technology, Heilongjiang, China.
Nanomagnetism, Spintronics and Polarized Neutrons. (#370) Frank Richard Klose,
Bragg Institute, Australian Nuclear Science and Technology Organisation, Australia.
Epitaxial Growth of Cr2O3 Magnetoelectric Sputtered Films on Sapphire. (#405) Hiroshi Yamamoto, Nobuyuki Iwata, Takeshi Asada, Shummpei Otsuki;
Nihon University, Funabashi-shi, Chiba, Japan.
Layered Cobaltites: Synthesis, Crystal Growth, Transport and Magnetic Properties. (#542) Kazimierz Conder1, Marian Stingaciu1, Ekaterina Pomjakushina1, Andrei Podlesnyak2;
1Paul Scherrer Institute, Switzerland
; 2Hahn-Meitner-Institute, Switzerland.
Chair: X. Hu
Tuesday, July 29, 2008
Level 2 - State Room, Hilton Sydney
Mn Distribution in GeMn Thin Films Grown on Ge and Si Substrates. (#496) Yong Wang,
The University of Queensland, Brisbane, Australia.
Growth Mode of Graphene Layers Deposited on SiO2 Substrate. (#36) Zhi Min Ao1, Tao Liu1, Qing Jiang1, Sean Li2;
1Department of Materials Science & Engineering, Jilin University, Changchun, China
; 2The University of New South Wales, Australia.
Structural and Magnetic Field Dependent Transport Properties of MnxGe(1-x) Dilute Magnetic Semiconductor Thin Films Grown by Laser Ablation Technique. (#539) Sandip Majumdar, Amal Kumar Das, Samit Kumar Ray;
Department of Physics and Meteorology, Indian Institute of Technology, Kharagpur, India.
Effects of Varying Gd Concentration on Magnetic Properties of Zn1-xGdxO. (#356) Sze Ter Lim, Wen Dong Song, Kie Leong Teo, Thomas Liew, Tow Chong Chong;
Data Storage Institute, Agency for Science, Technology and Research, Singapore.
Growth and Electron Bands in the Intrinsic Ferromagnetic Semiconductor GdN. (#810) Andrew Preston1, Ben Ruck1, Jianping Zhong1, Mathias Kuebel1, Claire Meyer1, Joe Trodahl1, Kevin Smith2, Walter Lambrecht3, Nick Strickland4, Grant Williams4, Steven Durbin5, Ian Farrell5, James Downes6;
1MacDiarmid Institute, School of Chemical and Physical Sciences, Victoria University of Wellington, New Zealand
; 2Boston University, USA
; 3Case-Western Reserve University, USA
; 4Industrial Research Ltd., New Zealand
; 5University of Canterbury, Christchurch, New Zealand
; 6Macquarie University, Sydney, New South Wales, Australia.
Giant Magnetoimpedance Behaviour of FeCuCrVSivB Films and Multilayer Films Deposited in Magnetic Field. (#121) Wei Ping Chen1, Shang Shen Feng1, Jian Bo Wu1, Pei Yang Cai1, Shu Qin Xiao2, Yin Hua Liu2;
1Zhejiang Taizhou University, Zhejiang, China
; 2Shandong University, Jinan, China.
Chair: Rob Elliman, Laurie Faraone, C. Jagadish, Max Lu, John O'Connor
Tuesday, July 29, 2008
Level 3 - Grand Ballroom, Hilton Sydney
Characterization of YBCO Films' Epitaxial Growth Process by In-Depth Raman Profiling Spectra. (#1178) Maria Branescu, Coralie Naudin, Ian Ward;
National Institute for Materials Physics, Bucharest-Magurele, Romania.
Influence of Mechanically Milled and Glycerin Added Boron Powders on the Superconducting Properties of MgB2. (#369) Byung-Hyuk Jun, Yi-Jeong Kim, Kai Sin Tan, Nam-Kyu Kim, Chan-Joong Kim;
Korea Atomic Energy Research Institute, Republic of Korea.
Comprehensive study of carbohydrate doping on the superconductivity of MgB2/Fe wire
. (#936) Jung Ho Kim1, Jihyun Lee2, Xun Xu1, Haewoong Park2, Shixue Dou1;
1Institute for Superconducting and Electronic Materials, The University of Wollongong, New South Wales, Australia
; 2Korea University of Technology and Education, Republic of Korea.
Tc Enhancement for Nano-SiC Doped MgB2 Superconductors Sintered in Pulsed Magnetic Field. (#355) Wenxian Li,
Institute for Superconducting and Electronic Materials, The University of Wollongong, New South Wales, Australia.
Nonlinear Susceptibility Behaviour of Superconducting Ferromagnet: RuSr2Eu1.5Ce0.5Cu2O10. (#1232) R. Nigam, A. V. Pan, Shixue Dou;
Institute for Superconducting and Electronic Materials, The University of Wollongong, New South Wales, Australia.
Improved Critical Current Properties of the Undoped and Carbon Doped MgB2 Bulks Prepared by High Energy Ball Milling Process. (#975) Jihyun Lee, Haewoong Park, Chanjoong Kim;
Korea University of Technology and Education, Republic of Korea.
MoRe-Based and NbN-Based Tunnel Junctions and Their Characteristics. (#1193) Vladimir Evgenievych Shaternik1, Sergei Yurievych Larkin2, Mikhail Alexandrovych Belogolovskii3;
1G.V.Kurdyumov Institute for Metal Physics, Kiev, Ukraine
; 2Concern 'Nauka', Ukraine
; 3Donetsk Institute for Physics and Engineering, Ukraine.
The Critical Current Density in MgB2-xCx Superconductors. (#849) O. V. Shcherbakova, A. V. Pan, J. L. Wang, A. V. Shcherbakov, S. X. Dou, D. Wexler;
Institute for Superconducting and Electronic Materials, The University of Wollongong, New South Wales, Australia.
Magnetic and Pinning Properties of Superconducting Y0.93Pr0.07Ba2Cu3O7-? Single Crystal. (#309) Jincang Zhang1, Zhengping Qin1, Gang Jin2, Miaoqin Chen1, Xin Yao3, Chuanbing Cai1;
1Department of Physics, Shanghai University, China
; 2Zhoukou Normal University, China
; 3Shanghai Jiao Tong University, China.
Effect of Carbon Doping on Hc2 and Hirr of MgB2 by Using Sucrose (C12H22O11) as Carbon Source. (#298) Yun Zhang,
Institute for Superconducting and Electronic Materials, The University of Wollongong, New South Wales, Australia.
Novel Fabrication of Hollow Polystyrene/Magnetite Microspheres and Their Magnetorheological Characterization. (#118) Hyoung Jin Choi,
Inha University, Incheon, Republic of Korea.
Spin-glass nature of Dy
(0.50) Sr
(0.50) MnO
3. (#1152) Harikrishnan S.1, Naveen Kumar C.M.1, Bhat H.L.1, Suja Elizabeth1, Sahana Roessler2, Ulrich K. Roessler3, Kathrin Doerr3, Steffen Wirth2;
1Department of Physics, Indian Institute of Science, Bangalore, India
; 2Max Planck Institute for Chemical Physics of Solids, Germany
; 3IFW, Germany.
Invention of Half-Metallic Materials in Cuprates by First-Principles Calculations. (#381) Yung-Mau Nie, Xiao Hu;
International Center for Materials Nanoarchitectonics (MANA), National Institute for Materials Science, Japan.
A Synchrotron Photoemission Study of Cu3Mn{100}. (#969) Nicholas Alexander Loh1, Kuan Y. Hsieh2, Dehong Yu1, Robert A. Robinson1, Peter Brigden3, John D. Riley3, Robert L. Stamps4, Jih-Young Yuh2, Tun-Wen Pi2, Anton P. J. Stampfl1;
1Bragg Institute, Australian Nuclear Science and Technology Organisation, Australia
; 2National Synchrotron Radiation Research Center (NSRRC), Taiwan
; 3LaTrobe University, Victoria, Australia
; 4The University of Western Australia, Australia.
Magnetotransport Studies of fz-Grown Multiferroic Gd1-xSrxMnO3 Single Crystals. (#910) Aditya Avinash Wagh, H L Bhat, P S Anil Kumar, Suja Elizabeth Saji;
Department of Physics, Indian Institute of Science, Bangalore, India.
Two Mn Diffusion Modes in Magnetic Tunnel Junctions. (#672) Yong Wang,
The University of Queensland, Brisbane, Australia.
High-Coercivity Rod-Shaped Biphasic Assemblies of FePt-PtTe2 through Hybrid Templating. (#371) Qingyu Yan,
School of Materials Science and Engineering, Nanyang Technological University, Singapore.
Complex Impedance Analysis of Vanadium Doped SrBi2?(Ta0.9V0.1)2O9. (#255) Puja Goel1, Vijay Narayan Ojha1, Kanhaiya Lal Yadav2;
1National Physical Laboratory Delhi, India
; 2Indian Institute of Technology Roorkee, India.
Ferroelastic Domains in Ferroelectric Heterostructures with an Active Ferroelastic Buffer Layer
. (#939) Reza Mohammad Mahjoub, Anbusathaiah Varatharajan, Nagarajan Valanoor;
School of Materials Science and Engineering, The University of New South Wales, Sydney, Australia.
Influence of Ca-Doping on Local Crystal Chemistry and Dielectric Properties of Bi1.67O0.75Nb1.5O7 (M= Mg2+ and Ni2+). (#1054) Binh Hai Nguyen, Yun Liu, Ray L Withers;
Research School of Chemistry, The Australian National University, Australian Capital Territory, Australia.
Fabrication and Electricity Properties of Metal Covered Elastomer Microspheres by Electroless Plating. (#402) Gao Da-Li, Zhan Mao-Sheng, Wang Kai;
School of Materials Science and Engineering, Beijing University of Aeronautics and Astronautics, HaiDian District, BeiJing, China.
Solid State Synthesis and Luminescent Properties of SiAlON:Re(Re = rare earths) Phosphor Materials. (#372) Jeong Ho Ryu, Youn-Gon Park, Hyung Sik Won, Sang Hyeon Kim, Hideo Suzuki, Chulsoo Yoon;
SAMSUNG Electro-Mechanics Co., Ltd., Republic of Korea.
The Influence of Load and Thickness During Constrained Sintering of Al2O3/LTCC/Al2O3 Structure. (#1104) Dong-Hun Yeo, Jung-Hwan Cho, Hyo-Soon Shin, Youn-Woo Hong, Jong-Hee Kim, Sahn Nahm;
Division of Fusion and Convergence Technology, Korea Institute of Ceramic Engineering and Technology, Republic of Korea.
Preparation and Properties of SiCN Thin Film Diffusion Barrier for Cu Interconnect in ULSI. (#953) Jicheng Zhou1, Zhijie Shi2;
1School of Electronics and Information Engineering, Central South University of Forestry and Technology, China
; 2School of Physical Science and Technology Central South University, China.
Comparison of LTCC Sheet Properties with Different Milling Methods. (#1112) Hyo-Soon Shin, Hyeok-Jung Kwon, Dong-Hun Yeo, Youn-Woo Hong, Jong-Hee Kim, Yong-Soo Cho;
Division of Fusion and Convergence Technology, Korea Institute of Ceramic Engineering and Technology, Republic of Korea.
Thickness and Light Exposure Effect on Ferroelectric Properties of Ultrathin PbTiO3 Films. (#1450) Arturas Vailionis, Rene Meyer, Paul McIntyre;
Stanford University, California, USA.
Magnetic Phase Transition and Magnetic Entropy Change in Melt-Spun LaFe11.6Si1.4Bx (x=0-0.7) Ribbons. (#78) Kun Xie,
Shandong University of Science and Technology, China.
Studies on the Adhesion Property of Copper Paste on Ceramic Radiator Fins. (#1438) Xiaoyun Zhu, Jinming Long, Xianwang Yang;
Kunming University of Science and Technology, China.
Chair: Y. Liu
Wednesday, July 30, 2008
Level 2 - State Room, Hilton Sydney
Advanced Recording Heads towards 1Tb/In2. (#1259) Sining Mao,
Device Design and Technology, Western Digital, Fremont, California, USA.
Domain Walls - Information Carriers or Noise Sources in Nanomagnetic Systems?. (#336) John Chapman,
Department of Physics and Astronomy, University of Glasgow, United Kingdom.
Patterned Ferromagnetic Nanostructured Arrays. (#1231) Adekunle Olusola Adeyeye,
Department of Electrical and Computer Engineering, National University of Singapore, Singapore.
Ferromagnetic Transition Involves a Simultaneous Structural Change. (#721) Xiaobing Ren, Sen Yang;
Ferroic Physics Group, National Institute for Materials Science, Japan.
Targeted Hyperthermia Therapy for Liver Cancer Using Magnetic Microspheres. (#1275) S. Jones1, K. S. Rutherford1, S. S. Rozeleur1, Y. Wang2, N. S. Jain2, B. S. Hawkett2;
1Sirtex Medical Limited, Australia
; 2The University of Sydney, New South Wales, Australia.
Cobalt Oxides as Functional Materials: Thermoelectricity, Dielectrics, and Spintronics. (#1260) Ichiro Terasaki,
Department of Applied Physics, Waseda University, Shinjuku, Tokyo, Japan.
Chair: W. Wen
Wednesday, July 30, 2008
Level 2 - State Room, Hilton Sydney
Realization of Pure CoO2 and Prospect for the Phase Relations in the LixCoO2 System. (#1306) Hisao Yamauchi1, Teruki Motohashi1, Ryoji Kanno1, Guoqing Zheng2, Maarit Karppinen3;
1Materials and Structures Laboratory, Tokyo Institute of Technology, Yokohama, Japan
; 2Department of Physics, Okayama University, Japan
; 3Laboratory of Inorganic Chemistry, Helsinki University of Technology, Finland.
Magnetic Anisotropy and Easy Axes Distribution of Polycrystalline and Nanostructured Systems Obtained by Transverse Susceptibility Measurements. (#164) Javier F. Calleja, Rafael Matarranz, Jose Antonio Corrales, Borja Presa, M. Carmen Contreras;
Departamento de Física, Facultad de Ciencias, Universidad de Oviedo, Spain.
Effect of Radio Frequency Identification Set on Recording Head in Writing Process: At 125 KHz Low Frequency. (#512) Aphaiphak Pratoomthip, Assoc. Prof. Dr.Apirat Siritaratiwat;
Khon Kaen University, Thailand.
Possible Quantum Orbital Transfer in Phase-Separated Manganites. (#874) Guixin Cao, Jincang Zhang, Shixun Cao, Chao Jing, Xuechu Shen;
Department of Physics, Shanghai University, China.
Magnetic Anistropy of Different Structured CrTe Thin Films Grown by Molecular Beam Epitaxy. (#66) Bi Jingfeng,
Information Storage Material Laboratory, Faculty of Engineering, National University of Singapore, Singapore.
Preparation and Electromagnetic Property of Low Density Core-Shell Co ⁄ Hollow Glass Microspheres Composite Powder. (#238) Liu Jian Hua, You Dun, Li Song Mei;
Beijing University of Aeronautics and Astronautics, HaiDian District, BeiJing, China.
Chair: F. Klose
Wednesday, July 30, 2008
Level 2 - State Room, Hilton Sydney
Study the Structure of Ru Doped FePt Nanoparticles. (#171) Chih-Hao Lee, Jen-Ho Hsu, Tzu-Wen Huang;
Department of Engineering and System Science, National Tsing Hua University, Hsinchu, Taiwan.
Temperature Dependent Magneto-Transport Studies in Ferromagnetic Ge1-xMnxTe. (#879) Cheow Hin Sim, Wen Qian Chen, Sze Ter Lim, Jing Feng Bi, Kie Leong Teo, Thomas Liew, Tow Chong Chong;
Data Storage Institute, Agency for Science, Technology and Research, Singapore.
Fe3Si/FeSi2 Superlattices Prepared at Elevated Temperatures. (#950) Kaoru Takeda1, Tsuyoshi Yoshitake1, Yoshiki Sakamoto1, Tetsuya Ogawa1, Daisuke Hara1, Masaru Itakura1, Noriyuki Kuwano1, Toshinori Kajiwara2, Kunihito Nagayama3;
1Department of Applied Science for Electronics and Materials, Kyushu University, Fukuoka, Japan
; 2Department of Electrical Engineering, Fukuoka Institute of Technology, Japan
; 3Department of Aeronautics and Astronautics, Kyushu University, Japan.
Atom Probe Tomography of Diluted Magnetic Semiconductors. (#559) Rongkun Zheng, Xuefeng Wang, Zongwen Liu, Simon P Ringer;
The University of Sydney, New South Wales, Australia.
Electrostatic Discharge Effect on TMR Recording Head: A Flex on Suspension Capacitance Approach. (#576) Nuttachai Jutong1, Apirat Siritaratiwat2;
1Khon Kaen University, Thailand
; 2I/UCRC, Thailand.
Serial Electrostatic Discharge Effects on GMR Recording Heads Using Wavelet Transform Technique Approach. (#367) Nattawoot - Suwannata, Apirat Siritaratiwat;
Department of Electrical Engineering, Khon Kaen University, Thailand.
Chair: J. Chapman
Thursday, July 31, 2008
Level 2 - State Room, Hilton Sydney
PDMS-Based Conducting Composite and Its Application in Micro-Electronic Fabrications. (#715) Weijia Wen,
Department of Physics, The Hong Kong University of Science and Technology, Hong Kong.
Novel Candidate for Multiferroics: A-Site Ordered Perovskite BiMn7O12-Δ. (#1307) Maarit Karppinen1, Naoki Imamura2, Teruki Motohashi2, Mitsuru Itoh2, Hisao Yamauchi2;
1Department of Chemistry, Helsinki University of Technology, Espoo, Finland
; 2Materials and Structures Laboratory, Tokyo Institute of Technology, Yokohama, Finland.
Combinatorial Discovery of a Morphotropic Phase Boundary in a Lead-Free High Tc Piezoelectric Perovskite. (#926) Shigehiro Fujino1, Anbusathaiah Varatharajan2, Ching-Jung Cheng2, Sung-Hwan Lim1, Makoto Murakami1, Paul Munroe2, Lourdes Salamanca-Riba1, Ichiro Takeuchi1, Nagarajan Valanoor2;
1University of Maryland, USA
; 2The University of New South Wales, Sydney, Australia.
Ordering/Disordering in Functional Relaxors. (#112) Yun Liu1, Ray L Withers2;
1Research School of Chemistry, The Australian National University, Australian Capital Territory, Australia
; 2The Australian National University, Australia.
Growth of K-Na-A (A: Rb, Cs) Niobate Single Crystals and Their Electric Properties. (#942) Hideo Kimura1, Rumi Tanahashi1, Koji Maiwa1, Haruo Baba1, Zhenxiang Cheng2, Xiaolin Wang2;
1Crystal Science and Technology Group, Innovative Materials Engineering Laboratories, National Institute for Materials Science, Sengen, Tsukuba, Ibaraki, Japan
; 2Institute for Superconducting and Electronic Materials, University of Wollongong, Australia.
Low Loss Dielectric Materials for High Frequency Applications. (#925) Mohan Jacob,
James Cook University, Brisbane, Queensland, Australia.
Chair: H. Habermeier
Thursday, July 31, 2008
Level 2 - State Room, Hilton Sydney
MgB2 Thin Films for High Field, Electronics and RF Applications. (#1305) Xiaoxing Xi,
Department of Physics and Materials Science and Engineering, The Pennsylvania State University, USA.
High pressure growth, structure refinement and superconducting properties of SmAsFeO1-xFy single crystals and polycrystalline samples.. (#406) Janusz Karpinski1, Nikolai D Zhigadlo1, Sergei Katrych1, Bertram Batlogg1, Krzysztof Rogacki2, Roman Puzniak3;
1Laboratory for Solid State Physics, Swiss Federal Institute of Technology, ETH Zürich, Switzerland
; 2Institute of Low Temperature and Structural Research Wroclaw, Poland
; 3Institute of Physics, Polish Academy Science, Warszaw, Poland.
Flux Pinning Properties by Artificial Nanorods in IBAD/PLD GdBCO Coated Conductors. (#630) Teruo Matsushita,
Departmernt of Computer Science and Electronics, Kyushu Institute of Technology, Fukuoka Prefecture, Japan.
Do-It-Yourself Flux Pinning Engineering in High Tc Superconductors. (#1246) Kaname Matsumoto,
Department of Materials Science and Engineering, Kyushu Institute of Technology, Fukuoka Prefecture, Japan.
Raman Investigations on Li, Mn, and C Doping of MgB2. (#875) Paraskevas Parisiades1, Efthymios Liarokapis1, Nicolai Zhigadlo2, Sergei Katrych2, Janusz Karpinski2;
1National Technical University of Athens, Greece
; 2ETH Zurich, Switzerland.
Josephson-Like Behaviour of Nanostructured Granular Carbon Films. (#23) Sergey G. Lebedev,
Department of Experimental Physics, Institute for Nuclear Research of Russian Academy of Sciences, Russian Federation.
Chair: X. Ren
Thursday, July 31, 2008
Level 2 - State Room, Hilton Sydney
CeO2|NiO|Ni Buffer Layer Formation for YBCO Coated Conductors. (#847) Zainovia Lockman,
School of Materials Engineering, Engineering Campus, Universiti Sains Malaysia, Penang, Malaysia.
Microstructural Modifications and Superconducting Property Control in Multilayered Thin Films. (#1227) Alexey V Pan, Serhiy Pysarenko, Shixue Dou;
The University of Wollongong, New South Wales, Australia.
Reel-to-Reel Continuous Deposition of CexZr1-xO2 Single Buffer Layer for YBCO Coated Conductors. (#626) Jie Xiong,
State Key Lab of Electronic Thin Films and Integrated Devices, University of Electronic Science and Technology of China, Chengdu, China.
Fabrication and Characterization of Bi2223 Tapes with Resistive Barriers for Reducing AC Losses. (#42) Akio Oota1, Ryoji Inada1, Yoshiki Mitsuno1, Kazuma Souguchi1, Yuichi Nakamura1, Chengshan Li2, Pingxiang Zhang2;
1Department of Electrical and Electronic Engineering, Toyohashi University of Technology, Japan
; 2Northwest Institute for Nonferrous Metal Research, China.
Ferromagnetism in Rare Earth Nitrides. (#811) Claire Meyer1, Andrew Preston1, Ben Ruck1, Joe Trodahl1, Jianping Zhong1, Simon Granville1, Grant Williams2;
1MacDiarmid Institute, School of Chemical and Physical Sciences, Victoria University of Wellington, New Zealand
; 2Industrial Research Ltd, New Zealand.
The Magnetism of CrO2 under High Pressure. (#779) NIcholas Alexander Loh1, Justin King-Lacroix2, Dehong Yu1, Robert Robinson1, Robert L. Stamps3, Yuan-Cheih Tseng4, Daniel Haskel4, Anton P. J. Stampfl1;
1Bragg Institute, Australian Nuclear Science and Technology Organisation, Australia
; 2The University of New South Wales, Sydney, Australia
; 3The University of Western Australia, Australia
; 4Argonne National Laboratory, USA.
Chair: X. L. Wang
Thursday, July 31, 2008
Level 2 - State Room, Hilton Sydney
Synthesis of Nanocrystalline Yttrium Iron Garnet. (#266) Sabaru Ramana Murthy, Sadana K;
Materials Science and Nanophysics, Department of Physics, Osmania University, Hyderabad, India.
Cold Spray of Piezoelectric, Magnetic and Magnetostrictive Materials. (#940) Peter C King, Saden H Zahiri, Mahnaz Jahedi;
Australian Commonwealth Scientific and Research Organization (CSIRO), Australia.
Magnetic Properties of Multiferroic Material. (#575) Xi Wei Qi,
Department of Materials Science and Engineering, Northeastern University at Qinhuangdao Branch, QinHuangDao, China.
Lead-Free (Na, K)NbO3 Piezoelectric Thin Films: Preparation, Structures and Electrical Properties. (#71) Wei Ren, Xiaoqing Wu, Lingyan Wang, Aifeng Tian, Xin Yan, Peng Shi, Xiaofeng Chen;
Electronic Materials Research Laboratory, Xi'an Jiaotong University, China.
Preparation and Sintering of Nanometer AlN Powder. (#718) Qin Mingli, Qu Xuanhui, Zhang Shengen, Wang Jian, Lou Tiegang;
Materials Science and Engineering School, University of Science and Technology of Beijing, China.
Optimisation of Phase Change Memory with Thin Metal Inserted Layer on Material Properties by Using Finite Element Modelling. (#864) Sanchai Harnsoongnoen1, Chiranut Sa-Ngiamsak2, Apirat Siritaratiwat1;
1I/U CRC in Hard Disk Drive Component, Thailand
; 2Department of Electrical Engineering, Faculty of Engineering, Khon Kaen University, Khon Kaen, Thailand.
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