2005 Fiscal Year Final Research Report Summary
Exploration of new spintronics materials by vapor phase epitaxy approach
| Project/Area Number |
14076212
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| Research Category |
Grant-in-Aid for Scientific Research on Priority Areas
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| Allocation Type | Single-year Grants |
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| Review Section |
Science and Engineering
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| Research Institution | Materials and Structures Laboratory |
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Principal Investigator |
MATSUMOTO Yuji Tokyo Institute of Technology Materials and Structures Laboratory, Associate Professor, 応用セラミックス研究所, 助教授 (60302981)
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| Project Period (FY) |
2002 – 2005
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| Keywords | Laser MBE / Co : TiO_2 / Magneto-optics / EXAFS, XANES / Combinatorial thin film preparatiorj / XMCD / magnetic superconductor. |
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| Research Abstract |
(1)Micro-structural analyses and Magnetic circular dichroism study of Co doped TiO_2 thin films
The local structure and electronic state of Co in anatase Co_xTi_<1-x>O_2 films were investigated by Co K-shell x-ray absorption near-edge structure (XANES) and extended x-ray absorption fine structure (EXAFS). There are often observed two kinds of Co in +2 formal oxidation state and metallic small clustering. A significant correlation between the observed ferromagnetism and the electronic band structure of TiO_2 host material was suggested by magnetic circular dichroism (MCD) study. Furthermore, synchrotron-radiation XMCD experiment for Co : TiO_2 anatase film concluded that the origin of the ferromagnetism was from Co^<2+> state but not from metallic Co.
(2)Low temperature growth of Co-doped rutile thin film on the ultra-smooth TiO_2 single crystal substrate
An ultra-smooth TiO_2 single crystal substrate was developed to exhibit a step and terrace structure. On the ultra-smooth substrate, the
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homo-epitaxial growth of TiO_2 was found to proceed even at 300℃, relatively much lower than that for the TiO_2 growth on a conventionally used stepped □-sapphire substrate. The low temperature growth enabled to grow a high-quality Co-doped TiO_2 film with no impurity phase. X-ray photoelectron spectroscopy and x-ray absorption fine structure revealed that the doped Co in the films took 'a valence state of 2+ and substituted for Ti site. However, the ferromagnetism was not detected down to 4K, owing to the highly insulating nature of the films.
(3)Carrier injection into highly insulating Co : TiO_2 films
At first, field-effect transistor (FET) was fabricated based on a Co : TiO_2 ruffle active channel. Top-gate transistor structure with amorphous. LaA103 insulator was fabricated on the Co : TiO_2 film grown on a.1102(110) ultra-smooth substrate. However, the high-leakage current property in the film prevented the appropriate performance of the TFT device. Next, during the alternate growth of insulating Co : TiO_2 and conductive TiO_2, an oxygen partial pressure PO_2 was modulated. The ferromagnetism in the artificial lattice was found to increase by decreasing the PO_2 for the growth of TiO_2. This enhancement of the ferromagnetism might be due to carrier injection from the conductive 1102 layer to the insulating Co : TiO_2 layer, as was evidenced by synchrotron-radiation XPS experiments of the Co : TiO_2/Nb : TiO_2 interface.
(4)Flux-assisted reactive solid phase epitaxy of highly c-axis oriented Ru(Eu1.5Ce0.5)Sr2Cu2O10_d thin films
Highly c-axis oriented epitaxial Ru(Eu1.5Ce0.5)Sr2Cu2O10_d (Ru-1222) thin lms were grown on SrTiO3 (001) substrates by a novel growth technique,ux-assisted reactive solid phase epitaxy. The lms grew epitaxially as (100)Ru-1222//(100)SrTiO3 with excellent crystallinity and atomically at terraces and steps. The magnetization dala are consistent with that reported for bulk Ru-1222 samples. The lms are suggested to be grantlar superconducting. Although zero resistance was not obtained at temperatures down to 5 K, the onset of superconducting transition was observed at about 25 K within the ferromagnetic order.
(5)Design of Combinatorial Shadow Masks for Complete Ternary-Phase Diagramming of Solid State Materials
A novel mask was designed for the combinatorial synthesis of a ternary composition spreads library, which allows such libraries to be deposited through a series of simple masks on a rotatable mount. This eliminates the use of complicated actuation of a heated substrate. In our configuration, this design leads to a standard linear phase diagram by varying the growth rate of each constituent nearly linearly from 0 to 100% at a triangular area on the substrate. Film growth occurs as a series of cycles in which one molecular layer of the material is deposited over the entire area of the spread by a synchronization of the mask movement, target exchange, and laser pulses: Less
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Research Products
(10 results)
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[Journal Article] X-ray Magnetic Circular Dichroism and StructureModel for Co-Doped Ti02(Anatase)Thin Film2004
Author(s)
N.Shimizu, S.Sasaki, T.Hanashima, K.Yamawaki, H.Udagawa, N.Kawamura, M.Suzuki, H.Maruyama, M.Murakami, Y.Matsumoto, H.Koinuma
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Journal Title
J. Phys. Soc. Jpn. 73
Pages: 800-803
Description
「研究成果報告書概要(欧文)」より
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