Exploration of new spintronics materials by vapor phase epitaxy approach

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(1)Micro-structural analyses and Magnetic circular dichroism study of Co doped TiO_2 thin filmsThe 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 substrateAn ultra-smooth TiO_2 single crystal substrate was developed to exhibit a step and terrace structure. On the ultra-smooth substrate, the … More 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 filmsAt 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 filmsHighly 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 MaterialsA 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