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We have investigated the preparation, structures, and magnetic properties of bulk Fe2CrSi and Fe2Cr1-xTixSi Heusler alloys. Although a Cr-rich secondary phase coexists with the Heusler mother phase in stoichiometric Fe2CrSi samples, high temperature annealing (1200°C) effectively reduces the extent of the Cr-rich secondary phase. We found that pure single-phase samples can be prepared in a narrow composition range of 22% Cr. For a Fe2Cr1-xTixSi system with Ti content x of up to 1/8, virtually single-phase Heusler alloys have been obtained. The saturation magnetization of Fe2Cr1-xTixSi decreased with increasing Ti content, while their Curie temperatures Tc remained constant.

GMR multilayer films using Co2MnGe(CMG) and Mn-Ir/CMG exchange-coupled films were fabricated on thermally oxidized Si substrate, and their crystal orientation, magnetic properties, and interfacial roughness were investigated. The main results are stated as follows. (1) (100) oriented MnIr/CMG exchange-coupled films were realized when Ni-Ta underlayer/Cr buffer layer were deposited on thermally oxidized Si substrate. After thermal annealing for 2h at 250°C in a magnetic field of 5 kOe, the unidirectional anisotropy constant (JK) of bilayers was 0.13 erg/cm2. (2) Dependence of saturation field (Hs) on Cr thickness for GMR films with (100) oriented CMG/Cr/CMG trilayer was investigated. Hs was minimum when Cr thickness was 1 nm and 5 nm. (3) Surface roughness (Ra) of Ni-Ta 5 nm on Al-Cr bottom electrode layer(100 nm) was 0.108 nm. (4) Flat and (100) oriented CMG/Cr films was formed on Al-Cr bottom electrode layer (100 nm)/Ni-Ta underlayer (15 nm)/Cr buffer layer (60 nm) when Cr content of the Al-Cr layer was 18.7-24.6 at%.

Thin films of ordered double perovskite Sr2CrReO6 were sputter-deposited on SrTiO3 (001), (111), LaAlO3 (001) substrates. With high quality thin films of the double perovskite Sr2CrReO6, we have investigated the electronic state of the inside of the Sr2CrReO6 thin films by Synchrotron Radiation photoelectron spectroscopy (XPS). The Re 4f spectrum of Sr2CrReO6 has shown a multiple peak structure, which originates from the electronic state of Re in half-metallic Sr2CrReO6. Moreover, it has been found that the electronic densities of states clearly exist on the Fermi energy.

Thin films of ordered double perovskite Sr2FeMoO6 were sputter-deposited on Ba0.4Sr0.6TiO3-buffered SrTiO3 substrates, and their surface properties were examined by atomic force microscopy (AFM) and X-ray photoemission spectroscopy (XPS). The Mo 3d spectra of Sr2FeMoO6 films showed a multiple peak structure, which originated from the unusual electronic state of metallic Sr2FeMoO6. Systematic XPS studies of the air-exposed surface of Sr2FeMoO6 film indicated that the surface native barrier was an insulating SrMoO4. In addition, a TMR junction with the native barrier was fabricated using a convention photolithographic technique, and an MR ratio of 10 % was observed at 4.2 K.

We report studies on Andreev reflection measurements of ferromagnetic materials at junction interfaces using AlN/NbN junctions. We found that the junction resistance R can be controlled by varying the thickness and growth temperature of an AlN interlayer. The spin polarization of Co was determined to be PCo ≈ 0.44 from theoretical fitting of the conductance data for these junctions. The behavior of PCo and the dimensionless barrier parameter Z depending on the junction resistance R is discussed.

The structural and magnetic properties of Co2MnSi thin film grown by the ion beam sputtering method were investigated. Films grown on glass substrate at temperatures from 300°C to 600°C were polycrystalline, as were films grown on Si(100) and MgO(100) substrates at 600°C. The crystalline quality of the film improved with increasing substrate temperature. Film grown at 600°C showed the largest magnetization near the bulk value. On the other hand, film with the preferred orientation to the (001) plane was obtained by growing a Ta buffer layer before the growth of Co2MnSi film on any substrates. The saturation magnetization increased with the increase of substrate temperature. This fact is considered to be due to the increase of the long-range order parameter.

Insulator layers of Nd2CuO4 (NCO) and Ba0.4Sr0.6TiO3 (BSTO), which have a good lattice matching to SFMO, were epitaxialy grown on SFMO by magnetron sputering in different preparation atmospheres (Ar, Ar+H2, Ar+O2). The quality of SFMO was evaluated by measurement of magnetization and crystal structure. We suggest that insulator materials having a small misfit to SFMO and the same preparation condition (Ar+H2) as SFMO are suitable as insulators of TMR junctions. We also demonstrated the hetero-epitaxial growth of SFMO/NCO/SFMO trilayers.

Spin polarization and electronic structure of Co90Fe10 were investigated through tunneling magnetoresistance (TMR) effect measurements on the Mn80Ir20/Ni80Fe20/Co90Fe10/SrTiO3/La0.7Sr0.3MnO3 junction. This junction was fabricated with half-metallic ferromagneto-LSMO and has a spin-valve type structure. An inverse TMR of 14 % was observed at 4.2 K. As the spin polarization of the LSMO is positive, the inverse TMR observed in this junction indicates a negative polarization for Co90Fe10 at the interface. The bias dependence of TMR is asymmetric to the applied bias. The band structure calculated with the LMTO-CPA method showed that spin polarization for Co90Fe10 is negative at the Fermi level.

The interface structure of Fe(Co)/AlOx/Fe ferromagnetic tunnel junctions (MTJ) was studied. Junctions were prepared by the metal mask method on glass, MgO(001), and sapphire (1120) substrates, using molecular beam epitaxy (MBE) and ion beam sputtering (IBS). The surface of a lower-electrode Fe layer grown on single-crystal MgO and sapphire by MBE was rougher than that deposited on a glass substrate by IBS. Al oxide barrier layers were prepared by natural oxidation of Al metal or direct deposition of Al2O3. AFM observation showed that the flattest surface of Al oxide was obtained by the direct deposition of Al2O3. CEMS measurement revealed that 65% of Fe atoms at interfaces between Fe and AlOX were oxidized or alloyed when the Al layer was oxidized at 50°C for 48 hours in air. On the other hand, in the case of Fe(Co)/Al metal/Fe and Fe(Co)/Al2O3/Fe, only two ferromagnetic components, pure Fe and Fe(Co), were observed, suggesting the existence of pin holes in the Al or Al2O3 layer.

The electrical and magnetic properties, including the magnetoresistance (MR) effect, of Lan-nxCa1+nxMnnO3n+1 thin films (n = ∞, 2; x = 0.3) grown on various substrates were investigated. For n = 2 (La1.4Ca1.6Mn2O7) thin films, the cusp temperature (Tcρ) in the ρ-T curve decreased very sharply with a decrease of the out-of-plane lattice parameter (a). The MR effect was enhanced drastically by decreasing Tcρ. These behaviors are interpreted in relation to the change in the transport character along the c-axis due to the strain.

Ferromagnetic moment, a magnetic critical exponent β and Curie temperature (TC) of γ-Fe/Cu multilayer (0.8 to 7.2 ML Fe thickness) prepared by the molecular beam epitaxy (MBE) method have been investigated. The crystal structure of γ-Fe layer is distorted tetragonally (c/a>1) for the Fe thickness less than 4.5 monolayer (ML) and cubic for thicker films. Magnetization (M) of γ-Fe is increased with decreasing Fe layer thickness because of the increase of the ratio of high spin state γ-Fe atoms to total Fe atoms at interfaces. A critical exponent in a relationship M/MS = (1-T/TC) β, is estimated to be 0.30±0.02. TC is decreased with decreasing Fe layer thickness. The behavior is explained by taking into account of the number of nearest neighbor Fe atoms around an Fe atom.

The lattice parameter, transport properties, and magnetoresistance effect of perovskite manganite La0.7Ca0.3MnO3thin films deposited on several substrates (SrTiO3(001), LaSrGaO4(001), YAlO3(001), LaA1O3 (001)) have been investigated in the range of themismatchof -4∼1% between the film and the substrates. We have found that metal-insulator transition temperature (Tcρ)depend on the out-of-plane lattice parameter (c). Magnetoresistance effect increases linearly with decreasing Tcρ. These results are understood in terms of the latticeeffect induced by the strain.