Search

We report the current-perpendicular-to-plane giant magnetoresistance of a spin valve with Co2MnSi (CMS) Heusler alloy ferromagnetic electrodes. A multilayer stack of Cr/Ag/Cr/CMS/Cu/CMS/Fe25Co75/Ir28Mn72/Ru was deposited on a MgO (001) single crystal substrate. The bottom CMS layer was epitaxially grown on the Cr/Ag/Cr buffer layers and was ordered to the L21 structure after annealing at 673 K. The upper CMS layer was found to grow epitaxially on the Cu spacer layer despite the large lattice mismatch between Cu and CMS. The highest MR ratios of 8.6% and 30.7% for CPP-GMR were recorded at room temperature and 6 K, respectively. The high spin polarization of the epitaxial CMS layers is the most likely origin of the high MR ratio., Comment: 14 pages, 3 figures, presented at the 53rd Annual Conference on Magnetism and Magnetic Materials, to be published in J. Appl. Phys

Interlayer exchange couplings were examined for Co2FeAl0.5Si0.5(CFAS)/Cr/CFAS trilayered films grown on MgO (001) single crystal and thermally oxidized Si substrates. The films were (001) epitaxial on MgO and (110) textured polycrystalline on SiO2. Strong exchange couplings were observed for the films with the 1.5 nm thick Cr spacer layer. A 90 degree coupling is dominant in the (001) epitaxial film. In contrast, an antiparallel coupling exists in the polycrystalline one. The relationship of interlayer couplings with the structure is discussed., Comment: 12 pages, 4 figures, presented at the 53rd Annual Conference on Magnetism and Magnetic Materials, to be published in J. Appl. Phys

The composition dependence of the Yb valence and of the thermal expansion have been studied in the YbGa$_x$Ge$_{2-x}$ system. X-ray diffraction reveals that single-phased samples isostructural to YbGaGe are obtained in the range of 0.9 <= x <= 1.5. The magnetic susceptibility shows that the systems are almost nonmagnetic below room temperature, indicating a stable Yb2+ state for the x range 0.9 <= x <= 1.5. The lattice constants as well as the lattice volume of these systems are found to decrease monotonically with decreasing temperature, suggesting the absence of zero thermal-expansion previously reported for YbGaGe., Comment: To appear in J. Alloys Compd

Crystal structure of spinel compound CuIr$_{2}$S$_{4}$ was examined by powder X-ray diffraction for the insulating phase below the metal-insulator transition at $T_{MI}$ = 230 K. The superstructure spots are reproduced by considering the displacement of Ir atoms. A model for the ionic ordering of Ir$^{4+}$ and Ir$^{3+}$ with the same number is proposed for the insulating phase on the basis of the structural analysis. The model suggests that the structural change at $T_{MI}$ is driven by the formation Ir$^{4+}$ dimers. In addition, we found that the superstructure spots becomes significantly weak below 60 K, without any significant effects on electric and magnetic properties. Possible mechanism for the transition is discussed., Comment: 10 pages, 4 figures, submitted to J. Phys. Soc. Japan