Komomo Kodama

Current-perpendicular-to-plane giant magnetoresistance of a spin valve using Co2MnSi Heusler alloy electrodes

We report the current-perpendicular-to-plane (CPP) giant magnetoresistance (GMR) 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.We report the current-perpendicular-to-plane (CPP) giant magnetoresistance (GMR) 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.

Structure and transport properties of current-perpendicular-to-plane spin valves using Co2FeAl0.5Si0.5 and Co2MnSi Heusler alloy electrodes

We report the structure and transport properties of current-perpendicular-to-plane spin valves (CPP SVs) with Co2FeAl0.5Si0.5 (CFAS) or Co2MnSi (CMS) Heusler alloy magnetic layers and an Ag or Cu spacer layer. A multilayer stack of sub/Cr/Ag/Heusler/(Ag or Cu)/ Heusler/Co75Fe25/Ir22Mn78/Ru was deposited on a MgO(001) single crystalline substrate by magnetron sputtering. Transmission electron microscopy observations showed epitaxial growth from the substrate to the top Heusler layer. The CPP SV with a CFAS/Ag/CFAS trilayer showed relatively large magnetoresistance (MR) ratios of 12% at room temperature and 31% at 12 K, with monotonous temperature dependence. However, the MR values of the SV with the CMS/Ag/CMS trilayer showed a different temperature dependence with a maximum value of 22% at 100 K. This might be related to the 90° couplings between the two CMS layers.

Impact of Ba to Si deposition rate ratios during molecular beam epitaxy on carrier concentration and spectral response of BaSi2 epitaxial films

Undoped 0.5-μm-thick BaSi2 epitaxial films were grown on Si(111) substrates with various ratios of the Ba deposition rate to the Si deposition rate (RBa/RSi) ranging from 1.0 to 5.1, and their electrical and optical properties were characterized. The photoresponse spectra drastically changed as a function of RBa/RSi, and the quantum efficiency reached a maximum at RBa/RSiu2009=u20092.2. Hall measurements and capacitance versus voltage measurements revealed that the electron concentration drastically decreased as RBa/RSi approached 2.2, and the BaSi2 films with RBa/RSi=u20092.0, 2.2, and 2.6 exhibited p-type conductivity. The lowest hole concentration of approximately 1u2009×u20091015u2009cm−3 was obtained for the BaSi2 grown with RBa/RSiu2009=u20092.2, which is the lowest value ever reported. First-principles calculations suggest that Si vacancies give rise to localized states within the bandgap of BaSi2 and therefore degrade the minority-carrier properties.

Interlayer exchange coupling in Co2FeAl0.5Si0.5/Cr/Co2FeAl0.5Si0.5 trilayers

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° 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.