Search

Interlayer exchange couplings are examined for [Co.sub.2]Fe[Al.sub.0.5][Si.sub.0.5]/Cr/[Co.sub.2]Fe[Al.sub.0.5][Si.sub.0.5] trilayers films grown on MgO (001) single crystal and thermally oxidized Si substrates. Strong exchange couplings are observed for the films with the Cr spacer layer and the relationship of interlayer couplings with the structure is discussed.

The effect of Cr substitution for Fe on the spin polarization of [Co.sub.2][Cr.sub.x][Fe.sub.1-x]Si Heusler alloys is examined by using the point contact Andreev reflection method. The increase in spin polarization is attributed to both the improved [L2.sub.1] ordering as well as the half-metallicity obtained by ab initio calculations.

We investigated the structure and magneto-transport properties of magnetic tunnel junctions (MTJs) consisting of half-metallic Co2FeGa0.5Ge0.5 ferromagnetic electrodes and a semiconductive CuGaSe2 interlayer. The magnetoresistance (MR) ratio reaches more than 100% at room temperature and nearly 250% at 30 K with the resistance area product (RA) smaller than 1 Ω μm2. Microstructural analysis clarified that Co and Fe atoms diffuse into the CuGaSe2 layer, which can be a possible reason for the scattering of RA values but poorly affect the MR ratio itself. Our findings stress the potential of semiconductor barriers in MTJs for spintronics application that requires low RA. [ABSTRACT FROM AUTHOR]

Presents a study that analyzed the magnetic anisotropies in ultrathin films. Use of torsion oscillating magnetometry in ultrahigh vacuum; Details on a phenomenological anisotropy model that provided a useful connection between different components of surface anisotropies; Experimental method and frame of interpretation.

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

We investigated the effect of Ti substitution for Fe in Co2FeSi Heusler alloy (Co2Fe1-xTixSi) on their electronic structure, chemical ordering, and spin-dependent transport properties. First-principles calculations of the density of states (DOS) indicated that the peak just above the Fermi level in the minority-spin DOS (the conduction band edge of half-metallic gap) shifts towards higher energies with increasing Ti, leading to the enhancement in the half-metallic gap and the spin-polarization. We found in epitaxial Co2(Fe1-xTix)Si thin films that the required annealing temperature for long range L21-ordering can be substantially reduced from 650 °C for Co2FeSi to 400 °C for x ≥ 0.2. The enhancement of spin-polarization by the substitution of Fe with Ti was experimentally confirmed from anisotropic magnetoresistance measurements and spin-accumulation signals in non-local spin valve devices with the Co2Fe1-xTixSi films. [ABSTRACT FROM AUTHOR]

Ti-doped MgO (MTO) barriers were examined for polycrystalline magnetic tunnel junctions (MTJs) in combination with CoFeB ferromagnetic electrodes. The high tunneling magnetoresistance (TMR) ratio up to 240% and 160% was observed for the MTJs with Mg0.95Ti0.05O and Mg0.9Ti0.1O barriers after annealing at 450 °C. This high TMR ratio implies the presence of coherent tunneling. For a given thickness, MTJs with the MTO barriers were confirmed to have lower resistance-area product (RA) compared to those with the MgO barriers, suggesting the intrinsically lower barrier height of the MTO barriers. The MTO-based MTJs exhibit higher TMR ratio than those of the MgO-based MTJs for the RA range lower than 5 Ω µm² as a consequence of thicker barriers and better wettability. This work has demonstrated the potential of the MTO barriers for low-RA MTJs. [ABSTRACT FROM AUTHOR]

We have investigated the structure and magneto-transport properties of Co2Mn(Ge0.75Ga0.25) (CMGG) Heusler alloy thin films with near-stoichiometric and Mn-rich compositions in order to understand the effect of Co-Mn anti-sites on bulk spin polarization. Anomalous x-ray diffraction measurements using synchrotron radiated x-rays confirmed that CoMn anti-sites easily form in the near-stoichiometric CMGG compound at annealing temperature higher than 400 °C, while it can be suppressed in Mn-rich CMGG films. Accordingly, large enhancement in negative anisotropic magnetoresistance of CMGG films and giant magnetoresistance (GMR) in current-perpendicular-to-plane (CPP) pseudo spin valves were observed in the Mn-rich composition. A large resistance-area product change (ΔRA) of 12.8 mΩ µm2 was demonstrated in the CPP-GMR pseudo spin valves using the Mn-rich CMGG layers after annealing at 600 °C. It is almost twice of the maximum output observed in the CPP-GMR pseudo spin valves using the near-stoichiometric CMGG. These indicate that the spin polarization of CMGG is enhanced in the Mn-rich composition through suppressing the formation of CoMn-antisites in CMGG films, being consistent with first-principle calculation results. [ABSTRACT FROM AUTHOR]