New materials research for high spin polarized current

The author reports here a thorough investigation of structural and magnetic properties of Co ₂FeAl _0.5Si _0.5 Heusler alloy films, and the tunnel magnetoresistance effect for junctions with Co ₂FeAl _0.5Si _0.5 electrodes, spin injection into GaAs semiconductor from Co ₂FeAl _0.5Si _0.5, and spin filtering phenomena for junctions with CoFe ₂O ₄ ferrite barrier. It was observed that tunnel magnetoresistance ratio up to 832%(386%) at 9 K (room temperature), which corresponds to the tunnel spin polarization of 0.90 (0.81) for the junctions using Co ₂FeAl _0.5Si _0.5 Heusler electrodes by optimizing the fabrication condition. It was also found that the tunnel magnetoresistance ratio are almost the same between the junctions with Co ₂FeAl _0.5Si _0.5 Heusler electrodes on Cr buffered (1 0 0) and (1 1 0) MgO substrates, which indicates that tunnel spin polarization of Co ₂FeAl _0.5Si _0.5 for these two direction are almost the same. The next part of this paper is a spin filtering effect using a Co ferrite. The spin filtering effect was observed through a thin Co-ferrite barrier. The inverse type tunnel magnetoresistance ratio of -124% measured at 10 K was obtained. The inverse type magnetoresistance suggests the negative spin polarization of Co-ferrite barrier. The magnetoresistance ratio of -124% corresponds to the spin polarization of -0.77 by the Co-ferrite barrier. The last part is devoted to the spin injection from Co ₂FeAl _0.5Si _0.5 into GaAs. The spin injection signal was clearly obtained by three terminal Hanle measurement. The spin relaxation time was estimated to be 380 ps measured at 5 K.