Current perpendicular-to-plane giant magnetoresistance devices using half-metallic Co₂Fe_0.4Mn_0.6Si electrodes and a Ag-Mg spacer

Current perpendicular-to-plane (CPP) giant magnetoresistance (GMR) effects in devices including Co₂Fe_0.4Mn_0.6Si (CFMS)/Ag_100-xMg_x/CFMS structures were investigated theoretically and experimentally. First-principles transport calculation revealed that the Fermi surface matching between CFMS and L1₂ Ag₃Mg is better than that between CFMS and fcc-Ag. In the experiments the Mg composition, x was changed from 0 to 26 at.%, in which both face centered cubic phase and L1₂ phase of Ag-Mg alloys are included depending on the Mg composition. It was confirmed by a cross-sectional high-angle annular dark field scanning transmission electron microscope (HAADF-STEM) image that the Ag-Mg spacer layer with L1₂ ordered phase was successfully fabricated for x = 22 at.%. The maximum CPP-GMR ratio and the change of the areal resistance () were 56% and 20 mm², respectively, for x = 22 at.% at room temperature, which is much higher than that of the conventionally used pure Ag spacer devices. It was suggested from the HAADF-STEM images and the results of the temperature dependence of CPP-GMR effects that the diffusion of Mn atoms occurred less at the CFMS/Ag-Mg interfaces for the L1₂ ordered Ag-Mg spacer devices than the Ag spacer devices, which might be a key factor for the enhancement of the value. The newly developed L1₂ Ag-Mg spacer is a promising material for realizing large of the CPP-GMR devices.