Enhanced current-perpendicular-to-plane giant magnetoresistance by improvement of atomic order of Co2FeSi Heusler alloy film through Ag doping

We investigated the effect of Ag doping on atomic order and spin polarization of Co2FeSi Heusler alloy thin films. The Co2FeSi film doped with 3at.%-Ag showed improved degree of B2- and L21-ordering after thermal annealing comparing to Co2FeSi film. Negative sign of anisotropic magnetoresistance suggests the half-metallic nature of Ag-doped Co2FeSi film after annealing at a relatively low temperature of 300 °C. The current-perpendicular-to-plane pseudo spin-valves using the Ag-doped Co2FeSi ferromagnetic (FM) electrodes showed about 1.2 times larger MR ratio than that using the Co2FeSi FM electrodes, reflecting an enhanced spin polarization in Ag-doped Co2FeSi film. Micro-structure analysis revealed the doped Ag was rejected out of Co2FeSi layer after annealing. This study suggests Ag doping to Co-based Heusler compound having no/few solubility with Ag is beneficial for realizing spin-valves with high output at moderate annealing conditions.