Structure and magnetoresistive properties of current-perpendicular-to-plane pseudo-spin valves using polycrystalline Co2Fe-based Heusler alloy films

We report current-perpendicular-to-plane giant magnetoresistance (CPP–GMR) of pseudo-spin valves (PSVs) with polycrystalline Co2Fe(Al0.5Si0.5) (CFAS) and Co2Fe(Ga0.5Ge0.5) (CFGG) Heusler alloy films. Strongly [0 1 1] textured polycrystalline Heusler alloy films grew on the Ta/Ru/Ag underlayer. Relatively large CPP–GMR values of ΔRA up to 4 mΩ μm2 and ΔR/R up to 10% were obtained with 5 nm thick Heusler alloy films and Ag spacer layer by annealing CFAS PSV at 450 °C and CFGG PSV at 350 °C. Transmission electron microscopy revealed a flat and sharp interface between the [0 1 1] textured CFAS layers and the [1 1 1] textured Ag spacer layer. Annealing above an optimal temperature for each PSV led to reductions in MR values as a result of the thickening of the spacer layer induced by the Ag diffusion from the outer Ag layers.