Current-perpendicular-to-plane giant magnetoresistance using Co ₂Fe(Ga_1-xGe_x) Heusler alloy

We investigated the current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) of pseudo spin valves (PSVs) using ferromagnetic (FM) Heusler alloy Co₂Fe(Ga_1-xGe_x) (x = 0, 0.5, and 1) layers and an Ag spacer layer. The FM layer with x = 0.5 gave rise to the highest MR output, ΔRA = 8.7 mΩ·μm², at room temperature with 10 nm thick Heusler alloy layers. The MR output increased with increasing annealing temperature, T_a, with a maximum at T_a = 500 °C. Transmission electron microscopy showed no visible changes in the layered structure; however, energy dispersive x-ray analysis indicated a considerable diffusion of Ga and Ge into the other layers by annealing at T _a = 550 °C. The ΔRA dependence on the thickness of the FM layers indicated that both high bulk and interface spin asymmetries contribute to the high MR output.