Enhancement of magnetoresistance by inserting thin NiAl layers at the interfaces in Co₂FeGa_0.5Ge_0.5/Ag/Co₂FeGa_0.5Ge_0.5 current-perpendicular-to-plane pseudo spin valves

We have investigated the effects of insertion of a thin NiAl layer (≤0.63 nm) into a Co₂FeGa_0.5Ge_0.5 (CFGG)/Ag interface on the magnetoresistive properties in CFGG/Ag/CFGG current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) pseudo spin valves (PSVs). First-principles calculations of ballistic transmittance clarified that the interfacial band matching at the (001)-oriented NiAl/CFGG interface is better than that at the (001)-Ag/CFGG interface. The insertion of 0.21-nm-thick NiAl layers at the Co₂FeGa_0.5Ge_0.5/Ag interfaces effectively improved the magnetoresistance (MR) output; the observed average and the highest MR ratio (ΔRA) are 62% (25 mΩ μm²) and 77% (31 mΩ μm²) at room temperature, respectively, which are much higher than those without NiAl insertion. Microstructural analysis using scanning transmission electron microscopy confirmed the existence of thin NiAl layers at the Ag interfaces with only modest interdiffusion even after annealing at 550 °C. The improvement of the interfacial spin-dependent scattering by very thin NiAl insertion can be a predominant reason for the enhancement of the MR output.