Phase dominance and compositional disorder effects in Cu–Zn spacer alloys for spin-dependent transport in Co2FeGa0.5Ge0.5-based junctions: A first-principles study

Abstract

Compositional disorder plays a critical role in determining transport properties in spintronic heterostructures and ultimately governs their experimentally realizable performance. In this work, we investigate spin-dependent transport in current-perpendicular-to-plane (CPP) giant magnetoresistance (GMR) junctions composed of Co2FeGa0.5Ge0.5 (CFGG) electrodes and Cu–Zn spacer alloys, with particular emphasis on the effects of spacer composition and atomic order–disorder. The virtual crystal approximation is employed to treat compositional disorder in the Cu–Zn spacer, thereby extending its application from bulk alloys to spacer alloys embedded in magnetic junctions. Systematic first-principles transport calculations reveal that the majority-spin conductance in the parallel magnetic configuration is maximized at Zn concentrations of approximately 30–50 at. % for both B2-ordered and A2-disordered spacers. This enhancement originates from improved Fermi-surface matching between the CFGG electrodes and the Cu–Zn spacer, leading to an increased interfacial spin-asymmetry coefficient and, consequently, enhanced magnetoresistance performance. In addition, both the conductance and the interfacial exchange stiffness constant exhibit only weak sensitivity to the B2 → A2 transition, indicating that atomic disorder induces only marginal changes in majority-spin transport. These results demonstrate the disorder tolerance of CFGG/Cu–Zn/CFGG junctions with respect to the Fermi-surface matching and the thermal fluctuation, and they provide design guidelines for chemically tunable spacer alloys in CPP-GMR devices.