Stacking-Order Effect on Spin-Orbit Torque, Spin Hall Magnetoresistance, and Magnetic Anisotropy in Ni81Fe19-Ir O2 Bilayers

Abstract

The 5d transition-metal oxides are an intriguing platform to demonstrate efficient charge-to-spin-current conversion due to a unique electronic structure dominated by strong spin-orbit coupling. Here, we report on the stacking-order effect of spin-orbit torque (SOT), spin-Hall magnetoresistance, and magnetic anisotropy in bilayer Ni81Fe19-5d iridium oxide, IrO2. While all IrO2 and Pt control samples exhibit large dampinglike SOT generation, stemming from the efficient charge-to-spin-current conversion, the magnitude of the SOT is larger in the IrO2(Pt) bottom sample than in the IrO2(Pt) top one. The fieldlike SOT has an even more significant stacking-order effect, resulting in an opposite sign in the IrO2 samples in contrast to the same sign in the Pt samples. Furthermore, we observe that the magnetic anisotropy energy density and the anomalous Hall effect are increased in the IrO2(Pt) bottom sample, suggesting enhanced interfacial perpendicular magnetic anisotropy. Our findings highlight the significant influence of the stacking order on spin transport and the magnetotransport properties of Ir oxide-ferromagnet systems, providing useful information for the design of SOT devices, including 5d transition-metal oxides.