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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 ${\mathrm{Ni}}_{81}{\mathrm{Fe}}_{19}$-5d iridium oxide, ${\mathrm{Ir}\mathrm{O}}_{2}$. While all ${\mathrm{Ir}\mathrm{O}}_{2}$ and $\mathrm{Pt}$ 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 ${\mathrm{Ir}\mathrm{O}}_{2}$($\mathrm{Pt})$ bottom sample than in the ${\mathrm{Ir}\mathrm{O}}_{2}$($\mathrm{Pt})$ top one. The fieldlike SOT has an even more significant stacking-order effect, resulting in an opposite sign in the ${\mathrm{Ir}\mathrm{O}}_{2}$ samples in contrast to the same sign in the $\mathrm{Pt}$ samples. Furthermore, we observe that the magnetic anisotropy energy density and the anomalous Hall effect are increased in the ${\mathrm{Ir}\mathrm{O}}_{2}$($\mathrm{Pt})$ 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 $\mathrm{Ir}$ oxide-ferromagnet systems, providing useful information for the design of SOT devices, including 5d transition-metal oxides.

The $5d$ transition-metal oxides have a unique electronic structure dominated by strong spin-orbit coupling and hence they can be an intriguing platform to explore spin-current physics. Here, we report on room-temperature generation of spin-orbit torque (SOT) from a conductive $5d$ iridium oxide, $\mathrm{Ir}{\mathrm{O}}_{2}$. By measuring second-harmonic Hall resistance of ${\mathrm{Ni}}_{81}{\mathrm{Fe}}_{19}/\mathrm{Ir}{\mathrm{O}}_{2}$ bilayers, we find both dampinglike and fieldlike SOTs. The former is larger than the latter, enabling easier control of magnetization. We also observe that the dampinglike SOT efficiency has a significant dependence on $\mathrm{Ir}{\mathrm{O}}_{2}$ thickness, which is well described by the drift-diffusion model based on the bulk spin Hall effect. We deduce the effective spin Hall angle of +0.093 \ifmmode\pm\else\textpm\fi{} 0.003 and the spin-diffusion length of 1.7 \ifmmode\pm\else\textpm\fi{} 0.2 nm. By comparison with control samples Pt and Ir, we show that the effective spin Hall angle of $\mathrm{Ir}{\mathrm{O}}_{2}$ is comparable to that of Pt and seven times higher than that of Ir. The fieldlike SOT efficiency has a negative sign without appreciable dependence on the thickness, in contrast to the dampinglike SOT. This suggests that the fieldlike SOT likely stems from the interface. These experimental findings suggest that the uniqueness of the electronic structure of $5d$ transition-metal oxides is crucial for highly efficient charge to spin-current conversion.

The temperature dependence of spin-orbit torques (SOTs) and spin-dependent transport parameters is measured in bilayer Ta/TbCo ferrimagnetic alloy films with bulk perpendicular magnetic anisotropy. We find that the dampinglike (DL)-SOT effective field diverges as temperature is swept through the magnetic compensation temperature (${T}_{\mathrm{M}}$), where the net magnetization vanishes due to the opposing contributions from the Tb and Co sublattices. We show that DL-SOT scales with the inverse of the saturation magnetization (${M}_{\mathrm{s}}$), whereas the spin-torque efficiency is independent of the temperature-dependent ${M}_{\mathrm{s}}$. Our findings provide insight into spin transport mechanisms in ferrimagnets and highlight low-${M}_{\mathrm{s}}$ rare-earth/transition-metal alloys as promising candidates for SOT device applications.

We investigate the in-plane field dependence of current-induced magnetic domain wall motion in asymmetric Co/Ni nanowires. The application of an in-plane field changed the direction of domain wall motion. In a systematic study, by varying the magnetic layer thickness, we show that the in-plane field induces a crossover from spin Hall torque to adiabatic spin-transfer torque for the magnetic domain wall motion. Furthermore, the dependence of the threshold current density on the in-plane longitudinal field provides a way for determining the strength of the Dzyaloshinskii-Moriya interaction.