5d transition-metal oxides have a unique electronic structure dominated by strong spinorbit 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 IrO2. By measuring second harmonic Hall resistance of Ni81Fe19/IrO2 bilayers, we find both dampinglike and fieldlike SOTs. The former is larger than the latter, enabling an easier control of magnetization. We also observe that the dampinglike SOT efficiency has a significant dependence on IrO2 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 ± 0.003 and the spindiffusion length of 1.7 ± 0.2 nm. By the comparison with control samples Pt and Ir, we show that the effective spin Hall angle of IrO2 is comparable to that of Pt and 7 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 is likely stemming from the interface. These experimental findings suggest that the uniqueness of electronic structure of 5d transition-metal oxides is crucial for highly efficient charge to spin current conversion.
We study spin Hall magnetoresistance (SMR) in Pt/ferrimagnetic insulator Y3Fe5O12 (YIG) bilayers by focusing on crystallinity, magnetization, and interface roughness by controlling post-annealing temperatures. The SMR in the Pt/YIG grown on Si substrate is comparable to that grown on widely used Gd3Ga5O12 substrate, indicating that the large SMR can be achieved irrespective of the crystallinity. We deduced the spin mixing conductance from the Pt thickness dependence of the SMR to find the high interface quality of the optimized Pt/YIG grown on Si in terms of spin current. We also clarified that the SMR correlates well with the magnetization, the interface roughness, and carrier density. These findings highlight that optimizing YIG properties is a key to control of magnetization by spin current, leading to the development of the low power consumption spintronic device based on the magnetic insulator.
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