Spin-orbit torque generated by Pd oxides

Current-induced spin-orbit torques enable the manipulation of magnetization in ultrathin ferromagnetic metals. Recent studies have revealed that the spin-orbit torques can be generated by spin-orbit coupling at ferromagnetic-metal/heavy-metal-oxide interfaces. Here, we report the generation of spin-orbit torques using Pd oxides, PdOx. Pd is known as a heavy metal with high conversion efficiency between charge and spin currents because fo the strong spin-orbit coupling. In this work, we quantified the spin-orbit torques generated by PdOx using spin-torque ferromagnetic resonance for NiFe/PdOx bilayers with various oxidation levels. The oxidation level of the PdOx layer was manipulated by varying the oxygen gas flow during the reactive sputtering. By increasing the oxidation level of the PdOx layer, we found that the damping-like torque efficiency is significantly suppressed, showing vanishingly small interface spin-orbit torques in the NiFe/PdOx bilayers. This is in stark contrast to the spin-torque generation in NiFe/PtOx bilayers, where the damping-like torque efficiency is not sensitive to the oxidation level of PtOx. Our results therefore will be essential for fundamental understanding of the spin-orbit torques generated by metal oxides.