Spin-orbit torques originating from bulk and interface in pt-based structures

The origin of spin-orbit torques in prototypical Pt-based spintronic devices strongly depends on the choice of the ferromagnetic layer. We show that, in a Pt/Ni bilayer, the bulk spin Hall effect in the Pt layer is responsible for both damping-like and field-like torques. In contrast, the interfacial spin-orbit coupling dominates the damping-like torque in a Pt/Fe bilayer, where the Ni layer is replaced with Fe, despite the strong spin Hall effect in the Pt layer. The reason for this is that the strong spin-orbit coupling at the Pt/Fe interface generates the sizable damping-like torque, while it suppresses the damping-like torque arising from the bulk through the dissipation of the spin Hall current at the interface. Although the bulk spin Hall effect plays a minor role in the generation of the damping-like torque in the Pt/Fe bilayer, the bulk effect is significant in the generation of the field-like torque, which arises from a rotation of the spin direction of the spin Hall current at the Pt/Fe interface. We found that the direction of the field-like torque originating from the spin Hall effect is opposite between the Pt/Ni and Pt/Fe bilayers. This difference is attributed to the opposite sign of the imaginary part of the spin-mixing conductance due to different spin-dependent potentials at the Pt/Ni and Pt/Fe interfaces. These results show that the bulk spin-orbit torques, as well as the interfacial spin-orbit torques, can be controlled by the interface engineering.