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

Abstract

We investigate spin-orbit torques in prototypical Pt-based spintronic devices. We find that, in Pt/Ni and Pt/Fe bilayers, the dampinglike torque efficiency depends on the thickness of the Pt layer. We also find that the dampinglike torque efficiency is almost identical in the Pt/Ni and Pt/Fe bilayers despite the stronger spin memory loss at the Pt/Fe interface. These results suggest that although the dominant source of the dampinglike torque is the bulk spin Hall effect in the Pt layer, a sizable dampinglike torque is generated by the interface in the Pt/Fe bilayer due to the stronger interfacial spin-orbit coupling. In contrast to the dampinglike torque, whose magnitude and sign are almost identical in the Pt/Ni and Pt/Fe bilayers, the fieldlike torque strongly depends on the choice of the ferromagnetic layer. The sign of the fieldlike torque originating from the bulk spin Hall effect in the Pt layer is opposite between the Pt/Ni and Pt/Fe bilayers, which can be attributed to the opposite sign of the imaginary part of the spin-mixing conductance. These results demonstrate that the spin-orbit torques are quite sensitive to the electronic structure of the ferromagnet layer.