Influence of the spin pumping induced inverse spin Hall effect on spin-torque ferromagnetic resonance measurements

Spin-torque ferromagnetic resonance (ST-FMR) has been widely used to determine the spin-orbit torque (SOT) efficiency in ferromagnet/heavy-metal bilayer systems. The flow of a radio frequency current through heavy-metal generates an oscillating SOT and Oersted field, resulting in the resonance of the adjacent ferromagnetic layer and subsequent dc voltage due to the rectification effect. The dynamics of the ferromagnet, however, also pumps a spin current back into the heavy-metal. Wherein, an additional contribution to the dc voltage arises from the inverse spin Hall effect (ISHE). The spin pumping-induced ISHE (SP-ISHE) and ST-FMR voltages typically have identical symmetry. In this work, we develop a method to quantitatively obtain the SP-ISHE voltage from the ST-FMR signal in the Py(Ni80Fe20)/Pt bilayer. We find it has the opposite sign to the symmetric component of ST-FMR voltage. After this correction, both the damping-like and field-like-torque efficiency in the Py/Pt bilayer are further estimated through the Py-thickness-dependent measurements.

Automated summary

In this study, we introduce a method to quantitatively determine the spin pumping-induced inverse spin Hall effect (SP-ISHE) voltage using the ST-FMR signal in the Py(Ni80Fe20)/Pt bilayer. The SP-ISHE voltage is found to have an opposite sign to the symmetric component of the ST-FMR voltage. After correction, the efficiency of both damping-like and field-like torques in the Py/Pt bilayer is further estimated based on Py thickness-dependent measurements.