All-optical Vector Measurement of Spin-Orbit-Induced Torques Using both Polar and Quadratic Magneto-optic Kerr Effects

We demonstrate that the magneto-optic-Kerr effect with normal light incidence can be used to obtain quantitative optical measurements of both components of spin-orbit-induced torque (both the antidamping and effective-field components) in heavy-metal/ferromagnet bilayers. This is achieved by analyzing the quadratic Kerr effect as well as the polar Kerr effect. The two effects can be distinguished by properly selecting the polarization of the incident light. We use this all-optical technique to determine the spin-orbit torques generated by a series of Pt/Permalloy samples, finding values in excellent agreement with spin-torque ferromagnetic resonance measurements. Work at Delaware was supported by the Semiconductor Research Corporation through the Center for Nanoferroic Devices and the NSF (DMR-1505192). Work at Cornell was supported by DARPA (N66001-11-1-4110) and the NSF (DMR-1010768). This research was performed in part at the Cornell NanoScale Facility, a node of the National Nanotechnology Infrastructure Network (NNIN), which is supported by the NSF (ECCS-0335765), and in the facilities of the NSF/MRSEC-funded Cornell Center for Materials Research (DMR-1120296)