Spin–orbit torques (SOTs) are used to manipulate magnetization of ferromagnets in heavy metal/ferromagnetic bilayers and, thus, are technologically relevant from magnetization switching perspective. This necessitates development of methods which give an insight into SOT behavior and enable SOT efficiency estimation. In this article, we demonstrate an experimental approach of out-of-plane angle resolved Second Harmonic Hall (SHH) measurement, in Pt/Co and Ta/CoFeB perpendicular magnetic anisotropy (PMA) systems, for damping-like and field-like SOT efficiency estimation. This method reveals an angle dependent field-like term which depends on the magnetization direction in the Ta/CoFeB system. The damping-like and field-like SOT efficiencies are extracted by solving Landau–Lifshitz–Gilbert–Slonczewski equation in the low frequency limit of magnetic susceptibility. Along with SHH measurements, we also experimentally demonstrate anomalous Hall effect based spin-torque ferromagnetic resonance technique for SOT efficiency quantification in PMA systems.
Chouhan et al. (Wed,) studied this question.