Highly accurate evaluation of spin-torque efficiency by measuring in-plane angular dependence of spin-torque ferromagnetic resonance

•We developed a reliable method to evaluate spin torque efficiency precisely.•It is hard to eliminate an asymmetric Oersted field even in a symmetric sample.•In-plane angular dependence of ST-FMR must be measured to improve the precision.•The scattering of evaluation can be reduced remarkably from 80% to 5%. Spin-torque ferromagnetic resonance (ST-FMR) is a powerful tool to evaluate spin-torque efficiency (ξFMR), the efficiency of current-induced torque in metallic bilayers consisting of ferromagnetic and nonmagnetic materials. In general, ξFMR can be evaluated from the amplitude ratio between symmetric and anti-symmetric components of the ST-FMR spectrum. However, the ratio is also affected by an unnecessary magnetic field owing to the asymmetric alternating current flow used to excite the ST-FMR. In this article, we demonstrate that ξFMR can be precisely evaluated from the full-angular dependence of the ST-FMR spectrum even though the distribution of alternating current flow is highly asymmetric.