Voltage-circuit analysis in spin-torque ferromagnetic resonance

Abstract

Spin-orbit torque (SOT) enables efficient control of magnetization via spin-orbit coupling effects, so that accurate quantification of its efficiency is crucial for the development of spin-orbit devices. Among various characterization techniques, spin-torque ferromagnetic resonance (ST-FMR) provides a powerful method to quantify SOT. However, conventional analysis methods-such as voltage ratio analysis and DC modulation-often suffer from the limited accuracy due to uncertainties in RF current estimation. In this study, we propose a voltage-based circuit analysis that directly utilizes the measured ST-FMR signals, including parasitic effects, such as RF power loss, modulation factors, and parasitic shunting. Self-consistent checks and measurements on various heterostructures confirm that our approach yields SOT efficiencies consistent with those obtained from conventional methods. Furthermore, substrate-dependent variations are resolved by applying parasitic correction, validating the robustness of our analysis. This work provides an accurate and practical methodology for evaluating SOT efficiency of spin-orbit materials.