Resolving Discrepancies in Spin-Torque Ferromagnetic Resonance Measurements: Lineshape versus Linewidth Analyses

When spin-orbit torques are measured using spin-torque ferromagnetic resonance, two alternative ways of analyzing the results to extract torque efficiencies---lineshape analysis and change in linewidth versus direct current---often give inconsistent results. We identify a source for these inconsistencies. show that fits resonance data standard framework leave significant residuals we as due (i) current-induced excitations small volume magnetic material with damping much larger than bulk layer, which speculate is associated heavy-metal--magnet interface (ii) oscillations sample magnetization at modulation frequency heating. The dependence residual signals on current can interfere an accurate extraction efficiencies by method. discrepancies between types be largely eliminated extrapolation window fields used values so minimize influence signals.