Determination of spin-orbit torques by thickness-dependent spin-orbit torque FMR measurement

TL;DR

This paper introduces a thickness-dependent SOT-FMR measurement method to accurately characterize spin-orbit torques in Fe/Pt bilayers, addressing challenges posed by field-like torque and Oersted torque interference.

Contribution

It proposes a novel, self-calibrated SOT-FMR technique leveraging thickness dependence to distinguish different spin-orbit torque components.

Findings

Field-like torque significantly affects SOT measurements.

Thickness dependence helps differentiate torque components.

Proposed method improves accuracy of spin Hall angle estimation.

Abstract

Current induced spin-orbit torques (SOTs) in Fe/Pt bilayers have been investigated utilizing the spin-orbit torque ferromagnetic resonance (SOT-FMR) measurement. Characterization of thin films with different thicknesses indicates existence of a sizable field-like spin-orbit torque competing with the Oersted field induced torque (Oersted torque). The field-like torque is neglected in the standard SOT-FMR method and the presence of a strong field-like torque makes estimation of the spin Hall angle (SHA) problematic. Also, it is challenging to differentiate the field-like torque from the Oersted torque in a radiofrequency measurement. Based on the thickness dependence of field-like torque, anti-damping torque, and Oersted torque, the thickness-dependent SOT-FMR measurement is proposed as a more reliable, self-calibrated approach for characterization of spin-orbit torques.