Separation of Artifacts from Spin-Torque Ferromagnetic Resonance Measurements of Spin-Orbit Torque for the Low-Symmetry van der Waals Semi-Metal ZrTe${}_{\text{3}}$

Abstract

We measure spin-orbit torque generated by exfoliated layers of the low-symmetry semi-metal ZrTe${}_3$ using the spin-torque ferromagnetic resonance (ST-FMR) technique. When the ZrTe${}_3$ has a thickness greater than about 10 nm, artifacts due to spin pumping and/or resonant heating can cause the standard ST-FMR analysis to overestimate the true magnitude of the torque efficiency by as much as a factor of 30, and to indicate incorrectly that the spin-orbit torque depends strongly on the ZrTe${}_3$ layer thickness. Artifact-free measurements can still be achieved over a substantial thickness range by the method developed recently to detect ST-FMR signals in the Hall geometry as well as the longitudinal geometry. ZrTe${}_3$/Permalloy samples generate a conventional in-plane anti-damping spin torque efficiency ${\xi }_{||}^{\text{DL}}$ = 0.014 $\pm$ 0.004, and an unconventional in-plane field-like torque efficiency $|{\xi }_{||}^{\text{FL}}|$ = 0.003 $\pm$ 0.001. The out-of-plane anti-damping torque is negligible. We suggest that artifacts similarly interfere with the standard ST-FMR analysis for other van der Waals samples thicker than about 10 nm.

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Cited by in corpus (2)

• Substrate-induced spin-torque-like signal in spin-torque ferromagnetic resonance measurement
• Giant spin torque efficiency in naturally oxidized polycrystalline TaAs thin films