Separation of Artifacts from Spin‐Torque Ferromagnetic Resonance Measurements of Spin‐Orbit Torque for the Low‐Symmetry Van der Waals Semi‐Metal ZrTe₃

Abstract

Spin-orbit torques generated by exfoliated layers of the low-symmetry semi-metal ZrTe 3 are measured 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 𝝃 DL || = 0.014 ± 0.004, and an unconventional in-plane field-like torque efficiency |𝝃 FL || | = 0.003 ± 0.001. The out-of-plane anti-damping torque is negligible. It is suggested that artifacts similarly interfere with the standard ST-FMR analysis for other van der Waals samples thicker than about 10 nm.

Giant room-temperature spin-orbit torque in a bismuthate superconductor

“…[ 27,28 ]. The dependence of the symmetric and antisymmetric components on φ for both longitudinal and transverse signals are shown in Fig.…”

Sagnac interferometry for high-sensitivity optical measurements of spin-orbit torque

“…The work-horse techniques for this purpose have been electrical measurements of current-induced magnetic reorientation with readout based on the magnetoresistance properties of the samples (2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19), but these have some shortcomings. One must be careful to separate thermoelectric voltages from the torque signals (20,21), and, even when performed carefully, different electrical techniques can often produce quantitatively inconsistent measurements, indicating that some may be affected by artifacts that are not yet understood (22)(23)(24)(25)(26). Furthermore, in cases when one wishes to measure SOTs acting on insulating magnetic layers, electrical measurements provide much lower signal levels compared to metallic magnets due to decreased magnetoresistance.…”