Kavli Affiliate: Daniel C. Ralph
| First 5 Authors: Thow Min Cham, Saba Karimeddiny, Vishakha Gupta, Joseph A. Mittelstaedt, Daniel C. Ralph
| Summary:
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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