Spin-orbit torques in NbSe$_2$/Permalloy bilayers

• Main Authors: Guimaraes, Marcos H. D, Stiehl, Gregory M, MacNeill, David, Reynolds, Neal D, Ralph, Daniel C
• Format: Journal Article
• Language: English
• Published: 22-01-2018
• Subjects: Physics - Mesoscale and Nanoscale Physics
• DOI: 10.48550/arxiv.1801.07281

Nano Letters (2018) We present measurements of current-induced spin-orbit torques generated by
NbSe$_2$, a fully-metallic transition-metal dichalcogenide material, made using
the spin-torque ferromagnetic resonance (ST-FMR) technique with
NbSe$_{2}$/Permalloy bilayers. In addition to the out-of-plane Oersted torque
expected from current flow in the metallic NbSe$_{2}$ layer, we also observe an
in-plane antidamping torque with torque conductivity $\sigma_{S} \approx 10^{3}
(\hbar / 2e)$($\Omega$m)$^{-1}$ and indications of a weak field-like
contribution to the out-of-plane torque oriented opposite to the Oersted
torque. Furthermore, in some samples we also measure an in-plane field-like
torque with the form $\hat{m} \times \hat{z}$, where $\hat{m}$ is the Permalloy
magnetization direction and $\hat{z}$ is perpendicular to the sample plane. The
size of this component varies strongly between samples and is not correlated
with the NbSe$_{2}$ thickness. A torque of this form is not allowed by the bulk
symmetries of NbSe$_{2}$, but is consistent with symmetry breaking by a
uniaxial strain that might result during device fabrication.