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Spin–Orbit Torques in NbSe 2 /Permalloy Bilayers

2018; American Chemical Society; Volume: 18; Issue: 2 Linguagem: Inglês

10.1021/acs.nanolett.7b04993

1530-6992

Marcos H. D. Guimarães, Gregory M. Stiehl, David MacNeill, Neal Reynolds, Daniel C. Ralph,

Physics of Superconductivity and Magnetism

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.