We study current-induced torques in ${\mathrm{WTe}}_2$/permalloy bilayers as a function of ${\mathrm{WTe}}_2$ thickness. We measure the torques using both second-harmonic Hall and spin-torque ferromagnetic resonance techniques for samples with ${\mathrm{WTe}}_2$ thicknesses that span from 16 nm down to a single monolayer. We confirm the existence of an out-of-plane antidamping torque, and we show directly that the sign of this torque component is reversed across a monolayer step in the ${\mathrm{WTe}}_2$. The magnitude of the out-of-plane antidamping torque depends only weakly on ${\mathrm{WTe}}_2$ thickness, such that even a single-monolayer ${\mathrm{WTe}}_2$ device provides a strong torque that is comparable to much thicker samples. In contrast, the out-of-plane fieldlike torque has a significant dependence on the ${\mathrm{WTe}}_2$ thickness. We demonstrate that this fieldlike component originates predominantly from the Oersted field, thereby correcting a previous inference drawn by our group based on a more limited set of samples.

• Received 10 July 2017

DOI:https://doi.org/10.1103/PhysRevB.96.054450