Spin pumping and large field-like torque at room temperature in sputtered amorphous WTe$_{2-x}$ films

We studied the spin-to-charge and charge-to-spin conversion at room temperature in sputtered WTe2-x (x=0.8)(t)/Co20Fe60B20(6 nm) heterostructures. Spin pumping measurements were used to characterize the spin-to-charge efficiency and the spin efficiency was calculated to be larger than ~0.035. Second harmonic Hall measurements were carried out to estimate the charge-to-spin conversion ratio. We found that the system exhibits a large field-like-torque (spin torque efficiency ~ 0.1) and small damping-like-torque (spin torque efficiency ~0.001) compared to that reported for heavy metals. High-resolution transmission electron microscopy images show that the WTe2-x layer is amorphous, which may enhance the spin swapping effect by inducing large interfacial spin orbit scattering, thus contributing to a large field like torque.