Unconventional spin-orbit torques from sputtered MoTe2 films

Abstract

Materials with strong spin-orbit coupling and low crystalline symmetry are promising for generating large unconventional spin-orbit torques (SOTs), such as in-plane fieldlike (FL) torques and out-of-plane dampinglike (DL) torques, which can effectively manipulate and deterministically switch an out-of-plane magnetization without the need for additional external in-plane magnetic fields. Here, we report SOTs generated by magnetron-sputtered $1T^{\prime }{\mathrm{MoTe}}_2$/Permalloy (Py; ${\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}$)/MgO heterostructures using both spin-torque ferromagnetic resonance (ST-FMR) and second harmonic Hall measurements. We observed unconventional FL and DL torques in our samples due to spins polarized normal to the interface of ${\mathrm{MoTe}}_2$ and Py layers, and studied the influence of crystallographic order and ${\mathrm{MoTe}}_2$ layer thickness on the SOTs. By comparing the Raman spectra of $1T^{\prime }{\mathrm{MoTe}}_2$ samples prepared in different ways, we found a tensile strain in sputtered ${\mathrm{MoTe}}_2$ films, which might further enhance the generation of unconventional torques by reducing the symmetry of $1T^{\prime }{\mathrm{MoTe}}_2$.