Field-like spin-orbit torque associated with out-of-plane spin polarization in Py/van der Waals heterostructures

Abstract Low-symmetry van der Waals (vdW) materials have recently emerged as a fertile platform for generating unconventional spin-orbit torques (SOTs) beyond the conventional spin Hall effect (SHE) framework. Here, we report the experimental observation of a field-like torque ( $$\:{\tau\:}_{FLT}$$ ) associated with out-of-plane ( z -polarized) spin polarization in Py/WTe 2 and Py/MoTe 2 heterostructures using angle-resolved spin-torque ferromagnetic resonance. Angular symmetry analysis enables the unambiguous separation of vector torque components, revealing that the z -polarized $$\:{\tau\:}_{FLT}$$ reaches a magnitude comparable to that of the conventional in-plane damping-like torque ( $$\:{\tau\:}_{DLT}$$ ) associated with the SHE. Complementary macrospin simulations demonstrate that the inclusion of z -polarized $$\:{\tau\:}_{FLT}$$ enables fast switching of in-plane magnetization, in contrast to conventional heavy-metal-based systems. Our experimental and simulation results establish low-symmetry vdW-based heterostructures as a viable platform for generating sizable out-of-plane SOTs and achieving efficient control of in-plane magnetization.