Field-free magnetization switching induced by the unconventional spin–orbit torque from WTe2

Spin–orbit torque provides a highly efficient way to achieve current-induced magnetization switching, which relies on charge-to-spin conversion of the spin source layer. However, in the conventional heavy metal/ferromagnetic layer, the generated spin–orbit torque is limited to in-plane, which cannot deterministically switch the perpendicularly magnetized ferromagnets, and thus impedes practical application for high-density magnetic memory. In this work, deterministic switching of perpendicular magnetization is achieved in the SrRuO3/WTe2 bilayer structure, which is attributed to the out-of-plane spin polarization originated from the van der Waals material WTe2. The out-of-plane spin polarization is further confirmed by the shift of the anomalous Hall effect loop. Spin polarization matrix analysis indicates that the reduced crystal symmetry in WTe2 is responsible for the out-of-plane spin polarization.