Robust Field-Free Switching Using Large Unconventional Spin-Orbit Torque in an All-Van der Waals Heterostructure

The emerging all-van der Waals (vdW) magnetic heterostructure provides a new platform to control the magnetization by the electric field beyond the traditional spintronics devices. One promising strategy is using unconventional spin-orbit torque (SOT) exerted by the out-of-plane polarized spin current to enable deterministic magnetization switching and enhance the switching efficiency. However, in all-vdW heterostructures, large unconventional SOT remains elusive and the robustness of the field-free switching against external magnetic field has not been examined, which hinders further applications. Here, the study demonstrates the field-free switching in an all-vdW heterostructure combining a type-II Weyl semimetal TaIrTe₄ and above-room-temperature ferromagnet Fe₃GaTe₂. The fully field-free switching can be achieved at 2.56 × 10¹⁰ A m^-2 at 300 K and a large SOT effective field efficiency of the out-of-plane polarized spin current generated by TaIrTe₄ is determined to be 0.37. Moreover, it is found that the switching polarity cannot be changed until the external in-plane magnetic field reaches 252 mT, indicating a robust switching against the magnetic field. The numerical simulation suggests the large unconventional SOT reduces the switching current density and enhances the robustness of the switching. The work shows that all-vdW heterostructures are promising candidates for future highly efficient and stable SOT-based devices.