Orbital Hall effect assisted field-free perpendicular magnetization switching

Spin–orbit torques (SOTs) generated through the conventional spin Hall effect (SHE) and/or Rashba–Edelstein effect offer potential for magnetization manipulation. However, deterministic switching of perpendicular ferromagnets via SOTs requires a strong symmetry-breaking perturbation, typically an external magnetic field. Here, we demonstrate that field-free SOT switching of perpendicular magnetization can be facilitated with the assistance of the orbital Hall effect (OHE). Using a representative Co/PtGd bilayer SOT device, we find that while the planar Hall effect (PHE) generates a finite out-of-plane damping-like torque, representing a lateral symmetry-breaking effect, the SHE-induced torque achievable at practical current densities is insufficient to switch the perpendicular magnetization. Incorporating a Mo underlayer and exploiting its strong OHE can amplify the in-plane damping-like torque via orbital-to-spin conversion, enabling efficient field-free deterministic switching without complex device geometries or low-symmetric spin sources, providing a straightforward, scalable strategy for high-speed, low-power spintronics.