Energy-efficient field-free switching by orbital torque and spin-reorientation.

Spin-orbit torque has emerged as a leading strategy for low-power magnetisation switching in modern spintronics. To date, most efforts have focused on boosting spin currents via the spin Hall effect, exploiting only the electron's spin while largely ignoring its orbital angular momentum. Meanwhile, deterministic switching of perpendicular magnetic anisotropy layers typically requires an external in-plane field to break inversion symmetry, adding power overhead and hindering large-scale deployment. Here, we demonstrate energy-efficient field-free magnetisation switching enabled by spin reorientation in a synthetic antiferromagnetic structure and enhanced by orbital torque. By tuning the exchange coupling field and magnetic anisotropy of the synthetic antiferromagnetic samples, we achieved a magnetisation switching of 96% utilising both spin and orbital torque. Furthermore, increasing the orbital Hall layer thickness by 15 nm leads to an 85% enhancement of damping-like torque efficiency compared to the reference sample with a Pt layer as the spin source. These results demonstrate orbital angular momentum transport as an efficient torque-generation mechanism in synthetic antiferromagnetic heterostructures, offering a scalable route toward low-power spintronic devices.