Harnessing Pt/W spin Hall superlattices for efficient field-free spin–orbit torque switching

Spin–orbit torque (SOT) offers a promising route to achieve energy-efficient magnetization switching. However, materials with a perpendicular magnetic anisotropy (PMA) require an external magnetic field for deterministic magnetization switching. Achieving SOT-driven field-free switching of PMA materials is crucial for next-generation spintronic devices. Here, we demonstrate the field-free SOT switching in [Pt/W]n/Co heterostructures using Pt/W multilayers. The competing spins from the Pt and W bilayer generate an out-of-plane SOT field that enables magnetization switching without the need for an external in-plane magnetic field. These multilayers generate unconventional spin currents, as confirmed by anomalous Hall resistance loop-shift measurements. We observed a maximum field-free switching of 92% in domain wall devices. In addition, the sample with 7 bilayers exhibits a 2.7-fold enhanced damping-like efficiency compared to a single Pt layer. This work advances practical SOT device development and deepens understanding of deterministic perpendicular magnetization switching.