Field-Free Magnetization Switching Induced by Bulk Spin-Orbit Torque in a (111)-Oriented CoPt Single Layer with In-Plane Remanent Magnetization

Spin-orbit torque (SOT)-induced perpendicular magnetization switching is one of the key solutions for the next generation of magnetic memory and spin logic applications. Recently, the bulk SOT effect in a single magnetic layer with a vertical composition gradient has attracted a lot of attention because it can break through the interfacial nature of the SOT effect in a traditional bilayer structure. However, the dependency of the external in-plane magnetic field or the additional pinning layer for deterministic switching hinders the further application of this technology. Here, for the first time, we implement field-free magnetization switching induced by bulk SOT in a single (111)-oriented CoPt magnetic layer with in-plane remanent magnetization. The initialized longitudinal in-plane remanent magnetization can substitute the external magnetic field to break the inversion symmetry and realize continuous field-free perpendicular magnetization switching. Furthermore, the in-plane remanent magnetization can be manipulated by the SOT effective field induced by lateral current pulses, leading to a tunable switching chirality. A multi-domain micromagnetic model is established to describe in depth the experimental observations and clarify the relationship between switching amplitude and easy magnetization cone angle. Our work provides an alternative solution to realize field-free perpendicular magnetization switching in a single magnetic layer, which can promote the development of emerging high-density and low-power SOT-based devices.