Field-Free Magnetization\nSwitching Induced by Bulk\nSpin–Orbit Torque in a (111)-Oriented CoPt Single Layer with\nIn-Plane Remanent Magnetization

Abstract

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