Field-Free Spin Orbit Torque Switching in a Single Crystalline Ferromagnetic Semiconductor Film with Perpendicular Anisotropy

We reports observation of field-free spin-orbit torque (SOT) magnetization switching within a single layer of (Ga,Mn)(As,P) ferromagnetic film exhibiting perpendicular magnetic anisotropy. The SOT switching phenomenon is characterized by distinct transitions between two Hall resistance (HR) states during current scans. When subjected to an in-plane bias field, the observed switching chirality in the HR hysteresis loop consistently aligns with SOT induced by spin polarization stemming from Rashba- and Dresselhaus-type spin-orbit fields (SOFs) within the tensile-strained crystalline structure of (Ga,Mn)(As,P) film. Remarkably, SOT switching is demonstrated to occur even in the absence of an external bias field, with its chirality reversing according to the direction of magnetization initialization. We attribute this field-free switching to symmetry breaking facilitated by an internal coupling field, the orientation of which is decided by the external field experienced during magnetization initialization. Further evidence supporting the presence of this coupling field includes a shift in the field-scan HR hysteresis depending on the direction of magnetization initialization. Structural analysis reveals a surface layer enriched in Mn and O, indicating the presence of oxide-based magnetic structures that are magnetically coupled with the (Ga,Mn)(As,P) film. The temperature dependence of field-free SOT switching corroborates this explanation, as the internal coupling field disappears above 40 K, consistent with the expected magnetic transition in the Mn₃O₄ structure. Our discovery of field-free SOT magnetization switching in a single-layer film represents a significant advancement, offering a novel pathway for the development of simpler and more energy-efficient spintronic devices.