Field‐Free Switching of Spin–Orbit Torque Magnetic Devices via Symmetry Breaking: An Overview and Outlook

Spin–orbit torque (SOT) technology stands at the forefront of next‐generation non‐volatile memory and logic computing, promising superior endurance and ultrafast dynamics compared to conventional spin‐transfer torque (STT) architectures. However, the persistent requirement of an external magnetic field for deterministic switching of perpendicular magnetization severely impedes high‐density integration and commercial viability. This review systematically evaluates the evolutionary trajectory of symmetry‐breaking strategies developed to overcome this bottleneck. The analysis progresses from early macroscopic structural engineering, such as wedged geometries and lateral asymmetries, to mesoscopic built‐in effective fields driven by interfacial exchange coupling and chiral spin textures. Crucially, we identify a defining paradigm shift in the field: the transition from complex geometric modifications toward intrinsic material‐level innovations, including low‐symmetry crystals, vertical composition gradients (VCG), and synergistic dual‐torque (STT‐SOT) architectures. By resolving the trade‐offs among switching efficiency, thermal stability, and structural complexity, these intrinsic and hybrid approaches offer a practical roadmap for integrating scalable, all‐electrical SOT‐MRAM with standard CMOS back‐end‐of‐line (BEOL) processes. Finally, we establish a dual‐track strategic roadmap: while long‐term breakthroughs require parallel exploration of new exotic physics, we underscore the importance of focusing on mass production and foundry scalability at the current stage.