Giant Hall Switching by Surface‐State‐Mediated Spin‐Orbit Torque in a Hard Ferromagnetic Topological Insulator

Topological insulators (TI) and magnetic topological insulators (MTI) can apply highly efficient spin‐orbit torque (SOT) and manipulate the magnetization with their unique topological surface states (TSS) with ultrahigh efficiency. Here, efficient SOT switching of a hard MTI, V‐doped (Bi,Sb)2Te3 (VBST), with a large coercive field that can prevent the influence of an external magnetic field, is demonstrated. A giant switched anomalous Hall resistance of 9.2 kΩ is realized, among the largest of all SOT systems, which makes the Hall channel a good readout and eliminates the need to fabricate complicated magnetic tunnel junction (MTJ) structures. The SOT switching current density can be reduced to 2.8 × 105 A cm−2, indicating its high efficiency. Moreover, as the Fermi level is moved away from the Dirac point by both gate and composition tuning, VBST exhibits a transition from edge‐state‐mediated to surface‐state‐mediated transport, thus enhancing the SOT effective field to (1.56 ± 0.12) × 10−6 T A−1 cm2 and the interfacial charge‐to‐spin conversion efficiency to 3.9 ± 0.3 nm−1. The findings establish VBST as an extraordinary candidate for energy‐efficient magnetic memory devices. Highly efficient current‐driven spin‐orbit torque (SOT) switching is observed in a hard ferromagnetic topological insulator (TI), V‐doped (Bi,Sb)2Te3 (VBST), with a record large switched anomalous Hall resistance of 9.2 kΩ by current. The SOT efficiency is significantly enhanced by Fermi level tuning, as VBST exhibits a transition from edge‐state‐mediated to surface‐state‐mediated transport.