UCLA

Spintronics harnesses spin degrees of freedom for information storage and processing, offering notable advantages of non-volatility, low power consumption, and fast speed. Topology, as invariant geometric and physical properties under continuous deformation, endows spintronics with higher efficiency and robustness against external perturbations. Protected by real-space topology, magnetic skyrmions are swirling topological spin structures with particle-like properties and potential candidates for high-density, non-volatile storages. As an electrical readout of magnetic skyrmions, the topological Hall effect (THE) is a non-monotonic feature in the Hall signal. However, in the presence of an anomalous Hall effect (AHE), the THE can be easily confused with the non-monotonic co-existence of two AHEs, or artifact of “THE”. Here, we develop systematic methodologies for distinguishing between the two. Genuine THE occurs in the transition region of the AHE, while artifact of “THE” may occur well beyond the saturation of the “AHE component”. Minor loops of genuine THE with AHE are always within the full loop, while minor loops of artifact of “THE” may reveal a single loop that cannot fit into the “AHE component”. The temperature or gate dependence of artifact of “THE” may also be accompanied by a polarity change of the “AHE component”. Our methods may help future researchers ascertain genuine THE for applications of magnetic skyrmions. Protected by k-space topology, magnetic topological insulators (MTI) can apply highly efficient spin-orbit torque (SOT) and manipulate the magnetization with their unique topological surface states. Here, we demonstrate 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. A giant switched anomalous Hall resistance of 9.2 kΩ is realized, among the largest of all SOT systems. The SOT switching current density can be reduced to 2.8×105 A/cm2. 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 T/(106 A/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.