Magnetization switching by asymmetric topological surfaces

The development of spin-orbit-torque (SOT) devices has sparked considerable research interest, particularly in the quest for novel materials that exhibit high spin-to-charge conversion efficiencies for effective magnetic switching. However, optimizing structure and improving efficiency necessitate theoretical insights and material innovations. In this study, we employ first-principles calculations to investigate the persistent spin current in magnetic topological material MnSb₂Te₄. The weakly asymmetric topological surface states ensure that the spin currents in this system do not cancel out while facilitating high spin-to-charge conversion efficiency through spin-moment locking, thus unprecedentedly enabling SOT switching within a single layer. In experiments, we demonstrate a low critical current density of 7.3 × 10⁵ A/cm² for switching in epitaxial MnSb₂Te₄ thin films, alongside a substantial SOT efficiency of ∼41 at 6 K, consistent with micromagnetic simulations. Additionally, the development of <i>in-situ</i> epitaxial heterostructures of MnSb₂Te₄/FeTe_0.9 allows for the extraction of an exchange-bias-induced effective field, thereby enabling field-free SOT switching within these heterostructures.