Field-Free, Deterministic Giant Spin-Orbit Torque Switching of 1.3 T Perpendicular Magnetization With Symmetry-Lifted Topological Surface States.

Abstract

The field-free control of perpendicular magnetization using spin-orbit torque (SOT) is a key challenge in spintronics, simplifying design and integration for both memory and logic applications. Unlike conventional heavy metal/ferromagnet heterostructures that already break out-of-plane symmetry, thus can readily offer in-plane switching, realizing deterministic out-of-plane switching requires breaking additional in-plane symmetries. In this study, we demonstrate field-free switching in a heterostructure composed of a self-intercalated 2D magnet, Cr₃Te₄, and a topological insulator, (Bi_0.75Sb_0.25)₂Te₃. In this system, the surface states of the topological insulator ensure efficient charge-to-spin conversion, but not deterministic on its own. The ordered 2 × 1 self-intercalation of the perpendicular magnet provides additional symmetry breaking on the interface, rendering a combined unidirectional m (C_s) symmetry. This synergy allows for extremely strong, field-free SOT switching of Cr₃Te₄ with perpendicular coercivity ≈1.3 T. Unlike exfoliated 2D materials that tend to be single-crystal, our wafer-scale deposition naturally nucleates three equivalent types of 2 × 1 sublattices, and therefore the combined SOT switching manifests an apparent three-fold angular dependence. These findings highlight a promising pathway toward efficient, topological insulator-based spintronic device and material engineering.