Research Summary: Recent studies on magneto-transport properties of topological insulators

(TIs) have attracted great attention due to the rich spin-orbit physics and promising applications

in spintronic devices. Particularly, the strongly spin-momentum coupled electronic states have

been extensively pursued to realize efficient spin-orbit torque (SOT) switching (Figure 1(a)).

However, so far current-induced magnetic switching with TIs has only been observed at

cryogenic temperatures. The goal of this seed project is to understand whether the topologically

protected electronic states in TIs could benefit spintronic applications at room temperature.

In this seed project, full SOT switching has been demonstrated in a TI/ferromagnet

heterostructure with perpendicular magnetic anisotropy (PMA) at room temperature (Figure

1(b)) [1]. Ferrimagnetic cobalt-terbium (CoTb) alloy with bulk PMA was used to overcome the

effects of the interfacial lattice mismatch, permitting direct growth on the classical TI material

Bi2Se3. The low switching current density (~ 3 × 106 A/cm2) provides definitive proof of the high

SOT efficiency from the TI. The SOT efficiency was measured by the current-induced shift of

the Hall resistance-versus-magnetic field hysteresis loops (Figure 1(c)), which is consistent with

the model of the current-induced Néel-type domain wall motion. Accordingly, the effective spin

Hall angle of the TI was determined to be several times larger than in commonly used heavy

metals (Figure 1(c)). Moreover, power consumption for switching a ferromagnetic layer with

either a TI or a heavy metal was calculated, indicating that magnetization switching with TIs

presents much higher energy efficiency than with conventional heavy metals. These results

demonstrate the robustness of TIs as an SOT switching material and provide an avenue

towards applicable TI-based spintronic devices.