Control of spin-orbit torques by interface engineering in topological insulator heterostructures

TL;DR

This paper investigates how interface engineering in topological insulator heterostructures influences spin-orbit torques, revealing that reducing intermixing enhances SOTs and introduces a dominant field-like torque component.

Contribution

It demonstrates that interface chemical control and insertion of a normal metal spacer significantly modify spin-orbit torques in TI/FM heterostructures, highlighting the role of intermixing and surface states.

Findings

Intermixing at the interface critically affects SOT generation.

Insertion of a normal metal spacer improves TI interface properties.

Enhanced field-like torque surpasses Oersted-field torque due to surface spin effects.

Abstract

(Bi$_{1-x}$Sb$_x$)$_2$Te$_3$ topological insulators (TIs) are gathering increasing attention owing to their large charge-to-spin conversion efficiency and the ensuing spin-orbit torques (SOTs) that can be used to manipulate the magnetization of a ferromagnet (FM). The origin of the torques, however, remains elusive, while the implications of hybridized states and the strong material intermixing at the TI/FM interface are essentially unexplored. By combining interface chemical analysis and spin-transfer ferromagnetic resonance (ST-FMR) measurements, we demonstrate that intermixing plays a critical role in the generation of SOTs. By inserting a suitable normal metal spacer, material intermixing is reduced and the TI properties at the interface are largely improved, resulting in strong variations in the nature of the SOTs. A dramatic enhancement of a field-like torque, opposing and surpassing the Oersted-field torque, is observed, which can be attributed to the non-equilibrium spin density in Rashba-split surface bands and to the suppression of spin memory loss.