Current-nonlinear Hall effect and spin-orbit torque magnetization switching in a magnetic topological insulator

TL;DR

This paper investigates the origins of the second harmonic Hall voltage in magnetic topological insulators, revealing it is mainly due to magnon scattering rather than spin-orbit torque, and demonstrates magnetization switching with high current density.

Contribution

It clarifies the mechanism behind the second harmonic Hall voltage in TI heterostructures, showing it is dominated by magnon scattering, and demonstrates effective SOT-induced magnetization switching.

Findings

Second harmonic Hall voltage is mainly due to magnon scattering, not SOT.

Accurate spin Hall angle estimation is challenging when magnons dominate.

Magnetization switching achieved with current density of ~2.5×10^{10} A/m^2.

Abstract

Precise estimation of spin Hall angle as well as successful maximization of spin-orbit torque (SOT) form a basis of electronic control of magnetic properties with spintronic functionality. Until now, current-nonlinear Hall effect, or second harmonic Hall voltage has been utilized as one of the methods for estimating spin Hall angle, which is attributed to the magnetization oscillation by SOT. Here, we argue the second harmonic Hall voltage in magnetic/nonmagnetic topological insulator (TI) heterostructures, Cr$_x$(Bi$_{1-y}$Sb$_y$)$_{2-x}$Te$_3$/(Bi$_{1-y}$Sb$_y$)$_2$Te$_3$. From the angular, temperature and magnetic field dependence, it is unambiguously shown that the large second harmonic Hall voltage in TI heterostructures is governed not by SOT but mainly by asymmetric magnon scattering mechanism without magnetization oscillation. Thus, this method does not allow an accurate estimation of spin Hall angle when magnons largely contribute to electron scattering. Instead, the SOT contribution in a TI heterostructure is exemplified by current pulse induced non-volatile magnetization switching, which is realized with a current density of $\sim 2.5 \times 10^{10} \mathrm{A/m}^2$, showing its potential as spintronic materials.