Leveraging symmetry for an accurate spin-orbit torques characterization in ferrimagnetic insulators

TL;DR

This paper presents a new harmonic Hall voltage method combined with macrospin simulations to accurately measure spin-orbit torques in ferrimagnetic insulator heterostructures, overcoming previous experimental challenges.

Contribution

The authors introduce a simple, effective methodology for separating and quantifying damping-like and field-like SOTs and thermoelectric effects in MI-based systems.

Findings

Precise SOT values obtained in Bi-doped YIG/Pt heterostructures.

Joule heating impacts spin transparency and reduces SOTs.

Method enhances understanding of charge-spin interactions in magnetic insulators.

Abstract

Spin-orbit torques (SOTs) have emerged as an efficient means to electrically control the magnetization in ferromagnetic heterostructures. Lately, an increasing attention has been devoted to SOTs in heavy metal (HM)/magnetic insulator (MI) bilayers owing to their tunable magnetic properties and insulating nature. Quantitative characterization of SOTs in HM/MI heterostructures are, thus, vital for fundamental understanding of charge-spin interrelations and designing novel devices. However, the accurate determination of SOTs in MIs have been limited so far due to small electrical signal outputs and dominant spurious thermoelectric effects caused by Joule heating. Here, we report a simple methodology based on harmonic Hall voltage detection and macrospin simulations to accurately quantify the damping-like and field-like SOTs, and thermoelectric contributions separately in MI-based systems. Experiments on the archetypical Bi-doped YIG/Pt heterostructure using the developed method yield precise values for the field-like and damping-like SOTs, reaching -0.14 and -0.15 mT per 1.7x$10^{ 11}$ A/$m^2$, respectively. We further reveal that current-induced Joule heating changes the spin transparency at the interface, reducing the spin Hall magnetoresistance and damping-like SOT, simultaneously. These results and the devised method can be beneficial for fundamental understanding of SOTs in MI-based heterostructures and designing new devices where accurate knowledge of SOTs is necessary.