Role of dimensional crossover on spin-orbit torque efficiency in magnetic insulator thin films

TL;DR

This study reveals how the efficiency of spin-orbit torques in magnetic insulator thin films depends on their thickness, showing a transition from 2D to 3D magnetic phases and enhanced SOT efficiency with increasing thickness, enabling low-power spintronic applications.

Contribution

It systematically investigates the impact of magnetic insulator thickness on SOT efficiency, highlighting the role of dimensional crossover and thermal fluctuations in spintronic device performance.

Findings

SOT efficiency increases with film thickness.

Magnetic phase transitions from 2D to 3D occur as thickness increases.

Current-induced SOT switching demonstrated up to 15 nm thickness.

Abstract

Magnetic insulators (MIs) attract tremendous interest for spintronic applications due to low Gilbert damping and absence of Ohmic loss. Magnetic order of MIs can be manipulated and even switched by spin-orbit torques (SOTs) generated through spin Hall effect and Rashba-Edelstein effect in heavy metal/MI bilayers. SOTs on MIs are more intriguing than magnetic metals since SOTs cannot be transferred to MIs through direct injection of electron spins. Understanding of SOTs on MIs remains elusive, especially how SOTs scale with the film thickness. Here, we observe the critical role of dimensionality on the SOT efficiency by systematically studying the MI layer thickness dependent SOT efficiency in tungsten/thulium iron garnet (W/TmIG) bilayers. We first show that the TmIG thin film evolves from two-dimensional to three-dimensional magnetic phase transitions as the thickness increases, due to the suppression of long-wavelength thermal fluctuation. Then, we report the significant enhancement of the measured SOT efficiency as the thickness increases. We attribute this effect to the increase of the magnetic moment density in concert with the suppression of thermal fluctuations. At last, we demonstrate the current-induced SOT switching in the W/TmIG bilayers with a TmIG thickness up to 15 nm. The switching current density is comparable with those of heavy metal/ferromagnetic metal cases. Our findings shed light on the understanding of SOTs in MIs, which is important for the future development of ultrathin MI-based low-power spintronics.