Investigating spin and orbital effects via spin-torque ferromagnetic resonance

TL;DR

This paper experimentally investigates spin and orbital torque effects in bilayer systems using spin-torque ferromagnetic resonance, revealing orbital torque contributions linked to the orbital Hall effect and their potential for magnetization switching.

Contribution

It provides the first experimental evidence of orbital torque associated with the orbital Hall effect in bilayer systems, expanding understanding of torque mechanisms.

Findings

Demonstrated damping-like and field-like torque components in bilayers

Identified out-of-plane torque component linked to interfacial effects

Provided evidence of orbital torque driven by the orbital Hall effect

Abstract

In this work, we experimentally investigate spin and orbital torque phenomena using the spin-torque ferromagnetic resonance (ST-FMR) technique in a series of bilayer systems composed of different normal metal (NM) materials. Permalloy (Py) and Ni were employed as ferromagnetic (FM) layers to probe the spin and orbital torque responses, respectively. For the SiO$_2$/FM/NM bilayers, we extracted the damping-like and field-like torque components, as well as the damping-like torque efficiency for each sample, and compared our results with previously reported numerical and experimental data in the literature. Additionally, we experimentally demonstrate the presence of an out-of-plane torque component, which we attribute to interfacial mechanisms and associate with a spin-orbital polarized current along the $z$-direction. This interpretation is supported by the azimuthal angular dependence of the applied magnetic field. Our results provide compelling evidence of orbital torque associated with the orbital Hall effect (OHE) in several materials, thereby broadening the prospects for magnetization switching driven by orbital torque.