# Thickness Dependence of Spin-Orbit Torques in Ferrimagnetic GdFeCo Alloys

## TL;DR

This study investigates how spin-orbit torques in GdFeCo alloys vary with thickness and composition, revealing that effective SOT fields decrease with thickness but switching efficiency remains unaffected, and that the torque diverges at the magnetization compensation point.

## Contribution

It provides the first systematic analysis of thickness dependence of SOT in bulk PMA GdFeCo alloys, showing inverse relation of SOT fields with thickness and composition effects.

## Key findings

- Effective SOT fields decrease inversely with thickness.
- 30nm thick GdFeCo can be switched with SOT.
- Spin torque diverges at the magnetization compensation point.

## Abstract

So far, studies of spin-orbit torques (SOT) in ferromagnets with perpendicular magnetic anisotropy (PMA) have been restricted to ultra thin samples, while a systematic study of its thickness dependence is still lacking in literature. In this article we discuss the thickness dependence of SOT in GdFeCo samples with bulk PMA. We show that the effective SOT fields are decreasing inversely as a function of thickness while the spin-Hall angle stays constant, as expected from angular momentum conservation. Further we show that even 30nm thick GdFeCo samples can be switched with SOT. This has important technological implications as the switching efficiency does not depend on the thickness. Finally, we investigate the composition dependence of SOT in 30nm thick GdFeCo samples and find that the spin torque effective field diverges at the magnetization compensation point.