Orbital Torque in Rare-Earth Transition-Metal Ferrimagnets

TL;DR

This paper demonstrates that orbital currents in GdyCo100-y ferrimagnetic alloys can generate strong, tunable orbital torques with sign and magnitude controlled by composition and temperature, advancing electrical magnetization control.

Contribution

It reveals that local orbital-to-spin conversion at Gd sites produces significant, tunable orbital torques, with enhanced efficiency at low temperatures due to magnetic ordering.

Findings

Orbital torques are strong and tunable by Gd content and temperature.

Effective spin-orbital Hall angle reaches up to -0.25 in GdyCo100-y/CuOx.

Orbital torque increases at low temperature due to magnetic ordering.

Abstract

Orbital currents have recently emerged as a promising tool to achieve electrical control of the magnetization in thin-film ferromagnets. Efficient orbital-to-spin conversion is required in order to torque the magnetization. Here we show that the injection of an orbital current in a ferrimagnetic GdyCo100-y alloy generates strong orbital torques whose sign and magnitude can be tuned by changing the Gd content and temperature. The effective spin-orbital Hall angle reaches up to -0.25 in a GdyCo100-y/CuOx bilayer compared to +0.03 in Co/CuOx and +0.13 in GdyCo100-y/Pt. This behavior is attributed to the local orbital-to-spin conversion taking place at the Gd sites, which is about five times stronger and of the opposite sign relative to Co. Furthermore, we observe a manyfold increase in the net orbital torque at low temperature, which we attribute to the improved conversion efficiency following the magnetic ordering of the Gd and Co sublattices.