Spin current symmetries generated by GdFeCo ferrimagnet across its magnetisation compensation temperature

TL;DR

This study investigates how spin current symmetries in GdFeCo ferrimagnets behave across the magnetisation compensation temperature, revealing distinct contributions from different electronic subsystems and their implications for spin transport.

Contribution

It provides new insights into the sublattice-specific origins of spin currents in ferrimagnets and how their symmetries are preserved across the compensation point.

Findings

Both SHE and SAHE torques retain their sign across the compensation temperature.

SAHE originates from FeCo 3d electrons, while SHE comes from Gd 5d electrons.

SHE sign remains insensitive to the magnetisation state.

Abstract

Ferrimagnets, composed of antiferromagnetically coupled magnetic sublattices whose net magnetisation can be tuned by temperature, offer a unique platform for probing the symmetry of the spin currents they generate and for identifying the sublattice contributions to these currents. Here, we investigate the spin current symmetries produced by GdFeCo ferrimagnet at a fixed concentration and across a broad temperature range, including the magnetisation compensation point. Using complementary techniques based on spin-torque ferromagnetic resonance spectroscopy, we separate the contributions of the spin Hall effect (SHE) and the spin anomalous Hall effect (SAHE). We show that the torques arising from both mechanisms retain their sign across the magnetisation compensation temperature, and that the SAHE-driven damping-like torque has the opposite sign to the SHE-driven term. We suggest that both effects originates from distinct electronic subsystems: the SHE emerging from Gd 5d electrons, and the SAHE from FeCo 3d electrons. Consequently, the SHE sign remains insensitive to the magnetisation state, whereas the SAHE sign does not invert at compensation, reproducing our observations. Together, these insights clarify the interplay between sublattices in ferrimagnetic spin transport and highlight the potential of ferrimagnetic spin currents to generate spin torques in adjacent layers or within the ferrimagnet itself.