Temperature dependence of the damping parameter in the ferrimagnet Gd$_3$Fe$_5$O$_{12}$

TL;DR

This study compares two definitions of the damping parameter in ferrimagnets, showing that the newer definition remains stable across temperatures, unlike the conventional one which diverges at the angular momentum compensation point.

Contribution

It demonstrates that the alternative damping parameter ${eta}_{ ext{FiM}}$ remains finite and stable across temperature variations, resolving divergence issues of the conventional parameter in ferrimagnets.

Findings

${eta}_{ ext{FiM}}$ shows no divergence at the compensation temperature.

Conventional ${eta}_{ ext{FM}}$ diverges at the compensation point.

The new damping parameter is less temperature-dependent.

Abstract

The damping parameter ${\alpha}_{\text{FM}}$ in ferrimagnets defined according to the conventional practice for ferromagnets is known to be strongly temperature dependent and diverge at the angular momentum compensation temperature, where the net angular momentum vanishes. However, recent theoretical and experimental developments on ferrimagnetic metals suggest that the damping parameter can be defined in such a way, which we denote by ${\alpha}_{\text{FiM}}$, that it is free of the diverging anomaly at the angular momentum compensation point and is little dependent on temperature. To further understand the temperature dependence of the damping parameter in ferrimagnets, we analyze several data sets from literature for a ferrimagnetic insulator, gadolinium iron garnet, by using the two different definitions of the damping parameter. Using two methods to estimate the individual sublattice magnetizations, which yield results consistent with each other, we found that in all the used data sets, the damping parameter ${\alpha}_{\text{FiM}}$ does not increase at the angular compensation temperature and shows no anomaly whereas the conventionally defined ${\alpha}_{\text{FM}}$ is strongly dependent on the temperature.