Magnetic resonances of multiferroic TbFe$_3$(BO$_3$)$_4$

TL;DR

This study investigates the low-energy magnetic excitations of the multiferroic compound TbFe$_3$(BO$_3$)$_4$ using high-field infrared spectroscopy and a mean-field spin model, revealing complex magnetic interactions and a six-sublattice ground state.

Contribution

The paper provides a comprehensive magnetic interaction model for TbFe$_3$(BO$_3$)$_4$, including exchange interactions, anisotropy, and g-factors, with improved agreement to experimental data.

Findings

Determined magnetic interactions and g-factors for TbFe$_3$(BO$_3$)$_4$.

Revealed a complex six-sublattice magnetic ground state.

Observed additional high-energy magnetic resonance lines.

Abstract

Low-energy magnetic excitations of the easy-axis antiferromagnet TbFe$_3$(BO$_3$)$_4$ are investigated by far-infrared absorption and reflection spectroscopy in high magnetic fields up to 30 T. The observed field dependence of the resonance frequencies and the magnetization are reproduced by a mean-field spin model for magnetic fields applied both along and perpendicular to the easy axis. Based on this model we determined the full set of magnetic interactions, including Fe-Fe and Fe-Tb exchange interactions, single-ion anisotropy for Tb ions and $g$-factors, which describe the ground-state spin texture and the low-energy spin excitations of TbFe$_3$(BO$_3$)$_4$. Compared to earlier studies we allow a small canting of the nearly Ising-like Tb moments to achieve a quantitative agreement with the magnetic susceptibility measurements. The additional high energy magnetic resonance lines observed, besides the two resonances expected for a two-sublattice antiferromagnet, suggest a more complex six-sublattice magnetic ground state for TbFe$_3$(BO$_3$)$_4$.