The Magnetoelastic Distortion of Multiferroic BiFeO$_3$ in the Canted Antiferromagnetic State

TL;DR

This study reveals how magnetoelastic coupling causes monoclinic distortion in BiFeO$_3$'s canted antiferromagnetic state, using THz spectroscopy to refine the spin model with symmetry-violating anisotropy terms.

Contribution

It introduces a revised spin model for BiFeO$_3$ that includes new anisotropy terms induced by magnetoelastic effects, explaining the observed symmetry violation.

Findings

The spin-wave spectrum fits a model with rhombohedral symmetry violation.

Magnetoelastic coupling induces monoclinic distortion in the magnetic state.

New anisotropy terms depend on magnetic field direction.

Abstract

Using THz spectroscopy, we show that the spin-wave spectrum of multiferroic BiFeO$_3$ in its high-field canted antiferromagnetic state is well described by a spin model that violates rhombohedral symmetry. We demonstrate that the monoclinic distortion of the canted antiferromagnetic state is induced by the single-ion magnetoelastic coupling between the lattice and the two nearly anti-parallel spins. The revised spin model for BiFeO$_3$ contains two new single-ion anisotropy terms that violate rhombohedral symmetry and depend on the direction of the magnetic field.