Terahertz spectroscopy of spin waves in multiferroic BiFeO$_3$ in high magnetic fields

TL;DR

This study investigates how magnetic modes in BiFeO3 change under high magnetic fields, revealing mode softening, phase transition, and the development of a new mode, supported by a microscopic model that aligns well with experimental data.

Contribution

The paper introduces a microscopic model incorporating Dzyaloshinskii-Moriya interactions and anisotropy that accurately describes magnetic mode behavior in BiFeO3 under high magnetic fields.

Findings

Magnetic modes soften near 18.8 T, indicating a phase transition.

A new strong mode with linear field dependence emerges above the critical field.

The microscopic model successfully explains the experimental spectroscopic observations.

Abstract

We have studied the magnetic field dependence of far-infrared active magnetic modes in a single ferroelectric domain \BFO/ crystal at low temperature. The modes soften close to the critical field of 18.8\,T along the [001] (pseudocubic) axis, where the cycloidal structure changes to the homogeneous canted antiferromagnetic state and a new strong mode with linear field dependence appears that persists at least up to 31\,T. A microscopic model that includes two \DM/ interactions and easy-axis anisotropy describes closely both the zero-field spectroscopic modes as well as their splitting and evolution in a magnetic field. The good agreement of theory with experiment suggests that the proposed model provides the foundation for future technological applications of this multiferroic material.