Magnetic ground state and multiferroicity in BiMnO$_3$

TL;DR

This paper proposes that BiMnO$_3$ has a noncentrosymmetric magnetic ground state with coexisting ferromagnetic and antiferromagnetic orders, leading to multiferroicity, and shows how a strong magnetic field can restore centrosymmetry.

Contribution

It demonstrates that the true symmetry of BiMnO$_3$ is $Cc$, compatible with a noncollinear magnetic ground state, and provides a first-principles based analysis of its multiferroic properties.

Findings

The magnetic ground state breaks centrosymmetry and is noncollinear.

A magnetic field of about 35 Tesla restores centrosymmetry and switches off ferroelectric polarization.

The model's predictions agree well with experimental data for BiCrO$_3$.

Abstract

We argue that the centrosymmetric $C2/c$ symmetry in BiMnO$_3$ is spontaneously broken by antiferromagnetic (AFM) interactions existing in the system. The true symmetry is expected to be $Cc$, which is compatible with the noncollinear magnetic ground state, where the ferromagnetic order along one crystallographic axis coexists with the the hidden AFM order and related to it ferroelectric polarization along two other axes. The $C2/c$ symmetry can be restored by the magnetic field $B \sim 35$ Tesla, which switches off the ferroelectric polarization. Our analysis is based on the solution of the low-energy model constructed for the 3d-bands of BiMnO$_3$, where all the parameters have been derived from the first-principles calculations. Test calculations for isostructural BiCrO$_3$ reveal an excellent agreement with experimental data.