Theory of magnetic field-induced metaelectric critical end point in BiMn$_2$O$_5$

TL;DR

This paper presents a theoretical model for BiMn$_2$O$_5$ that explains the complex phase diagram and critical behavior observed under strong magnetic fields, highlighting the interplay of magnetic and charge degrees of freedom.

Contribution

It introduces a model based on exchange-striction to capture the spin and dipolar interactions in BiMn$_2$O$_5$, reproducing experimental dielectric, magnetic, and polarization behaviors.

Findings

Model reproduces dielectric and magnetic responses

Identifies critical behavior near polarization reversal

Explains proximity to critical end point in phase diagram

Abstract

A recent experiment on the multiferroic BiMn$_2$O$_5$ compound under a strong applied magnetic field revealed a rich phase diagram driven by the coupling of magnetic and charge (dipolar) degrees of freedom. Based on the exchange-striction mechanism, we propose here a theoretical model with the intent to capture the interplay of the spin and dipolar moments in the presence of a magnetic field in BiMn$_2$O$_5$. Experimentally observed behavior of the dielectric constants, magnetic susceptibility, and the polarization is, for the most part, reproduced by our model. The critical behavior observed near the polarization reversal $(P=0)$ point in the phase diagram is interpreted as arising from the proximity to the critical end point.