Order Parameters and Phase Diagram of Multiferroic RMn$_2$O$_5$

TL;DR

This paper develops a comprehensive magnetic phase diagram for multiferroic RMn$_2$O$_5$ compounds, explaining magnetic and ferroelectric phases through symmetry-based order parameters and proposing experiments to test the theory.

Contribution

It introduces a symmetry-based order parameter framework for the magnetic phases of RMn$_2$O$_5$ and links magnetic order to ferroelectricity via a phenomenological magneto-electric coupling.

Findings

Different magnetic sequences are explained by the phase diagram.

Magnetic phases can also be ferroelectric due to magneto-electric coupling.

Proposed experiments can validate the theoretical model.

Abstract

The generic magnetic phase diagram of multiferroic RMn$_2$O$_5$ (with R=Y, Ho, Tb, Er, Tm), which allows different sequences of ordered magnetic structures for different R's and different control parameters, is described using order parameters which explicitly incorporate the magnetic symmetry. A phenomenological magneto-electric coupling is used to explain why some of these magnetic phases are also ferroelectric. Several new experiments, which can test this theory, are proposed.