New iron-based multiferroics with improper ferroelectricity

TL;DR

This paper reviews recent theoretical and experimental developments in iron-based multiferroics with improper ferroelectricity, highlighting their diverse mechanisms, unique properties, and potential applications in magnetoelectric devices.

Contribution

It introduces a variety of iron-based improper multiferroics, emphasizing their multiple ferroelectric mechanisms and distinctive magnetoelectric properties compared to Mn-based counterparts.

Findings

Multiple improper ferroelectric mechanisms identified

Iron's 3d orbitals enhance magnetoelectric properties

Potential for broader applications in functional materials

Abstract

In this contribution to the special issue on magnetoelectrics and their applications, we focus on some single phase multiferroics theoretically predicted and/or experimentally discovered by the authors in recent years. In these materials, iron is the common core element. However, these materials are conceptually different from the mostly-studied BiFeO$_3$, since their ferroelectricity is improper. Our reviewed materials are not simply repeating one magnetoelectric mechanism, but cover multiple branches of improper ferroelectricity, including the magnetism-driven ferroelectrics, geometric ferroelectric, as well as electronic ferroelectric driven by charge ordering. In this sense, these iron-based improper ferroelectrics can be an encyclopaedic playground to explore the comprehensive physics of multiferroics and magnetoelectricity. Furthermore, the unique characteristics of iron's $3d$ orbitals make some of their magnetoelectric properties quite prominent, comparing with the extensively-studied Mn-based improper multiferroics. In addition, these materials establish the crossover between multiferroics and other fields of functional materials, which enlarges the application scope of multiferroics.