Bulk magnetoelectricity in the hexagonal manganites and ferrites

TL;DR

This paper demonstrates how trimerization in hexagonal manganites and ferrites induces bulk magnetization and magnetoelectric effects, revealing a new type of bulk ME vortex structure through combined theoretical methods.

Contribution

It shows that trimerization induces not only polarization but also bulk magnetization and ME effects, introducing a novel bulk ME vortex concept.

Findings

Prediction of bulk ME vortex structure in RMnO$_3$

Identification of similar phenomena in RFeO$_3$ ferrites

Proposal to measure ME vortex under large magnetic fields

Abstract

Improper ferroelectricity (trimerization) in the hexagonal manganites RMnO$_3$ leads to a network of coupled structural and magnetic vortices that induce domain wall magnetoelectricity and magnetization neither of which, however, occurs in the bulk. Here we combined first-principles calculations, group-theoretic techniques, and microscopic spin models to show how the trimerization not only induces a polarization but also a bulk magnetization and bulk magnetoelectric (ME) effect. This results in the existence of a bulk linear ME vortex structure or a bulk ME coupling such that if direction of polarization reverses so does magnetization. To measure the predicted ME vortex, we suggest RMnO$_3$ under large magnetic field. We suggest a family of materials, the hexagonal RFeO$_3$ ferrites, also display the predicted phenomena in their ground state.