Giant Ferroelectric Polarization of CaMn7O12 Induced by a Combined Effect of Dzyaloshinskii-Moriya Interaction and Exchange Striction

TL;DR

This paper investigates the origin of giant ferroelectric polarization in CaMn7O12, attributing it to a combined effect of Dzyaloshinskii-Moriya interaction and exchange striction, revealing a novel magnetoelectric coupling mechanism.

Contribution

The study extends a spin-current model and uses density functional calculations to identify the mechanisms behind ferroelectric polarization in CaMn7O12, highlighting the roles of exchange striction and magnetic chirality.

Findings

Giant ferroelectric polarization is caused by symmetric exchange striction.

The polarization magnitude is governed by exchange striction, while its direction is determined by magnetic chirality.

CaMn7O12 exhibits a novel magnetoelectric coupling mechanism.

Abstract

By extending our general spin-current model to non-centrosymmetric spin dimers and performing density functional calculations, we investigate the causes for the helical magnetic order and the origin of the giant ferroelectric polarization of CaMn7O12. The giant ferroelectric polarization is proposed to be caused by the symmetric exchange striction due to the canting of the Mn4+ spin arising from its strong Dzyaloshinskii-Moriya (DM) interaction. Our study suggests that CaMn7O12 may exhibit a novel magnetoelectric coupling mechanism in which the magnitude of the polarization is governed by the exchange striction, but the direction of the polarization by the chirality of the helical magnetic order.