Unconventional magnetic ferroelectricity in the quadruple perovskite NaMn$_7$O$_{12}$

TL;DR

This study reveals unconventional magnetic ferroelectricity in NaMn7O12, where ferroelectricity arises from symmetric exchange interactions at magnetic domain boundaries, showing promising polarization levels for multiferroic applications.

Contribution

It demonstrates a novel mechanism of ferroelectricity induced by symmetric exchange interactions in a quadruple perovskite, differing from traditional models.

Findings

Ferroelectricity coincides with broadening of magnetic hysteresis loops.

Electric polarization measured is 0.027 μC/cm², relatively large for magnetic multiferroics.

Unconventional behavior linked to domain boundary effects.

Abstract

By means of magnetic, specific heat and pyroelectric measurements, we report on magnetic ferroelectricity in the quadruple perovskite \namno, characterized by a canted antiferromagnetic (AFM) CE structure. Surprisingly, ferroelectricity is concomitant to a dramatic broadening of the magnetic hysteresis loop, well below the AFM ordering temperature. This unconventional behavior shows that the formation of ferroelectric domains is induced by the symmetric exchange interaction in the local scale, e.g. at magnetic domain boundaries or defects. The value of electric polarization, $P = 0.027 \mu$C cm$^{-2}$, measured in polycrystalline samples is comparatively large as compared to other magnetic multiferroics, suggesting that the above scenario is promising indeed for the rational design of practical multiferroic materials.