Giant improper ferroelectricity in the ferroaxial magnet CaMn7O12

TL;DR

This paper reports the discovery of giant improper ferroelectricity in CaMn7O12, induced by a helical magnetic structure and ferroaxial coupling, resulting in the largest magnetically induced polarization measured to date.

Contribution

It demonstrates the largest magnetically induced electric polarization in a multiferroic material, driven by ferroaxial coupling in CaMn7O12.

Findings

2870 μC/m^2 polarization magnitude

Polarization constrained to three-fold rotation axis

Largest magnetically induced polarization recorded

Abstract

In rhombohedral CaMn7O12, an improper ferroelectric polarization of magnitude 2870 {\mu}C m-2 is induced by an incommensurate helical magnetic structure that evolves below TN1 = 90 K. The electric polarization was found to be constrained to the high symmetry three-fold rotation axis of the crystal structure, perpendicular to the in-plane rotation of the magnetic moments. The multiferroicity is explained by the ferroaxial coupling mechanism, which in CaMn7O12 gives rise to the largest magnetically induced, electric polarization measured to date.