Magnetically driven ferroelectric order in Ni$_3$V$_2$O$_8$

TL;DR

This study demonstrates that Ni$_3$V$_2$O$_8$ exhibits simultaneous ferroelectric and magnetic ordering during a single phase transition, with strong coupling between these orders influenced by temperature and magnetic field.

Contribution

The paper reveals the coexistence of ferroelectric and magnetic orders in Ni$_3$V$_2$O$_8$ and develops a Landau theory-based model explaining their coupling and polarization direction.

Findings

Ferroelectric and magnetic orders appear simultaneously in Ni$_3$V$_2$O$_8$.

Polarization is restricted to the crystal b axis.

Polarization magnitude is proportional to magnetic order parameter.

Abstract

We show that for Ni$_3$V$_2$O$_8$ long-range ferroelectric and incommensurate magnetic order appear simultaneously in a single phase transition. The temperature and magnetic field dependence of the spontaneous polarization show a strong coupling between magnetic and ferroelectric orders. We determine the magnetic symmetry of this system by constraining the data to be consistent with Landau theory for continuous phase transitions. This phenomenological theory explains our observation the spontaneous polarization is restricted to lie along the crystal b axis and predicts that the magnitude should be proportional to a magnetic order parameter.