Improper Ferroelectricity in Helicoidal Antiferromagnet Cu3Nb2O8

TL;DR

This study investigates the microscopic origin of improper ferroelectricity in Cu3Nb2O8, revealing the role of magnetic correlations and ferro-axial vectors in its multiferroic behavior through comprehensive measurements.

Contribution

It provides a detailed experimental analysis linking magnetic correlations and ferro-axial vectors to improper ferroelectricity in Cu3Nb2O8, clarifying its microscopic mechanism.

Findings

Dielectric constant suppressed by magnetic field without shifting in temperature

Magneto-dielectric effect indicates magnetic correlation contribution

Results support ferro-axial vector mechanism for multiferroicity

Abstract

Cu3Nb2O8 is an unusual multiferroic compound that undergoes a series of magnetic ordering at low temperatures. Concurrent development of electric polarization has been reported at TN1 ~25 K corresponding to a non-collinear helicoidal ordering (Phys. Rev. Lett. 107, 137205 (2011)). But questions remain on the microscopic origin of such phenomena. In this communication, we report a detailed study of induced polar ordering in Cu3Nb2O8 by performing polarization, magnetization, dielectric constant and heat capacity measurements over a broad range of temperature and magnetic field. The dielectric constant shows suppression in the magnetic field but it does not shift to lower temperature with the application of external field. The appearance of magneto-dielectric effect signifies the contribution of q-dependent magnetic correlation function with enhanced weightage in the presence of magnetic field. This magnetic correlation function is associated with the ferro-axial vector and our overall results support this mechanism for the observation of muliferroicity in Cu3Nb2O8.