High-Tc ferrolectricity emerging from magnetic degeneracy in cupric oxide

TL;DR

This study reveals a high-temperature multiferroic phase in cupric oxide driven by magnetic degeneracy, where non-magnetic impurities can enhance ferroelectricity through a novel mechanism involving Dzyaloshinskii Moriya interactions.

Contribution

The paper introduces a new mechanism for high-T multiferroicity in cupric oxide based on magnetic degeneracy and impurity effects, supported by density functional and Monte Carlo simulations.

Findings

High-T magnetic phase is ferroelectric with polarization matching experiments.

Non-collinearity and inversion symmetry breaking are stabilized by Dzyaloshinskii Moriya interactions.

Non-magnetic impurities enhance the multiferroic effect.

Abstract

Cupric oxide is multiferroic at unusual high temperatures. From density functional calculations we find that the low-T magnetic phase is paraelectric and the higher-T one ferroelectric, with a size and direction of polarization in good agreement with experiment. By mapping of the ab initio results on an effective spin model we find with Monte Carlo that in the high-T magnetic state non-collinearity and inversion symmetry breaking stabilize each other via the Dzyaloshinskii Moriya interaction. This leads to a novel mechanism for multiferroicity, with the particular property that non-magnetic impurities enhance the effect.