Multiferroicity induced by dislocated spin-density waves

TL;DR

This paper introduces a new mechanism where dislocated collinear spin-density waves induce multiferroicity by breaking inversion symmetry locally, explaining observed phenomena and predicting oscillating polarization in certain materials.

Contribution

It reveals a novel pathway for multiferroicity driven by phase dislocations in spin-density waves, independent of magnetic inversion symmetry breaking.

Findings

Dislocated spin-density waves can induce ferroelectricity.

Multiferroic phases can form at magnetic commensurability transitions.

Oscillating electrical polarization is predicted in these multiferroics.

Abstract

We uncover a new pathway towards multiferroicity, showing how magnetism can drive ferroelectricity without relying on inversion symmetry breaking of the magnetic ordering. Our free-energy analysis demonstrates that any commensurate spin-density-wave ordering with a phase dislocation, even if it is collinear, gives rise to an electric polarization. Due to the dislocation the electronic and magnetic and inversion centers do not coincide, which turns out to be a sufficient condition for multiferroic coupling. The novel mechanism explains the formation of multiferroic phases at the magnetic commensurability transitions, such as the ones observed in YMn$_{2}$O$_{5}$ and related compounds. We predict that in these multiferroics an oscillating electrical polarization is concomitant with the uniform polarization. On the basis of our theory we put forward new types of magnetic materials that are potentially ferroelectric.