Origin of multiferroicity in MnWO${}_{4}$

Origin of multiferroicity in MnWO $_{4}$

I. V. Solovyev

Phys. Rev. B 87, 144403 – Published 4 April 2013

Abstract

MnWO $_{4}$ is regarded as a canonical example of multiferroic materials, where the multiferroic activity is caused by a spin-spiral alignment. We argue that, in reality, MnWO $_{4}$ has two sources of the spin spirality, which conflict with each other. One source is the Dzyaloshinskii-Moriya (DM) interactions, reflecting the $P 2 / c$ symmetry of the lattice. The $P 2 / c$ structure of MnWO $_{4}$ has an inversion center that connects two Mn sublattices. Therefore, from the viewpoint of DM interactions, different Mn sublattices are expected to have opposite spin chirality. Another source is competing isotropic exchange interactions, which tend to form a spin-spiral texture with the same chirality in both magnetic sublattices. Thus there is a conflict between DM and isotropic exchange interactions, which makes these two sublattices inequivalent and, therefore, breaks the inversion symmetry. Our theoretical analysis is based on the low-energy model, derived from first-principles electronic structure calculations.