Effect of Inversion Symmetry on Incommensurate Order in Multiferroic RMn2O5, R=rare earth

TL;DR

This paper investigates how inversion symmetry influences incommensurate magnetic order and magnetoelectric interactions in multiferroic RMn2O5, revealing higher-order effects and relations between different magnetic phases.

Contribution

It introduces a method to include inversion symmetry in the representation analysis of magnetic structures and explores its impact on magnetoelectric coupling in multiferroics.

Findings

Derived relations between spin wave functions of incommensurate and commensurate phases.

Identified higher-order magnetoelectric interactions that can induce spontaneous polarization.

Established transformation properties of order parameters under space group operations.

Abstract

Starting from the irreducible representations of the group of the wave vector we construct the spin wave functions consistent with inversion symmetry, neglected in the usual representation analysis. We obtain the relation between the basis functions of different members of the star of the wave vector. We introduce order parameters and determine their transformation properties under the operations of the space group of the paramagnetic crystal. The results are applied to construct terms in the magnetoelectric interaction which are quadratic and quartic in the magnetic order parameters. The higher order magnetoelectric interactions can in principle induce components of the spontaneous polarization which are not allowed by the lowest order magnetoelectric interaction. We also obtain the relation between the spin wave functions of the incommensurate phase and those of the commensurate phase which lead to analogous relations between the order parameters of these two phases.