Symmetry and magnetically driven ferroelectricity in rare-earth manganites RMnO3 (R=Gd, Tb, Dy)

TL;DR

This paper explores the symmetry-driven mechanisms behind magnetically induced ferroelectricity in orthorhombic RMnO3 manganites, providing a theoretical framework that explains experimental polarization phenomena under various magnetic conditions.

Contribution

It develops a generalized symmetry-based method to analyze magnetically driven ferroelectricity, including the derivation of Landau-Devonshire functionals and explanation of polarization behaviors in different RMnO3 compounds.

Findings

Ferroelectric polarization in DyMnO3 and TbMnO3 explained by magnetic symmetry.

Magnetic field-induced polarization rotation characterized.

Mechanism of ferroelectric phase stabilization in GdMnO3 identified.

Abstract

This work investigates the magnetically driven ferroelectricity in orthorhombic manganites RMnO3 (R=Gd, Dy or Tb) from the point of view of the symmetry. The method adopted generalizes the one used to characterize the polar properties of displacive modulated structures to the case of an irreducible magnetic order parameter. The symmetry conditions for magnetically induced ferroelectricity are established and the Landau-Devonshire free energy functionals derived from general symmetry considerations. The ferroelectric polarisation observed in DyMnO3 and TbMnO3 at zero magnetic field is explained in terms of the symmetry of a reducible magnetic order parameter. The polarisation rotation induced in these compounds by external magnetic fields and the stabilization of a ferroelectric phase in GdMnO3 are accounted for by a mechanism in which magnetization and polarization are secondary order parameters that are not directly coupled but compete with each other through their coupling to competing primary modulated order parameters.