Coupling of Magnetic Order, Ferroelectricity, and Lattice Strain in Multiferroic Rare Earth Manganites

Abstract

Multiferroic rare earth manganites attracted recent attention because of the coexistence of different types of magnetic and ferroelectric orders resulting in complex phase diagrams and a wealth of physical phenomena. The coupling and mutual interference of the different orders and the large magnetoelectric effect observed in several compounds are of fundamental interest and bear the potential for future applications in which the dielectric (magnetic) properties can be modified by the onset of a magnetic (dielectric) transition or the application of a magnetic (electric) field. The physical mechanisms of the magnetoelectric effect and the origin of ferroelectric order at magnetic transitions have yet to be explored. We discuss multiferroic phenomena in the hexagonal HoMnO 3 and show that the strong magneto-dielectric coupling is intimately related to the lattice strain induced by unusually large spin-phonon correlations.

Enhancement of magnetodielectric coupling in 6H-perovskites Ba3RRu2O9 for heavier rare-earth cations ( R=Ho<

“…Such a dominant effect of higher order coupling term below magnetic ordering is demonstrated in the hexagonal multiferroic RMnO3. 10,11 One cannot rule out the small effect of magneto-striction, due to a change in lattice parameter (artifact of geometrical effect of a capacitor). However, this effect cannot be solely responsible for a large MD coupling (say, for Ho-member) since such a huge change in lattice parameter is unlikely (no structural change is observed at the onset of magnetic ordering).…”

“…The ferroelectricity in the hexagonal HoMnO3 oxide arises as a result of displacements of Ho-ions and a possible tilting of MnO5 polyhedra, and the magnetic structure is not directly involved to create ferroelectricity. 10,11 The MD coupling in this hexagonal system originates from magnetoelastic coupling, where magneto-striction plays an important role. RMn2O5 oxides constitute a second example of multiferroic materials, whose magnetoelectric properties are governed by 3d-4f electron interactions.…”