Effect of Inversion Symmetry on the Incommensurate Order in Multiferoic RMn2O5 (R = Rare Earth)

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. Disciplines Physical Sciences and Mathematics | Physics Comments Suggested Citation: A.B. Harris, M. Kenzelmann, A. Aharony and O. Entin-Wohlman. (2008). "Effect of inversion symmetry on the incommensurate order in multiferroic RMn2O5 (R = Rare Earth)." Physical Review B. 78, 014407. This journal article is available at ScholarlyCommons: http://repository.upenn.edu/physics_papers/107 Effect of inversion symmetry on the incommensurate order in multiferroic RMn2O5 (R=rare earth) A. B. Harris,1 M. Kenzelmann,2 Amnon Aharony,3 and O. Entin-Wohlman3 1Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA 2Laboratory for Solid State Physics, ETH Zurich, CH-8093 Zurich, Switzerland and Laboratory for Neutron Scattering, ETH & PSI, CH-5232 Villigen PSI, Switzerland 3Department of Physics and the Ilse Katz Center for Mesoand Nano-Scale Science and Technology, Ben Gurion University, Beer Sheva 84105, Israel Received 10 April 2008; published 3 July 2008 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. DOI: 10.1103/PhysRevB.78.014407 PACS number s : 75.25. z, 75.10.Jm, 75.40.Gb