title: Landau theory of topological defects in multiferroic hexagonal manganites.
abstract: Topological defects in ordered states with spontaneously broken symmetry often have unusual physical properties, such as fractional electric charge or a quantized magnetic field flux, originating from their non-trivial topology. Coupled topological defects in systems with several coexisting orders give rise to unconventional functionalities, such as the electric-field control of magnetization in multiferroics resulting from the coupling between the ferroelectric and ferromagnetic domain walls. Hexagonal manganites provide an extra degree of freedom: in these materials, both ferroelectricity and magnetism are coupled to an additional, non-ferroelectric structural order parameter. Here we present a theoretical study of topological defects in hexagonal manganites based on Landau theory with parameters determined from first-principles calculations. We explain the observed flip of electric polarization at the boundaries of structural domains, the origin of the observed discrete vortices, and the clamping between ferroelectric and antiferromagnetic domain walls. We show that structural vortices induce magnetic ones and that, consistent with a recent experimental report, ferroelectric domain walls can carry a magnetic moment.
authors.affiliation: 1] Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, 9747 AG, Groningen, The Netherlands [2] Department of Physics and Astronomy, Rutgers University, Piscataway, New Jersey 08854, USA.
authors.forename: Sergey
authors.initials: S
authors.lastname: Artyukhin
authors.affiliation: Materials Research Laboratory, University of California, Santa Barbara, California 93106-5121, USA.
authors.forename: Kris T
authors.initials: KT
authors.lastname: Delaney
authors.affiliation: Materials Theory, ETH Zurich, Wolfgang-Pauli-Strasse 27, CH-8093 Zurich, Switzerland.
authors.forename: Nicola A
authors.initials: NA
authors.lastname: Spaldin
authors.affiliation: Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, 9747 AG, Groningen, The Netherlands.
authors.forename: Maxim
authors.initials: M
authors.lastname: Mostovoy