title: Oxyhalides: A new class of high-T C multiferroic materials.
abstract: Magnetoelectric multiferroics have attracted enormous attention in the past years because of their high potential for applications in electronic devices, which arises from the intrinsic coupling between magnetic and ferroelectric ordering parameters. The initial finding in TbMnO3 has triggered the search for other multiferroics with higher ordering temperatures and strong magnetoelectric coupling for applications. To date, spin-driven multiferroicity is found mainly in oxides, as well as in a few halogenides. We report multiferroic properties for synthetic melanothallite Cu2OCl2, which is the first discovery of multiferroicity in a transition metal oxyhalide. Measurements of pyrocurrent and the dielectric constant in Cu2OCl2 reveal ferroelectricity below the Néel temperature of ~70 K. Thus, melanothallite belongs to a new class of multiferroic materials with an exceptionally high critical temperature. Powder neutron diffraction measurements reveal an incommensurate magnetic structure below T N, and all magnetic reflections can be indexed with a propagation vector [0.827(7), 0, 0], thus discarding the claimed pyrochlore-like "all-in-all-out" spin structure for Cu2OCl2, and indicating that this transition metal oxyhalide is, indeed, a spin-induced multiferroic material.
authors.affiliation: Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Straße 40, 01187 Dresden, Germany.
authors.forename: Li
authors.initials: L
authors.lastname: Zhao
authors.affiliation: Institut Laue-Langevin, 71 Avenue des Martyrs, F-38042 Grenoble Cedex 9, France.
authors.forename: Maria Teresa
authors.initials: MT
authors.lastname: Fernández-Díaz
authors.affiliation: Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Straße 40, 01187 Dresden, Germany.
authors.forename: Liu Hao
authors.initials: LH
authors.lastname: Tjeng
authors.affiliation: Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Straße 40, 01187 Dresden, Germany.
authors.forename: Alexander C
authors.initials: AC
authors.lastname: Komarek
mesh_terms: D018360:Crystallography, X-Ray; D058085:Iron Compounds / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D008280:Magnetics; D008958:Models, Molecular
chemical_list: D058085:Iron Compounds
keywords: dielectric measurements; ferroelectricity; magnetism; magnetoelectric; multiferroics; neutron scattering; oxyhalide; spin-induced multiferroicity