title: Magnetoelectric effects in the spiral magnets CuCl2and CuBr2.
abstract: The nature and symmetry of transition mechanisms in the spin-spiral copper halides CuCl2and CuBr2are analyzed theoretically. The magnetoelectric effects observed in the two multiferroic compounds are described and their phase diagram at zero and applied magnetic fields are worked out. The emergence of the electric polarization at zero field below the paramagnetic phase is shown to result from the coupling of two distinct spin-density waves and to be only partly related to the Dzialoshinskii-Moriya interactions. Applying a magnetic field along the two-fold monoclinic axis of CuCl2yields a decoupling of the spin-density waves modifying the symmetry of the phase and the spin-spiral orientation. The remarkable periodic dependences of the magnetic susceptibility and polarization, on rotating the field in the monoclinic plane, are described theoretically.
authors.affiliation: Laboratoire de Physique des Systèmes Complexes, Université de Picardie, 80000 Amiens, France.
authors.forename: P
authors.initials: P
authors.lastname: Tolédano
authors.forename: A P
authors.initials: AP
authors.lastname: Ayala
authors.forename: A F G
authors.initials: AF
authors.lastname: Furtado Filho
authors.forename: J P C
authors.initials: JP
authors.lastname: do Nascimento
authors.forename: M A S
authors.initials: MA
authors.lastname: Silva
authors.forename: A S B
authors.initials: AS
authors.lastname: Sombra