Multiferroic properties of the antiferroelectric-antiferromagnetic Cu9O2(SeO3)4Cl6

Abstract

The recently experimentally observed multiferroic properties of the antiferroelectric-antiferromagnetic - Cu9O2(SeO3)4Cl6 are studied using a microscopic model and a Green's function technique. The sublattice polarization increases with decreasing temperature and increasing magnetic field h. For the total polarization which is zero without electric field E is observed a double hysteresis loop. The dielectric constant shows two anomalies at the two transition temperatures TN and TE. The magnetodielectric ratio increases with increasing magnetic field below TN. It is shown that a large magnetoelectric coupling g (E=0) or a strong external electric field E (g=const) induces a weak ferromagnetism in this compound. In analogy g (h=0) or an external magnetic field h (g=const) can lead to a weak ferroelectricity.