Spontaneous Polarization Reversal in Multiferroic Mn0.85Co0.15WO4 Induced by an External Magnetic Field

The multiferroic properties of Mn_0.85Co_0.15WO₄ are studied in magnetic fields oriented along the monoclinic c-axis. A spontaneous sign reversal of the ferroelectric polarization is observed upon decreasing temperature if cooled in a constant magnetic field. This unusual phenomenon is explained by the coexistence of different multiferroic phases with conical and spiral spin structures. These phases form domains which contribute to the electrical polarization in different temperature ranges. The sign reversal of the polarization is explained by an analysis of the contributions from the different domains to the net value of the polarization. It is concluded that the spiral and conical magnetic orders in neighboring domains are strongly coupled leading to the preservation of the spin chirality across the domain walls.