Magnetic field induced phase transitions and phase diagrams of multiferroic Mn0.95Co0.05WO4 with cycloidal spin structure

Abstract

Slightly Co-doped ${\mathrm{MnWO}}_{4}$ at the lowest 5% Co concentration, for which the multiferroic cycloidal phase becomes a ground state, has been studied in magnetic fields up to 60 T by bulk magnetic and electric polarization measurements along different crystallographic directions. The field induced magnetic transitions up to 12 T and the ways they proceed were tracked also by single-crystal neutron diffraction, and the relevant field induced magnetic structures were identified and refined. The complete magnetoelectric phase diagrams for magnetic fields along distinct directions in relation to the cycloidal spin structure have been constructed for magnetic field values exceeding those necessary to induce a spin-flip transition into the paramagnetic state. Their common feature is the existence of nonpolar sinusoidal phases identified by the disappearance of the electric polarization in a field regime slightly below the spin-flip transition. At lower magnetic fields either continuous or abrupt field induced reorientations of the cycloidal magnetic structures were observed, respectively, for a field direction along the crystallographic $b$ axis or along the easy magnetic axis, and the different character of those transitions has been attributed to specific features in the magnetic anisotropy.