Magnetic and multiferroic phases of single-crystalline Mn_0.85 Co_0.15 WO₄

The magnetic and multiferroic phase diagram of Mn_0.85 Co _0.15 WO₄ single crystals is investigated by means of magnetic, heat-capacity, dielectric, polarization, and neutron-scattering experiments. Three magnetic phase transitions are detected through distinct anomalies in all physical quantities. The ferroelectric polarization is observed only along the b axis below 10 K but not along the a axis as recently suggested. The magnetic phases studied by neutron scattering are very complex. Up to four different magnetic structures, partially coexisting at certain temperature ranges, have been identified. Upon decreasing temperature two commensurate phases (AF4, AF1) are followed by an incommensurate phase (AF5) and a second incommensurate phase (AF2) is detected as a minor phase. The ferroelectric polarization is possibly associated with both (AF2 and AF5) phases.