Thermal, dielectric, and magnetic properties in multiferroic Cu_2.85Zn_0.15Mo₂O₉

We study the effects of Zn substitution on single crystals of the low-dimensional multiferroic material Cu₃Mo₂O₉. We report the magnetic field-temperature phase diagram obtained from the temperature and the magnetic field dependences of the specific heat, the dielectric constant, the differential magnetization, and the electric polarization-electric field curve in Cu_2.85Zn_0.15Mo₂O₉. We obtain three phases: a paraelectric and a ferroelectric phase, and a ferroelectric phase with a large coercive electric field. The origin of the last one is discussed based on the charge redistribution effect on a half-filled Mott insulator. In this phase, the Zn substitution induces a robust localized ferroelectric polarization that increases the coercive electric field.