Robust ferroelectric state in multiferroic Mn_1-xZn _xWO₄

We report on the remarkably robust ferroelectric state in the multiferroic compound Mn_1-xZn_xWO₄. Substitution of the magnetic Mn2⊃+ with nonmagnetic Zn2⊃+ reduces the magnetic exchange and provides control of the various magnetic and multiferroic states of MnWO ₄. Only 5% of Zn substitution results in complete suppression of the frustrated collinear (paraelectric) low-temperature phase. The helical magnetic and ferroelectric phase develops as the ground state. The multiferroic state is stable up to a high level of substitution of more than 50%. The magnetic, thermodynamic, and dielectric properties, as well as the ferroelectric polarization of single crystals of Mn_1-xZn_xWO₄, are studied for different substitutions up to x=0.5. The magnetic phases have been identified in single-crystal neutron-scattering experiments. The ferroelectric polarization scales with the neutron intensity of the incommensurate peak of the helical phase.