Re-entrant ferroelectricity and the multiferroic phase diagram of Mn1-xFexWO4

We report the discovery of re-entrant ferroelectricity in the phase diagram of multiferroic Fe-substituted MnWO4. At zero magnetic field (H) the spin-spiral ferroelectric (FE) state is completely suppressed at Fe substitutions (x) exceeding 0.04. For x < 0(04 a zero-field ferroelectric phase exists in a narrow temperature (T) range. This phase shows a re-entrant behavior at lower T above a critical magnetic field. The re-entrant FE transition is explored by polarization, dielectric constant, and magnetization measurements. The complete multiferroic x-T-H phase diagram of Mn1-xFexWO4 is derived.