X phase of MnWO4

A long-standing issue, the magnetic structure of the so-called X phase of MnWO4, has been solved by single-crystal neutron diffraction. Emerging from the well-known ferroelectric phase which presents an electric polarization P//b and which is induced by a cycloidal magnetic order called AF2, this phase is reached by application of a magnetic field along the b axis and is characterized by a flop of the electric polarization towards the a axis. We have identified this new phase as a reoriented cycloidal spin structure, AF2', and its evolution from the AF2 phase has been thoroughly described. Unlike for the usual magnetic-field-induced spin-flop transitions, this high-field flopped phase does not directly develop from the low-field phase but emerges via the nonpolar collinear commensurate AF1 phase, which creeps in between. This evolution is in good agreement with the observed field-induced change in Pb and Pa electric polarization as well as with magnetic susceptibility data. © 2014 American Physical Society.