Melting of incommensurate-ferroelectric phase with magnetic field in multiferroic TbMnO3

We have investigated the reentrant ferroelectric behavior of TbMnO3 under a c-axis-aligned magnetic field (H parallel to c) using neutron and x-ray single-crystal diffraction. We find that below T-N=41 K and at high field the incommensurate ordering of Mn spins melts and coincides with the disappearance of ferroelectricity. The paraelectric phase which emerges is characterized by a simple commensurate antiferomagnetic ordering. We suggest that the reentrance of ferroelectricity at low temperatures and high magnetic field coincides with the development of incommensurate Mn- and Tb-spin ordering.