Flop of Electric Polarization Driven by the Flop of the Mn Spin Cycloid in Multiferroic TbMnO3

Using in-field single-crystal neutron diffraction, we have determined the magnetic structure of TbMnO3 in the high field P parallel to a phase. We unambiguously establish that the ferroelectric polarization arises from a cycloidal Mn spin ordering, with spins rotating in the ab plane. Our results demonstrate directly that the flop of the ferroelectric polarization in TbMnO3 with applied magnetic field is caused from the flop of the Mn cycloidal plane.