Chiral order and multiferroic domain relaxation in NaFeGe2O6

The magnetic structure and the multiferroic relaxation dynamics of NaFeGe2O6 were studied by neutron scattering on single crystals partially utilizing polarization analysis. In addition to the previously reported transitions, the incommensurate spiral ordering of Fe3+ moments in the ac plane develops an additional component along the crystallographic b direction below T approximate to 5 K, which coincides with a lock-in of the incommensurate modulation. The quasistatic control of the spin-spiral handedness, respectively of the vector chirality, by external electric fields proves the invertibility of multiferroic domains down to the lowest temperature. Time-resolved measurements of the multiferroic domain inversion in NaFeGe2O6 reveal a simple temperature and electric-field dependence of the multiferroic relaxation that is well described by a combined Arrhenius-Merz relation, as it has been observed for TbMnO3. The maximum speed of domain wall motion is comparable to the spin-wave velocity deduced from an analysis of the magnon dispersion.