Dynamics of Multiferroic Domain Wall in Spin-Cycloidal FerroelectricDyMnO3

We report the dielectric dispersion of the giant magnetocapacitance (GMC) in multiferroic ${\mathrm{DyMnO}}_3$ over a wide frequency range. The GMC is found to be attributable not to the softened electromagnon but to the electric-field-driven motion of multiferroic domain wall (DW). In contrast to conventional ferroelectric DWs, the present multiferroic DW motion holds an extremely high relaxation rate of $\sim {10}^7{\mathrm{s}}^{-1}$ even at low temperatures. This mobile nature as well as the model simulation suggests that the multiferroic DW is not atomically thin as in ferroelectrics but thick, reflecting its magnetic origin.