Electromagnons in multiferroic YMn2O5 and TbMn2O5
  Based on temperature dependent far infrared transmission spectra of YMn2O5 and TbMn2O5 single crystals, we report the observation of electric dipole-active magnetic excitations, or electromagnons, in these multiferroics. Electromagnons are found to be directly responsible for the step-like anomaly of the static dielectric constant at the commensurate--incommensurate magnetic transition and are the origin of the colossal magneto-dielectric effect reported in these multiferroics. 
A. B. Sushkov, R. Valdes Aguilar, S. Park, S-W. Cheong, and H. D. Drew