Colossal magnon-phonon coupling in multiferroic Eu0.75 Y0.25 Mn O3

We report the spectra of magnetically induced electric dipole absorption in Eu0.75 Y0.25 Mn O3 from temperature-dependent far-infrared spectroscopy (10-250 cm-1). These spectra, which occur only in the e a polarization, consist of two relatively narrow electromagnon features with onset at TFE =30 K and a broad absorption band that persists to temperatures well above TN =47 K. The observed excitations account for the step up of the static dielectric constant in the ferroelectric phase. The electromagnon at 80 cm-1 is observed to be strongly coupled to the nearby lowest optical phonon which transfers more than 1/2 of its spectral weight to the magnon. We attribute the origin of the broad background absorption to the two-magnon-emission decay process of the phonon.