Colossal magnon-phonon coupling in multiferroic Eu_0.75Y_0.25MnO₃

We report the spectra of magnetically induced electric dipole absorption in Eu_0.75Y_0.25MnO₃ 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 T_FE=30 K and a broad absorption band that persists to temperatures well above T_N=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.