Colossal magnon-phonon coupling in multiferroicEu0.75Y0.25MnO3

We report the spectra of magnetically induced electric dipole absorption in ${\mathrm{Eu}}_{0.75}{\mathrm{Y}}_{0.25}\mathrm{Mn}{\mathrm{O}}_3$ from temperature-dependent far-infrared spectroscopy $(10–250{\mathrm{cm}}^{-1})$. These spectra, which occur only in the $e\Vert a$ polarization, consist of two relatively narrow electromagnon features with onset at $T_{\mathit{FE}}=30\mathrm{K}$ and a broad absorption band that persists to temperatures well above $T_N=47\mathrm{K}$. The observed excitations account for the step up of the static dielectric constant in the ferroelectric phase. The electromagnon at $80{\mathrm{cm}}^{-1}$ 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.