Colossal magnon-phonon coupling in multiferroic Eu${}_{0.75}$Y${}_{0.25}$MnO${}_3$

Abstract

We report the spectra of magnetically induced electric dipole absorption in Eu${}_{0.75}$Y${}_{0.25}$MnO${}_3$ 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 that 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.

4 pages, 3 figures