Magnon and electromagnon excitations in multiferroic DyFe O 3

The existence of electric dipole active magnetic excitations, or electromagnons, in rare-earth orthoferrites was theoretically predicted more than two decades ago but their experimental observation has not been confirmed until now. In this work, magnetic modes in DyFeO${}_{3}$ single crystals were studied at low temperatures and in external magnetic fields ($H$) by means of synchrotron radiation-based far-infrared spectroscopy. The authors report observation of two electromagnons, which appear in the spectra at 20 cm${}^{-1}$ and 50 cm${}^{-1}$ only below the magnetic ordering temperature ${T}_{N}$ of Dy${}^{3+}$ of 4.2 K. It is demonstrated that electromagnons provide a significant contribution to the static electric permittivity along the $c$ axis ${\ensuremath{\epsilon}}_{c}$(0). Both the frequency of the electromagnons and ${\ensuremath{\epsilon}}_{c}$(0,$H$) manifest a strong hysteresis upon cycling of the external magnetic field.