Magnon and electromagnon excitations in multiferroic DyFeO3

Optical properties of orthorhombic DyFeO3 single crystals have been studied in the far-infrared spectral range of 11-120 cm(-1) at temperatures between 1.5 and 50 K and in magnetic fields up to 7 T. The temperature and magnetic-field dependencies of the antiferromagnetic (AFM) resonance spectra have been measured below and above the AFM ordering temperature of Dy3+ moments with T-N(Dy) = 4.2 K. Hardening of the quasiferromagnetic mode frequency of the AFM resonance due to ordering of Dy3+ moments is observed. Below T-N(Dy) two electric dipole-active magnetic excitations, or electromagnons, appear in the spectra at similar to 20 and similar to 50 cm(-1). The electromagnons vanish with the application of a strong magnetic field along the a or b axis which changes the magnetic structures of Fe3+ and Dy3+ moments into the ones compatible with the spatial inversion symmetry. We show that the electromagnon at similar to 20 cm(-1) provides a significant contribution to the static electric permittivity epsilon. The energies of the electromagnons as well as static electric permittivity manifest a strong hysteresis upon cycling of an external magnetic field at T < T-N(Dy).