Electromagnons in multiferroic RMn$_{2}$O$_{5}$ compounds

Electromagnons, or magnons with electric dipole activity, were observed so far only in some multiferroic RMnO$_{3}$ and RMn$_{2}$O$_{5}$ compounds. Electromagnons in these two systems have essentially different properties. We try to take a systematic look at electromagnons in the whole RMn$_{2}$O$_{5}$ family. In this talk, we report the results of detailed infrared study$^{\ast }$ of YMn$_{2}$O$_{5}$ and TbMn$_{2}$O$_{5 }$ as well as some results on other RMn$_{2}$O$_{5}$ compounds. We found that electromagnons in the RMn$_{2}$O$_{5}$ family is a property of the manganese sublattices. The electromagnon spectrum consists of a set of well defined far infrared (3-80 cm$^{-1})$ modes which are just slightly broader than uncoupled magnons. No obvious changes in the phonon spectrum have been observed. Polarization of electromagnons is in agreement with the dominating symmetric exchange. * A. B. Sushkov, R. Valdes Aguilar, S. Park, S-W. Cheong, and H. D. Drew, cond-mat/ 0608707.