Electromagnons in multiferroic RMn2O5 compounds and their microscopic   origin
  We summarize the existing experimental data on electromagnons in multiferroic RMn2O5 compounds, where R denotes a rare earth ion, Y or Bi, and discuss a realistic microscopic model of these materials based on assumption that the microscopic mechanism of magnetically-induced ferroelectricity and electromagnon absorption relies entirely on the isotropic Heisenberg exchange and magnetostrictive coupling of spins to a polar lattice mode and does not involve relativistic effects. This model explains many magnetic and optical properties of RMn2O5 manganites, such as the spin re-orientation transition, magnetically-induced polarisation, appearance of the electromagnon peak in the non-collinear spin state and the polarisation of light for which this peak is observed. We compare experimental and theoretical results on electromagnons in RMn2O5 and RMnO3 compounds. 
A. B. Sushkov, M. Mostovoy, R. Valdes Aguilar, S.-W. Cheong and H. D.   Drew