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The interaction of light with electromagnons in a sinusoidally modulated antiferromagnetic phase of TbMnO3 is examined. It is predicted that the frequency dependence of the dielectric tensor εzz changes substantially at the transition from a sinusoidal into a spiral magnetic phase with spontaneous electric polarization. The phason mode of such a transition is an electromagnon mode in which the magnetoelectric phase is due to modulation of the magnetic structure.

A brief review of research performed on ferroelectromagnetic crystals over the 50years following the discovery of these materials by G. A. Smolenskiĭ and his colleagues is given. During the first decades single crystals and solid solutions of ferrloelectromagnetic substances were synthesized and the first evidence of an interaction between the ferroelectric and magnetic subsystems was obtained. The first two colossal magnetoelectric (ME) effects in nickel-iodine boracite were discovered. The theory explained qualitatively the observed and predicted new ME phenomena. Subsequently, the class of ferroelectromagnets grew, and compounds in which the electric polarization was induced by a spiral magnetic structure appeared. Measuring techniques improved. The discovery at the end of the 20th century of a new optical method of second-harmonic generation set the conditions for a new renaissance in ME studies. An entire series of new colossal ME effects attesting to the realization of cross ME control of the electric (magnetic) properties of a crystal by a magnetic (electric) field has now been discovered. The ME effects of greatest significance which have been discovered in the last few years are described. It is noted that ferroelectromagnets with electric polarization of an electronic nature (compounds with mixed valence, semiconductors) are promising materials.