Jia C.L. and Berakdar J.

Both the Dzyaloshiskii?Moriya interaction and the exchange striction are shown to affect dynamically the magnetoelectric excitations in the helical multiferroics. The exchange striction results in a biquadratic interaction between the spins and the transverse phonons, giving rise to quantum fluctuations of the ferroelectric polarization P. This leads to low-lying phonon modes that are perpendicular to P and to the helical spins at small wave vector but are parallel to P at a wave vector close to the magnetic modulation vector. For spin 1/2 helimagnet, the local polarization can be completely reversed by the spin fluctuation, and so does the direction of the on-site spin chirality, which allows for a finite differential scattering intensity of polarized neutrons from a cycloidal magnet.

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