  Competing magnetic exchange interactions often result in non-collinear
magnetic states, such as spin spirals, which break the inversion symmetry and
induce ferroelectric polarization. The resulting strong interactions between
magnetic and dielectric degrees of freedom lead to a technologically important
possibility to control magnetic order by electric fields and to electromagnons,
magnetic excitations that can be excited by an electric dipole of the
electromagnetic field. Here we study the effects of chiral domain walls on
magnetoelectric properties of spiral magnets. We use a quasi-1D model
Hamiltonian with competing Heisenberg exchange interactions, leading to a spin
spiral, and Dzyaloshinskii-Moriya interactions, that couple spins and electric
dipoles and mix magnon and phonon excitations. The results suggest that low
frequency dielectric anomalies in spiral magnets, such as TbMnO3 and MnWO4, may
originate from hybrid magnon - polar phonon excitations associated with domain
walls.
