Dielectric loss due to soft domain-wall localized electromagnons in cycloidal magnets

Competing magnetic exchange interactions often result in noncollinear magnetic states, such as spin spirals, which break the inversion symmetry and induce ferroelectric polarization. The resulting strong interactions between spins and ferroelectric polarization give rise to electromagnons and open the door to a technologically important possibility to control magnetic order by electric fields. Here we study the effects of chiral domain walls on dielectric and magnetoelectric properties of cycloidal spirals. We use a quasi-1D model Hamiltonian with competing Heisenberg exchange interactions, leading to a spin spiral, and Dzyaloshinskii-Moriya interactions, responsible for magneto-electric coupling. The results suggest that low frequency dielectric anomalies in spiral magnets, such as TbMnO$_3$ and MnWO$_4$, may originate from hybrid magnon-polar phonon excitations associated with domain walls.