Theory of multiferroic behavior in cycloidal helimagnets

Abstract

Theories of multiferroic behavior of cycloidal helimagnets are reviewed from the viewpointof the spin current or vector spin chirality. Relativistic spin–orbit interaction leads to thecoupling between the spin current and the electric polarization, and hence the ferroelectricand dielectric responses are a new and important probe for the spin states and theirdynamical properties. Microscopic theories on the ground state polarization for variouselectronic configurations, the collective modes including the electromagnon, and the serioustreatment of classical/quantum fluctuations are discussed with comparison to experimentalresults.