Dynamical multiferroicity

In many multiferroic materials, the ferroelectric polarization is induced by a spatially varying magnetization such as a spin spiral. Here the authors introduce the reciprocal effect, in which a time-dependent electric polarization induces a magnetization even in previously nonmagnetic materials. The authors illustrate this dynamical multiferroic effect with four examples---the phonon Zeeman effect, the optical excitation of magnons and electromagnons, and the inverse Faraday effect---which they investigate using a combination of density functional theory, and microscopic and phenomenological analysis. The mechanism provides a general route to dynamically engineering new behaviors that are not accessible in the static domain.