Dynamic magnetoelectric phenomena with electromagnons in rare-earth borate multiferroics

Abstract

Electroactive spin excitations (electromagnons), an analog of the low-frequency quasiferromagnetic antiferromagnetic resonance (AFMR) mode in Fe subsystem, are observed in multiferroic rare-earth ferroborates [specifically in SmFe(BO)] in the frequency range of 40–150 GHz, which are shown to contribute dominantly to the giant static (quasistatic) magnetodielectric effect and which produce two types of dynamic magnetoelectric effects: (a) giant optical activity, which occurs for the wave vector k parallel to the crystallographic -axis, , in a transverse magnetic field and is accompanied by polarization-plane rotation by more than 70 deg mm in the resonance, and (b) directional birefringence and dichroism in a transverse magnetic field -axis, which show up in transmission asymmetry between the forward () and backward () directions, being equivalent to the sign change of the magnetic field, . A theory is developed which explains the observed dynamic magnetoelectric phenomena quantitatively by taking into consideration different symmetries of the tensors of magnetic, magnetoelectric and dielectric susceptibilities for and .