Polarization analysis of magnetic excitation in multiferroic Ba2CoGe2O7

Abstract

Magnetic excitations in the multiferroic Ba2CoGe2O7 are measured by combination of unpolarized and polarized neutron-scattering techniques. The unpolarized neutron spectrum reveals an anisotropic Q dependence of the intensity of the electromagnon mode at 4 meV. The analysis of the polarized neutron spectra identifies the directions of the magnetic fluctuations of the observed modes. The determined modes are consistent with the calculation by the extended spin-wave theory. A couple of transverse modes and a single longitudinal mode are involved in the magnetic excitation of Ba2CoGe2O7. The longitudinal fluctuation takes on a main role in the electromagnon mode.