Magnetic excitations in the multiferroic ${\mathrm{Ba}}_2{\mathrm{CoGe}}_2{\mathrm{O}}_7$ are measured by combination of unpolarized and polarized neutron-scattering techniques. The unpolarized neutron spectrum reveals an anisotropic $\mathbf{Q}$ 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 ${\mathrm{Ba}}_2{\mathrm{CoGe}}_2{\mathrm{O}}_7$. The longitudinal fluctuation takes on a main role in the electromagnon mode.

• Received 26 April 2018

DOI:https://doi.org/10.1103/PhysRevB.97.214437