Spin dynamics study and experimental realization of tunable single-ion anisotropy in multiferroic Ba2CoGe2O7 under external magnetic fields
We report a spin-wave study on multiferroic Ba2CoGe2O7 under magnetic fields up to 12 T using low-energy inelastic neutron scattering. In-plane transverse (T1) spin-wave modes are highly dispersive along (h 00 ) and rather flat but strong in intensity along (30 l ). In addition, two dispersive electromagnon modes have been observed around 3.5 meV. Dispersion of the out-of-plane transverse modes (T2) under fields reveals that the single-ion anisotropy constant decreases with increasing magnetic field, which is consistent with the linear spin-wave theory. Our results imply that the field-dependent single-ion anisotropy plays a crucial role in determining the characteristics of T2 and electromagnon modes in the three-dimensional anisotropic spin-wave spectrum.