Magnetic excitations in the weakly coupled spin dimers and chains material Cu2Fe2Ge4O13 -: art. no. 094434

Magnetic excitations in a weakly coupled spin dimers and chains compound Cu2Fe2Ge4O13 are measured by inelastic neutron scattering. Both structure factors and dispersion of low-energy excitations up to 10 meV energy transfer are well described by a semiclassical spin wave theory involving interacting Fe3+(S=5/2) chains. Additional dispersionless excitations are observed at higher energies, at h omega=24 meV, and associated with singlet-triplet transitions within Cu2+ dimers. Both types of excitations can be understood by treating weak interactions between the Cu2+ and Fe3+ subsystems at the level of the mean-field random phase approximation. However, this simple model fails to account for the measured temperature dependence of the 24 meV mode.