  Cu$_2$Fe$_2$Ge$_4$O$_{13}$ is a bicomponent compound that consists of Cu
dimers and Fe chains with separate energy scale. By inelastic neutron
scattering technique with high-energy resolution we observed the indirect Fe -
Fe exchange coupling by way of the Cu dimers. The obtained parameters of the
effective indirect interaction and related superexchange interactions are
consistent with those estimated semi-statically. The consistency reveals that
the Cu dimers play the role of nonmagnetic media in the indirect magnetic
interaction.
