Multiple-Structure Optical Spectral Weight Transfer in Ferromagnetic EuB6

We have obtained the optical conductivity of EuB6 over a wide range from 2 meV to 5.5 eV from reflectivity and ellipsometry measurements. At the ferromagnetic transition (T-c = 15.5 K) (1) sigma(1)(omega) was found to decrease at three different energies w = 0.5, 1.4 and 2.75 eV and (2) the lost spectral weight was found to be recovered in the Drude conductivity. We show that these unusual multiple-structure optical conductivity changes can be explained by using the spin-dependent splitting of the electronic bands at the ferromagnetic phase.