Experimental band structure of the nearly half-metallic CuCr2Se4: an optical and magneto-optical study

Diagonal and off-diagonal optical conductivity spectra have been determined from the measured reflectivity and magneto-optical Kerr effect over a broad range of photon energies in the itinerant ferromagnetic phase of CuCr2Se4 at various temperatures down to T = 10 K. Besides the low-energy metallic contribution and the lower-lying charge transfer transition at E approximate to 2 eV, a sharp and distinct optical transition was observed in the mid-infrared region around E = 0.5 eV with huge magneto-optical activity. This excitation is attributed to a parity allowed transition through the Se-Cr hybridization-induced gap in the majority spin channel. The large off-diagonal conductivity is explained by the high-spin polarization in the vicinity of the Fermi level and the strong spin-orbit interaction for the related charge carriers. The results are discussed in connection with band structure calculations.