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

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Diagonal and off-diagonal optical conductivity spectra have been determined form the measured reflectivity and magneto-optical Kerr effect (MOKE) over a broad range of photon energy 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≈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.