Valence-band spectra and electronic structure of CuFeO2

The delafossite-type CuFeO2 single crystal was studied by means of x-ray emission and x-ray photoelectron spectroscopy. The valence state of Cu ions was found to be 1 +, whereas Fe ions were found to be trivalent in the high-spin S = 5/2 state. The x-ray emission (Cu L-alpha, Fe L-alpha, and O K-alpha) and photoelectron spectra were compared to the results of the local spin density approximation (LSDA) (full-potential linearized augmented plane wave method and linearized muffin-tin orbitals in atomic sphere approximation method) and LSDA + U calculations. It is found that the maximum of the Cu 3d state distribution is localized closer to the Fermi level than that of the Fe 3d states. The LSDA calculations contradict the experimental results and do not give a correct description of the Cu and Fe 3d positions relative to the Fermi level, and incorrectly predict metallic behaviors (semiconductor observed) and give qualitatively incorrect magnetic properties of CuFeO2. The LSDA + U calculations give a much better agreement with the observed valence-band structure, the measured electrical, and the magnetic properties.