Valence-band spectra and electronic structure ofCuFeO2

Abstract

The delafossite-type ${\mathrm{CuFeO}}_{2}$ 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 ${L}_{\ensuremath{\alpha}},$ Fe ${L}_{\ensuremath{\alpha}},$ and O ${K}_{\ensuremath{\alpha}})$ 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 $\mathrm{LSDA}+U$ 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 ${\mathrm{CuFeO}}_{2}.$ The $\mathrm{LSDA}+U$ calculations give a much better agreement with the observed valence-band structure, the measured electrical, and the magnetic properties.