The electronic structures of a wide range of transition-metal compounds, including Cu, Ni, Co, Fe, and Mn oxides and sulfides, with metal valences ranging from 2+ to 4+, have been investigated by a cluster-type configuration-interaction analysis of the core-level 2p x-ray photoemission spectra. We show that by including the d-d exchange interaction (retaining only diagonal terms) and an anisotropic metal-ligand hybridization in the model, these spectra can be well reproduced, and so can be used to deduce quantitatively values for the ligand-to-metal charge-transfer energy 5, the on-site d-d Coulomb repulsion energy U, and the metal-ligand transfer integrals T. Systematics for 6 and U are generally consistent with those found from previous valence-band studies and follow expected chemical trends. By using values of 5 and U found from this model, we show that most of the transition-metal compounds studied in this work can be classified in the charge-transfer regime of the Zaanen-Sawatzky-Allen diagram. A few exceptions to these systematics have been found. Small U values found for pyrite-type CoS& and FeS2 and large T values for Mn perovskite oxides, as well as the neglect of other mechanisms such as exciton satellites, may indicate a limitation of the local-cluster model.

The electronic structure of Lal Sr MnQ3 has been studied by photoemission and Q 1s x-rayabsorption spectroscopy. Spectra of the Mn 2p core levels and the valence bands for LaMnQ3 and SrMnQ3 have been analyzed using a configuration-interaction cluster model. The ground state of LaMnQ3 is found to be mixed d and d I states and that of SrMnQ3 to be heavily mixed d and d 1.states, rejecting their strong covalency. The character of the band gap of LaMnQ3 is of the p-to-d charge-transfer type while that of SrMnQ3 has considerable p-p character as well as p-d character. Holes doped into LaMnQ3 mainly of oxygen p character are coupled antiferromagnetically with the d local moments of the Mn + ions and become itinerant, thus aligning the Mn moments ferromagnetically. The changes in the electronic structure with carrier doping are not of the rigid band type: By La substitution for SrMnQ3, the so-called in-gap spectral weight (of e"~s ymmetry) appears with its peak located 1 -2 eV below the Fermi level and grows in intensity with increasing La concentration, while the spectral intensity of the eg~s tates above the Fermi level decreases, showing a transfer of spectral weight from the unoccupied to the occupied eg~s tates with electron doping. Meanwhile, the intensity at the Fermi level remains low even in the metallic phase (0.2~x~0.6). The energy shifts of core-level peaks and valence-band features with x suggest a downward shift of the Fermi level with hole doping, but the shift is found to be very small in the metallic phase. The importance of the orbital degeneracy of the e~~b and and possible orbital fiuctuations in the ferromagnetic phase are pointed out.

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The k-dependent electronic structure of the low temperature ferromagnetic state of La 1.2 Sr 1.8 Mn 2 O 7 was measured using angle-resolved photoemission spectroscopy and calculated using the local spin density approximation (LSDA). The measured near-Fermi energy states display E vs k and symmetry relationships which agree relatively well with the LSDA prediction through much of the Brillouin zone, and the locus of lowest energy excitations matches the predicted large Fermi surface quite well. However, the spectral features are too broad to be well described as Fermi-liquid-like quasiparticles, and they are strongly suppressed from the Fermi energy, i.e., there is a pseudogap in the excitation spectrum. We discuss the spectral properties in terms of strong coupling to a local effect such as a lattice distortion. [S0031-9007(98)06522-3]