Abstract
The electronic structure of has been studied by photoemission and O 1s x-ray-absorption spectroscopy. Spectra of the Mn 2p core levels and the valence bands for and have been analyzed using a configuration-interaction cluster model. The ground state of is found to be mixed and L states and that of to be heavily mixed and L states, reflecting their strong covalency. The character of the band gap of is of the p-to-d charge-transfer type while that of has considerable p-p character as well as p-d character. Holes doped into mainly of oxygen p character are coupled antiferromagnetically with the local moments of the 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 , the so-called in-gap spectral weight (of symmetry) 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 states above the Fermi level decreases, showing a transfer of spectral weight from the unoccupied to the occupied states 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 band and possible orbital fluctuations in the ferromagnetic phase are pointed out.
- Received 25 January 1995
DOI:https://doi.org/10.1103/PhysRevB.51.13942
©1995 American Physical Society