Electronic structure of the two-dimensional negative charge-transfer material Sr3FeMO7 (M=Fe, Co)

M. ABBATE; L. MOGNI; F. PRADO; A. CANEIRO

PHYSICAL REVIEW B

AMER PHYSICAL SOC

Lugar: New York; Año: 2005 vol. 71 p. 95113 - 95118

1098-0121

We studied the relation between the electronic structure and the physical properties of Sr3FeMO7sM=Fe, Cod. The main technique used in the study was Fe 2p, Co 2p, and O 1s x-ray-absorption spectroscopy.The experimental spectra were analyzed in terms of cluster model and band-structure calculations. The analysisof the spectra shows that both Sr3FeFeO7 and Sr3FeCoO7 are in the negative-charge-transfer regime sthismeans that their ground states are highly covalent and contain considerable O 2p hole characterd. The Fe ionsare in a high-spin state and the Co ions in an intermediate-spin state stabilized by strong hybridization. Theelectronic structure helps to explain the trends in the electrical conductivity and the observed magnetic moments.Further, the relatively large O 2p hole weight in the ground state explains also the absence of Jahn-Teller distortions. Sr3FeCoO7 illustrates ferromagnetism and magnetoresistance in a two-dimensional negativecharge-transfer material.