Electronic structure of the two-dimensional negative charge-transfer material Sr3FeMO7 (M=Fe, Co) -: art. no. 195113

We studied the relation between the electronic structure and the physical properties of Sr3FeMO7 (M=Fe, Co). 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 analysis of the spectra shows that both Sr3FeFeO7 and Sr3FeCoO7 are in the negative-charge-transfer regime (this means that their ground states are highly covalent and contain considerable O 2p hole character). The Fe ions are in a high-spin state and the Co ions in an intermediate-spin state stabilized by strong hybridization. The electronic 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 negative-charge-transfer material.