X-ray absorption of the negative charge-transfer material SrFe_1-xCo_xO₃

We studied the relation between the electronic structure and the phsyiscal properties of SrFe_1-xCo_xO₃. 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 the configuration-interaction cluster model calculation. The analysis of the spectra shows that both SrFeO₃ and SrCoO₃ are in the negative-charge transfer regime (this means that their ground states are mostly covalent and contain considerable O 2p hole character). SrFeO₃ is in a high-spin state and SrCoO₃ in an intermediate-spin state stabilized by strong hybridization. The local electronic structure and the corresponding spin state are mostly preserved in SrFe_1-xCo_xO₃. The relatively large O 2p hole weight in the ground state explains the absence of Jahn-Teller distortions, as well as the relatively large value of the magnetic moment observed at the O sites in these materials. SrFe_1-x Co_xO₃ illustrates both ferromagnetism and magneto-resistance in a negative charge-transfer material.