Multiple Scattering Analysis of O KEdge NEXAFS in Iron Oxides

We report a detailed analysis of O K-edges near edge x-ray absorption of maghemite, hematite and magnetite iron oxides. Measurements were performed on powder in Fluorescence Yield mode of detection. Iron forms several stable oxides and its phase diagram is more complicated than that of other transition metal as Ni or Co. The differences in the local symmetry of the three iron oxides are related with the distinguishable NEXAFS spectra. In particular the spectra are characterized by a sharp doublet ascribable to transitions to the empty metal d-bands involving the t2g and eg states whose energy splitting and intensities depend on the structure and state of ionicity. The NEXAFS spectra have been simulated and fitted by MXAN code. The aim of these simulations was the test of light Z element NEXAFS spectra calculation performed by phenomenological no-self-consistent potential in the near edge region, the most sensible to electronic properties details; a fit procedure of the potential parameters was performed in the extended NEXAFS photon energy range and subsequently used for near edge calculations. The MXAN simulations obtained in this way, reproduce the experimental data with good agreement and evidentiate the differences in the spectra of the three compounds. In particular maghemite, that has oxygen in two different sites, has been well simulated using potential details found for the other oxides hematite and magnetite.