Diffraction anomalous fine structure of forbidden Bragg reflections: charge localization and structure of the octahedral site in magnetite

Resonant X ray scattering has been used to investigate charge localization on the octahedral iron atoms in magnetite below and above the Verwey temper ature. We have measured the DAFS spectra of the 002 and 006 "forbidden" Bra gg reflections permitted by the anisotropy of the iron anomalous scattering factor. We performed ab initio calculations which are in fair agreement wi th the experiment in the near edge region and demonstrate the sensitivity o f the DAFS spectra to tiny structural and electronic changes. No change is observed, in the energy and azimuthal dependences, when the sample is coole d down below the Verwey temperature. Charge ordering can be definitely excl uded and different charge localisation schemes discarded. Ab initio simulat ions, performed by using the refined crystallographic structure proposed fo r the room temperature phase, do not show a good agreement with the experim ent in the extended region of the DAFS spectrum. This point is being invest igated.