Accurate determination of anomalous scattering factor near Fe K absorption edge

When X-ray energy is close to the absorption edge, the anomalous scattering factor changes drastically and the determination of the real part f'(E) becomes important for crystal-structure analyses. The resonant X-ray diffraction technique has been applied to distinguish crystallographically independent sites of magnetite (Fe3O4), which has the inverse-spinel structure with tetrahedral A and octahedral B sites. In this study, we have site-selectively estimated f' values for the different Fe sites by using X-ray diffraction data measured at Fe K edge. The intensity data were collected at two X-ray energies, Eon (=7.1082 keV) and Eoff (=7.1051 keV), corresponding to on- and off-peaks of the Fe pre-edge. Through the least-squares calculation to refine f'(E) as an unknown parameter, the f'(E) values of Fe³⁺ for A and B sites were determined to be -7.680 and -7.855 at Eon and -6.682 and -6.709 at Eoff, respectively. These values are in a good agreement with -7.943 for total Fe ions, obtained from the absorption data of NiFe2O4 in the inverse-spinel structure.