Quantitative evaluation of quadrupole transition effect in ATS scattering from magnetite, Fe3O4

Abstract

ATS (anisotropic tensor of the susceptibility) scattering can be observed in the forbidden Bragg reflections near the absorption edge. This scattering is sensitive to the electronic states in anisotropic environment, especially to the direction of the electronic orbital. We have studied the ATS scattering in iron pyrite (FeS2), magnetite (Fe3O4) and so on.[1] These experimental results above the edge are in good agreement with the calculation based on the electric dipole transition. Below the edge, however, the effects of quadrupole transition have been observed. Magnetite has a spinel structure, in which the Fe atoms occupy the tetrahedral A site and the octahedral B site. The ATS scattering with dipole-dipole (d-d) transition process is allowed for the B site but not allowed for the A site because of the site symmetry. For the A site, therefore, we must consider more higher approximation, dipole-quadrupole (d-q) term. (For the B site the d-q scattering is not allowed.) We previously studied the energy and azimuthal angle dependence of the 002 and 006 forbidden reflections.[2] We observed two resonant peaks in energy spectrum near the Fe K-absorption edge. The main resonant peak is just above the edge and the second peak in the pre-edge region. From the difference of the two reflection intensities we concluded that the main peak was mainly caused by d-d scattering from the B site and the pre-edge peak by d-q scattering from the A site. However, we did not quantitatively evaluate each contribution because the azimuth dependence is completely same in both scattering. In the present report we investigated the 046 forbidden reflection in order to estimate the quantitative contribution from the A and B sites.