Comparison between extended x-ray-absorption and extended electron energy-loss fine-structure results above theM2,3edge of cobalt

An electron energy-loss fine-structure (EELFS) experiment has been carried out above the $M_2$,3 edge of a cobalt single crystal. These results are compared with extended x-ray-absorption fine-structure (EXAFS) data taken on the same sample (and using the same experimental apparatus) by using the partial-yield technique. The use of the usual EXAFS analysis on the two sets of data gives practically identical results (within experimental accuracy). However, the nearest-neighbor distance that can be calculated by using theoretical phase shifts [W. Ekardt and D. B. Tran Thoai, Solid State Commun. 45, 1083 (1983)] is less in both cases by about 0.2 Å with respect to the known value. We conclude that the matrix element involved in the energy-loss excitation of the Co $M_2$,3 core level in the EELFS experiment has a prevalent dipole contribution. This important result implies that the usual EXAFS analytical technique for determining lattice parameters can also be applied to EELFS data. We conclude also that the theoretical phase shift calculated within the Z+1 approximation is not adequate for the analysis of 3p-edge fine structures.