IMPROVED DETERMINATION OF BACKSCATTERING AMPLITUDE AND PHASE SHIFT FUNCTIONS

Procedures for analysis of EXAFS data require knowledge of the phase shift and amplitude functions, Φ(k) and B(k). We present procedures to obtain these functions, both experimentally and theoretically, that overcome limitations in presently available methods. A procedure is described that allows for the use of crystallographically complex materials to serve as standards in the experimental determination of Φ(k) and B(k). Also we present a convenient algorithm, that uses the full curved wave formalism, to determine the functions theoretically. Improved results are obtained, particularly at low k. We illustrate the use of these procedures with a study of the 3d transition metals

EXAFS study of local order and structure in Cu-doped manganites

We report extended X-ray absorption fine structure measurements at the Mn K edge on (La0.63Ca037) (Mn0.92Cu0.08)O3 and (La0.25Ca075)(Mn0.92Cu0.08)O3 samples. We observe that the Cu2+ substitution in these two compounds belonging from the opposite sides of the phase diagram induces two very different effects. In the first case, it weakens ferromagnetic ordering, while in the second one, it does not significantly modify the charge ordering present in the system