SOFT XMCD IN MOLECULE BASED MAGNETS

X-ray absorption spectroscopy at the L-2,L-3 edges of 3d transition me tals has been used to study the electronic structure of molecule based magnets with Curie temperatures ranging from 66 K to 315 K. These mag nets are bimetallic cyanides of the Prussian blue family, constructed by a three dimensional assembling of -NC-Cr-III-CN-A(II)- units. Using Ligand Field Multiplet calculations, where hybridization is mainly ta ken into account through configuration interaction, we have been able to reproduce nicely the spectra and to determine the exact ground stat e of the transition metals. We have separated covalence and charge tra nsfer effects occurring in the bond between the 3d ions and the cyano ligand. We have also recorded X-ray Magnetic Circular Dichroism (XMCD) at nickel L-2,L-3 edges in the ferromagnet Cs-I[(NiCrIII)-Cr-II(CN)(6 )]. 2H(2)O (T-C = 90 K). With Ligand Field Multiplet calculations the shape of the experimental XMCD signal can be reproduced. The applicati on of the orbital and spin sum rules gives a too small magnetic moment on nickel. A complete calculation taking covalence into account showe d that hybridization cannot be responsible for the experimental low ni ckel magnetic moment.