Proceedings of the 9th International Conference on X-Ray Absorption Fine Structure

J. Phys. IV France 7 (1997) C2-409-C2-413
DOI: 10.1051/jp4/1997031

Soft XMCD in Molecule Based Magnets

M.A. Arrio¹, Ph. Sainctavit^{1, 2}, Ch. Cartier dit Moulin², Ch. Brouder^{2, 3}, T. Mallah⁴ and M. Verdaguer<sup>4

1</sup>  Laboratoire de Minéralogie-Cristallographie, URA 9 du CNRS, Universités Paris 6 et 7, 4 place Jussieu, 75252 Paris cedex 05, France
²  Laboratoire pour l'Utilisation du Rayonnement Électromagnétique, CNRS-CEA-MENJS UMR 130, Bât. 209d, 91405 Orsay cedex, France
³  Laboratoire de Physique du Solide de Nancy, URA 155 du CNRS, BP. 239, 54506 Vandœuvre-lès-Nancy, France
⁴  Laboratoire de Chimie des Métaux de Transition, URA 419 du CNRS, Université Paris 6, 4 place Jussieu, 75252 Paris cedex 05, France

Abstract
X-ray absorption spectroscopy at the L_2,3 edges of 3d transition metals has been used to study the electronic structure of molecule based magnets with Curie temperatures ranging from 66 K to 315 K. These magnets 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 taken into account through configuration interaction, we have been able to reproduce nicely the spectra and to determine the exact ground state of the transition metals. We have separated covalence and charge transfer 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_2,3 edges in the ferromagnet Cs^I[Ni^IICr^III(CN)₆]-2H₂0 (T_C = 90 K). With Ligand Field Multiplet calculations the shape of the experimental XMCD signal can be reproduced. The application of the orbital and spin sum rules gives a too small magnetic moment on nickel. A complete calculation taking covalence into account showed that hybridization cannot be responsible for the experimental low nickel magnetic moment.

© EDP Sciences 1997