MEASUREMENT OF MAGNETIC-MOMENT AT THE ATOMIC-SCALE IN A HIGH T-C MOLECULAR-BASED MAGNET

The molecular-based magnet Cs-I[(NiCrIII)-Cr-II(CN)6]. 2H(2)O is a fer romagnetic with a Curie temperature T-C = 90 K. Its structure consists of face-centered cubic lattice of Ni-II ions connected by Cr(CN)(6) e ntities. We have recorded X-ray magnetic circular dichroism (XMCD) at nickel L(2,3) edges. It clearly evidences that nickel(II) is in a high -spin configuration and ferromagnetically coupled to the surrounding C r-III. Through ligand field multiplet calculations, we have determined the total magnetic moment carried by Ni-II. Special attention has bee n paid to the magnetic anisotropy that complicates the calculation of the cross section for a powder. By using sum rules derived for XMCD, i t has been possible to extract the orbital and spin contributions to t he total magnetic moment. A somewhat too small magnetic moment is foun d on nickel. A complete calculation taking into account the multiplet coupling effect and the covalent hybridization allowed to determine th e precise ground state of nickel and showed that hybridization cannot be responsible for the experimental low nickel magnetic moment. The or igin of this effect is discussed.