Investigating molecular magnetism with polarized neutrons

Abstract

The determination of magnetization density distributions using polarized neutron diffraction has played a key role during the last fifteen years in the emerging field of molecular magnetism. In the present article, an introduction to this branch of material science and to the experimental technique is given. The data treatment methods are briefly reviewed and some recent results are presented. A particular attention is given to the members of the nitronyl nitroxide free radicals family, which are widely used in the construction of organic magnetically ordered materials. The main features of the magnetization density in isolated radicals are presented. Spin polarization and spin delocalization effects encountered in this class of compounds are discussed. Then it is shown how the magnetic interactions with neighbouring molecules can propagate through hydrogen bonds or through intermediate atoms and how they modify the main features found in isolated species. In the case of a direct coordination to a transition metal ion, it is shown how drastic can be the modifications on the spin density, depending on the strength of the magnetic couplings.