Magnetic Anisotropy in the [Cu^IILTb^III(hfac)₂]₂Single Molecule Magnet: Experimental Study and Theoretical Modeling

In the present article, we proffer an explanation for the origin of single molecule magnetism in [Cu II LTb III (hfac) 2 ] 2, a member of the novel class of mixed transition−lanthanide metal clusters. The theoretical model takes into account the crystal field acting on the Tb III ion as well as the exchange interaction between the Tb III and Cu II ions and provides a good account of the low-lying energy levels, rigorously measured by inelastic neutron scattering and magnetic data. We demonstate that the single molecule magnet (SMM) behavior is not a sole consequence of the low-lying levels of the lanthanide metal ion but a property of the tetranuclear cluster itself. The energy levels are shown to increase with the decrease of the mean value of the Z-projection of the total angular momentum of the cluster, thus forming a barrier for magnetization reversal that is wholly consistent with the observed SMM behavior. On the basis of this study, recommendations are formulated on how the SMM properties for n d−4f clusters may be further improved.