SUPERPARAMAGNETIC-LIKE BEHAVIOR IN AN OCTANUCLEAR IRON CLUSTER

Using high-frequency EPR spectroscopy we have found that a cluster com prising eight iron(III) ions, Fe-8, which is essentially flat, has a g round S = 10 state and an Ising-type anisotropy. For the first time bo th ac susceptibility and Mossbauer spectroscopy could be used in order to monitor the relaxation time of the magnetization, which was found to follow a thermally activated behavior, as in a superparamagnet, wit h tau(0) = 1.9 x 10(-7) s and an energy barrier of 22.2 K. The set of data allowed us to conclude that the origin of the anisotropy in nanos ize molecular clusters is associated with the single ion contributions and not with the shape of the clusters.