Experimental Observation of Superparamagnetism in Manganese Clusters

A molecular beam of manganese clusters, Mn _n (n  =  11–99), produced at 68 K is deflected toward high field by a gradient field magnet. These results indicate that Mn _n clusters in this size range are superparamagnetic species whose intrinsic moments can be determined within the framework of the Langevin model of paramagnetism. Local minima in per-atom magnetic moments are observed for Mn ₁₃ and Mn ₁₉, suggestive of an icosahedral growth sequence for the smaller size range. For larger clusters, broad oscillations in the per-atom moments are observed, with a minimum near Mn _32–37 and a maximum around Mn _50–56.