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).