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 in dicate that Mn, clusters in this size range are superparamagnetic species w hose intrinsic moments can be determined within the framework of the Langev in model of paramagnetism. Local minima in per-atom magnetic moments are ob served for Mn-13 and Mn-19, suggestive of an icosahedral growth sequence fo r the smaller size range. For larger clusters, broad oscillations in the pe r-atom moments are observed, with a minimum near Mn32-37 and a maximum arou nd Mn50-56.