MAGNETIC-PROPERTIES OF FREE COBALT AND GADOLINIUM CLUSTERS

We report the results of Stern-Gerlach-type magnetic deflection experi ments on clusters of cobalt and gadolinium. Cobalt clusters exhibit su perparamagnetic behavior over a broad range of temperatures, applied m agnetic fields, and cluster sizes. We find an internal magnetic moment per atom of 2.24+/-0.14mu(B)/atom for cobalt clusters containing 65-2 15 atoms at vibrational temperatures between 85 and 300 K, a value sub stantially in excess of the bulk value for cobalt. Over a similar temp erature range, some gadolinium clusters exhibit superparamagnetic beha vior while others exhibit behavior consistent with their moments being locked to their cluster lattices. In both cases, the internal magneti c moments per atom of gadolinium clusters are considerably reduced fro m the bulk value for gadolinium. The magnetic behaviors of many gadoli nium clusters change qualitatively as their vibrational temperatures i ncrease. We also address the current controversy concerning experiment al cluster vibrational temperatures.