Magnetic properties of free cobalt and gadolinium clusters

Abstract

We report the results of Stern-Gerlach-type magnetic deflection experiments on clusters of cobalt and gadolinium. Cobalt clusters exhibit superparamagnetic behavior over a broad range of temperatures, applied magnetic fields, and cluster sizes. We find an internal magnetic moment per atom of 2.24\ifmmode\pm\else\textpm\fi{}0.14${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$/atom for cobalt clusters containing 65--215 atoms at vibrational temperatures between 85 and 300 K, a value substantially in excess of the bulk value for cobalt. Over a similar temperature range, some gadolinium clusters exhibit superparamagnetic behavior while others exhibit behavior consistent with their moments being locked to their cluster lattices. In both cases, the internal magnetic moments per atom of gadolinium clusters are considerably reduced from the bulk value for gadolinium. The magnetic behaviors of many gadolinium clusters change qualitatively as their vibrational temperatures increase. We also address the current controversy concerning experimental cluster vibrational temperatures.