| Abstract
| - Subnanometric cobalt metallic particles, with an average size of 0.8 nm and an estimated numberof 50 atoms, have been stabilized in the confined spaces within the nanopores of crystalline molecularsieves. Remarkably, these clusters show a rapid vanishing of the magnetization as the temperature isincreased from 10 to 20 K because of the ferromagnetic−paramagnetic transition together with thermalfluctuations of the remaining moment. This dramatic reduction of the transition temperature is due to strongfinite size effects. Such behavior, predicted for very small metallic particles, was never observed beforedue to the inherent difficulty in achieving subnanometric stable metallic particles.
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