THERMAL-PROPERTIES OF FERROMAGNETIC CLUSTERS

The magnetic moments and heat capacities of small iron, cobalt and nic kel clusters in a molecular beam have been measured as a function of t heir size and temperature. The magnetic moment of nickel and cobalt cl usters decreases with increasing size and with increasing temperature, slowly converging to the bulk magnetization curve as the cluster size increases. Heat capacity measurement of the clusters in the beam reve als that the magnetic contribution to the heat capacity is well approx imated using mean field concepts, combined with measured magnetic prop erties. In contrast, iron clusters show anomalies, both in the magneti c moments as well as in the heat capacities. We speculate that these e ffects reflect a sensitivity of the magnetic order on structure as in bulk iron.