Magnetization reversal of a 1000-atoms cobalt cluster

In this paper, we report recent experimental results on the magnetic proper ties of 1000-atoms cobalt clusters embedded in a niobium superconducting ma trix. From macroscopic measurements on cluster assemblies we deduce their a verage structural and magnetic properties. Furthermore, using an improved m icro-SQUID device coupled with an original cluster deposition technique, we detect the magnetization reversal of a single cobalt cluster and measure t he spatial distribution of the switching field at low temperature (T = 35 m K). A detailed study of the corresponding surface leads to a first interpre tation of the origin of the anisotropy in such nanosize particles. (C) 2001 Published by Elsevier Science B.V.