In this work we report on the magnetic characterization of thin films composed of gas-phase cobalt nanoclusters deposited on surfaces. Measurements of magnetization curves at ambient temperature indicate a strong exchange interaction between the clusters, while at cryogenic temperatures an exchange bias field appears. The latter confirms the existence of a ferromagnetic/antiferromagnetic core-shell system. Temperature-dependent magnetization measurements under zero-field-cooled conditions showed a rather broad maximum situated around 200 K. Magnetic force microscopy indicates the formation of a correlated super-spin-glass (CSSG) resulting from the frustration between the interparticle exchange interaction and the randomly oriented intraparticle anisotropy. The approach to saturation of the magnetization curves at 295 K is consistent with a CSSG.

• Received 3 September 2004

DOI:https://doi.org/10.1103/PhysRevB.71.085410