  Our recent studies on Co-clusters embedded in various matrices reveal that
the co-deposition technique (simultaneous deposition of two beams : one for the
pre-formed clusters and one for the matrix atoms) is a powerful tool to prepare
magnetic nanostructures with any couple of materials even though they are
miscible. We study, both sharply related, structure and magnetism of the Co/Nb
system. Because such a heterogeneous system needs to be described at different
scales, we used microscopic and macroscopic techniques but also local selective
absorption ones. We conclude that our clusters are 3 nm diameter f.c.c
truncated octahedrons with a pure cobalt core and a solid solution between Co
and Nb located at the interface which could be responsible for the magnetically
inactive monolayers we found. The use of a very diluted Co/Nb film, further
lithographed, would allow us to achieve a pattern of microsquid devices in view
to study the magnetic dynamics of a single-Co cluster.
