Structure and magnetism of well defined cobalt nanoparticles embedded in aniobium matrix

Our recent studies on Co clusters embedded in various matrices reveal that the co-deposition technique (simultaneous deposition of two beams: one for the preformed clusters and one for the matrix atoms) is a powerful tool to prepare magnetic nanostructures with any couple of materials even though th ey are miscible. We study both structure and magnetism of the Co/Nb system, which are intimately related. Because such a heterogeneous system needs to be described at different scales, we used microscopic and macroscopic tech niques, and in addition local element selective probes based on x-ray absor ption. We conclude that our clusters are 3-nm-diameter fcc truncated octahe drons with ia pure cobalt core and a solid solution between Co and Nb locat ed at the interface which could be responsible for the magnetically inactiv e monolayers we found.