Structure and magnetism of well defined cobalt nanoparticles embedded in a niobium 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 they 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 techniques, and in addition local element selective probes based on x-ray absorption. We conclude that our clusters are 3-nm-diameter fcc 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.