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 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.Comment: 7 TeX pages, 9 Postscript figures, detailed heading adde

EXAFS study of local order and structure in Cu-doped manganites

We report extended X-ray absorption fine structure measurements at the Mn K edge on (La0.63Ca037) (Mn0.92Cu0.08)O3 and (La0.25Ca075)(Mn0.92Cu0.08)O3 samples. We observe that the Cu2+ substitution in these two compounds belonging from the opposite sides of the phase diagram induces two very different effects. In the first case, it weakens ferromagnetic ordering, while in the second one, it does not significantly modify the charge ordering present in the system