Using a new microSQUID set-up, we investigate magnetic anisotropy in a single 1000-atoms cobalt cluster. This system opens new fields in the characterization and the understanding of the origin of magnetic anisotropy in such nanoparticles. For this purpose, we report three-dimensional switching field measurements performed on a 3 nm cobalt cluster embedded in a niobium matrix. We are able to separate the different magnetic anisotropy contributions and evidence the dominating role of the cluster surface.

International audienc

Because of its superior properties silicon carbide is one of the most promising materials for power electronics, hard- and biomaterials. In the solid phase, the electronic and optical properties are controlled by the stacking of double layers of Si and C atoms. In thin films, a change in the stacking order often requires stress, which can be achieved naturally in systems with nanometre length scale. For this reason, nanotubes, nanowires and clusters can be used as building blocks for the synthesis of novel materials. Furthermore, playing at the nanometre length scale enables the nature of the SiC bonding to be modified, which is of prime importance for atomic engineering of nanostructures. In this review, emphasis is placed on the theoretical principles associated with SiC cage-like clusters and experimental work resulting from them.

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In this paper the specific properties of free clusters and the formation of new cluster-assembled materials using the low energy cluster beam deposition (LECBD) technique are discussed. Recent results obtained for free clusters are summarized with special attention to new observed structures. As for the specific structures and properties of cluster-assembled materials, two main aspects are specially emphasized: the memory effect of the free cluster properties leading to the formation of new phases and the effect of the specific nanostructure of the cluster-assembled materials related to the random cluster stacking mechanism characteristic of the LECBD. These effects and the corresponding potential applications are illustrated using some selected examples: new diamond-like carbon films produced by fullerene depositions (memory effect) and grain effect on the magnetic properties of cluster-assembled transition metal films.

We present a joint experimental and theoretical study of the superconductivity in doped silicon clathrates. The critical temperature in Ba(8)@Si-46 is shown to strongly decrease with applied pressure. These results are corroborated by ab initio calculations using MacMillan's formulation of the BCS theory with the electron-phonon coupling constant lambda calculated from perturbative density functional theory. Further, the study of I(8)@Si-46 and of gedanken pure silicon diamond and clathrate phases doped within a rigid-band approach show that the superconductivity is an intrinsic property of the sp(3) silicon network. As a consequence, carbon clathrates are predicted to yield large critical temperatures with an effective electron-phonon interaction much larger than in C60.

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