Magnetism in Nanoclusters and Cluster-Assembled Thin Films
Abstract:Increasing attention has been focused on the magnetic behavior of nanoparticles with diameters of 1–5 nm (~50–5000 atoms). In this size range fundamental magnetic parameters such as the orbital and spin magnetic moments per atom deviate significantly from bulk values, and studying clusters addresses fundamental problems in mesoscopic magnetism, which is not as well understood as in either the atomic or the bulk regimes. There is also a growing realization of the enormous industrial potential of materials built by depositing preformed nanoclusters instead of atoms. If the clusters are size-selected and deposited in conjunction with an atomic vapor of a matrix material, it is possible to produce granular films in which there is independent control over the particle size and volume fraction. Using this technique, it also becomes possible to make granular mixtures of miscible materials. This unprecedented degree of control over the properties of the films holds the promise of new magnetic materials with "engineered properties." To fully realize this potential requires a greater understanding of not only the individual particles, but also how they interact in dense assemblies. There has been great progress in understanding some aspects of the magnetic behavior of nanoclusters and cluster-assembled materials. The mechanisms that generate spin and orbital moments that are enhanced by up to 36 and 200%, respectively, relative to the bulk in isolated clusters are well understood as is the dynamical behavior of the magnetic moment. Not so well understood is the observed magnetic anisotropy, which often has a different symmetry than the bulk. In dense assemblies, the nature of the interparticle coupling and the relative importance of dipolar and exchange interactions also require further research.
Document Type: Review Article
Affiliations: Department of Physics and Astronomy, University of Leicester, Leicester LE1 7RH, UK
Publication date: 2001-09-01
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