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Magnetic dynamics of Co Nanospheres: origin of the enhanced anisotropy.

AuthorsBartolomé, Juan; Bartolomé, Fernando; García, L. M.; Luis, Fernando
Issue Date26-May-2006
CitationSmart Materials for Ranging Systems 226: 1-25 (2006)
AbstractThe present work deals with the observation of enhancement of the magnetic anisotropy of Co nanoparticles and its origin. The samples were granular multilayer samples prepared by sequential deposition, by sputtering, of amorphous Al2O3 and Co layers on a Si substrate. Co nanoparticles are selforganized in a quasi-regular spatial order of approximately hexagonal closepacked symmetry. The particles studied range in average diameter 〈D〉 between 0.7 nm and nearly 5 nm, with a narrow size distribution. This well controlled morphology has enabled us to circumvent ambiguities in sample configuration and, by means of a simple model for fluctuating moments, explain the dynamics of the Co particle moments in terms of an activation energy with contributions from anisotropy Keff, dipole-dipole interactions Edip, and a bias magnetic field H. The anisotropy is enhanced by one to two orders of magnitude with respect to the bulk fcc Co due to strong pinning of the surface Co magnetic moments anisotropy, and increase as 1/D as the particle diameter decreases. The origin of this enhancement is related to an increase of the orbital magnetic moment at the surface atoms. Capping the Co nanospheres with a Cu film increases further the particle anisotropy and the orbital magnetic moment of the surface atoms.
Description25 pages, 16 figures, 1 table.-- et al.
Publisher version (URL)http://dx.doi.org/10.1007/1-4020-4646-4
Appears in Collections:(ICMA) Artículos
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