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Título

Observation of Co/CoO nanoparticles below the critical size for exchange bias

AutorDobrynin, A. N.; Temst, K.; Lievens, P.; Margueritat, J. ; Gonzalo de los Reyes, José; Afonso, Carmen N. ; Piscopiello, E.; Van Tendeloo, G.
Palabras claveCobalt
Cobalt compounds
Ferromagnetic materials
Antiferromagnetic materials
Fecha de publicación11-jun-2007
EditorAmerican Institute of Physics
CitaciónJournal of Applied Physics 101(11): 113913 (2007)
ResumenWe compare the magnetic properties of pure and oxidized Co nanoparticles embedded in an amorphous Al2O3 matrix. Nanoparticles with diameters of 2 or 3 nm were prepared by alternate pulsed laser deposition in high vacuum conditions, and some of them were exposed to O2 after production and before being embedded. The nanoparticles are organized in layers, the effective edge-to-edge in-depth separation being 5 or 10 nm. The lower saturation magnetizations per Co atom for the samples containing oxidized nanoparticles provide evidence for the formation of antiferromagnetic CoO shells in the nanoparticles. None of the samples with Co/CoO nanoparticles show exchange bias, while vertical hysteresis loop shifts and enhanced coercivities (as compared to samples with pure Co nanoparticles) are observed. This constitutes evidence for the nanoparticles size being in all cases smaller than the critical size for exchange bias. The difference in coercivity versus temperature dependences for the samples with pure and oxidized Co nanoparticles shows that the exchange anisotropy in Co/CoO nanoparticles appears at temperatures lower than 50 K.
Descripción7 pages, 11 figures, 2 tables.-- PACS: 75.50.Cc; 75.50.Ee; 75.50.Tt; 75.30.Et; 75.60.Ej; 61.46.Df
Versión del editorhttp://dx.doi.org/10.1063/1.2736303
URIhttp://hdl.handle.net/10261/21754
DOI10.1063/1.2736303
ISSN0021-8979
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