Titre du document / Document title

Structure and magnetism of Co:CoO core-shell nanoclusters

Auteur(s) / Author(s)

Li X. Z. ⁽¹⁾ ; Wei X. H. ^{(1 2)} ; Skomski R. ^{(1 2)} ; Sellmyer D. J. ^{(1 2)} ;

Affiliation(s) du ou des auteurs / Author(s) Affiliation(s)

⁽¹⁾ Nebraska Center for Materials and Nanoscience, University of Nebraska-Lincoln, NE, Lincoln, USA
⁽²⁾ Department of Physics and Astronomy, University of Nebraska, NE, Lincoln, USA

Résumé / Abstract

Transmission electron microscopy (TEM) and electron diffraction (ED) are used to investigate the nanostructures of two ensembles of Co:CoO core-shell particles. TEM images show that particles of size about 12 nm are almost fully oxidized, while particles with size about 18 nm have a core-shell structure where a Co core is surrounded by a shell of CoO. ED simulation confirms that the larger particles have an fcc-structured Co core and a rock-salt CoO shell structure, while the smaller particles mostly have the rock-salt CoO structure. The core-shell structure is responsible for the unusual magnetic properties of the Co:CoO nanoclusters, especially the occurrence of inverted hysteresis loops (proteresis), but previous research has been indirect, largely based on magnetic measurements and on a cross-comparison with granular materials. Our measurements show that the structures have ferromagnetic fcc Co cores of varying sizes down to 1 nm which are surrounded by antiferromagnetic rock-salt CoO shells. The core radii obtained from the TEM pictures are used to estimate the exchange interactions responsible for proteresis and to pinpoint the core-size window in which proteresis occurs.

Revue / Journal Title

Journal of nanoparticle research    ISSN  1572-896X 

Source / Source

2010, vol. 12, n^o3, pp. 789-794 [6 page(s) (article)]

Langue / Language

Anglais

Editeur / Publisher

Springer, Heidelberg, ALLEMAGNE  (2002) (Revue)

Mots-clés d'auteur / Author Keywords

Nanoparticles

;

Core-shell nanoclusters

;

Magnetic nanostructures

;

Electron microscopy

;

Electron diffraction

;

Localisation / Location

35400060421568.0032