Nano Archive

Structure and magnetism of Co:CoO core-shell nanoclusters

Li, X. and Skomski, R. and Sellmyer, D. (2010) Structure and magnetism of Co:CoO core-shell nanoclusters. Journal of Nanoparticle Research, 12 (3). pp. 789-794.

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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.

Item Type:Article
ID Code:9124
Deposited By:Prof. Alexey Ivanov
Deposited On:13 May 2010 12:53
Last Modified:13 May 2010 13:19

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