Journal of Nanoparticle Research

, Volume 12, Issue 3, pp 789–794 | Cite as

Structure and magnetism of Co:CoO core–shell nanoclusters

  • X. Z. Li
  • X. H. Wei
  • R. Skomski
  • D. J. Sellmyer
Research Paper


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.


Nanoparticles Core–shell nanoclusters Magnetic nanostructures Electron microscopy Electron diffraction 



This research is supported by NSF-MRSEC (Grant No. NSF-DMR-0820521) and NCMN.


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Copyright information

© Springer Science+Business Media B.V. 2009

Authors and Affiliations

  • X. Z. Li
    • 1
  • X. H. Wei
    • 1
    • 2
  • R. Skomski
    • 1
    • 2
  • D. J. Sellmyer
    • 1
    • 2
  1. 1.Nebraska Center for Materials and NanoscienceUniversity of Nebraska-LincolnLincolnUSA
  2. 2.Department of Physics and AstronomyUniversity of NebraskaLincolnUSA

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