Structure and magnetism of Co:CoO core-shell nanoclusters

X. Z. Li, X. H. Wei, R. Skomski, D. J. Sellmyer

Research output: Contribution to journalArticle

8 Scopus citations

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.

Original languageEnglish (US)
Pages (from-to)789-794
Number of pages6
JournalJournal of Nanoparticle Research
Volume12
Issue number3
DOIs
StatePublished - Mar 2010

Keywords

  • Core-shell nanoclusters
  • Electron diffraction
  • Electron microscopy
  • Magnetic nanostructures
  • Nanoparticles

ASJC Scopus subject areas

  • Bioengineering
  • Chemistry(all)
  • Atomic and Molecular Physics, and Optics
  • Modeling and Simulation
  • Materials Science(all)
  • Condensed Matter Physics

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