Surface properties and magnetic relaxation of metallic iron nanoparticles

  • Bødker, Franz (Project Manager)
  • Mørup, Steen (Project Participant)
  • Rasmussen, Helge Kildahl (Project Participant)
  • Chorkendorff, Ib (Project Participant)
  • Pedersen, Michael S. (Project Participant)
  • Svedlindh, Peter (Project Participant)
  • Jonsson, G.T. (Project Participant)
  • Garcia-Palacios, J.L. (Project Participant)
  • Lazaro, F.J. (Project Participant)

Project Details

Description

We have studied nanoparticles of metallic iron with sizes of 2-4 nm which are very difficult to handle as they will oxidize immediately in the presence of oxygen. Therefore we have developed a new type of in situ cell which allows us to perform Mössbauer spectroscopy under optimal condition with the possibility of controlling the environment of the particles. With this type of cell we were also able to perform magnetization measurements and neutron scattering.
Nanoparticles have a large fraction of their atoms in the surface and the particles will therefore be influenced by the properties of the surface atoms. Such small particles are thus very sensitive to chemisorption of gasses. With Mössbauer spectroscopy we have studied the effect of chemisorption of oxygen, carbon monoxide and nitrogen on the surface. We found that oxygen results in a ferromagnetic oxide overlayer, while carbon monoxide results in diamagnetism and nitrogen gives a broad distribution of magnetic moment in the particle surface.
Due to the small size of the nanoparticles it is possible to observe size effects such as superparamagnetic relaxation which is a thermally activated fluctuation of the magnetic particle moment. The frequency of these fluctuations was found to vary 11 orders of magnitude in the studied temperature range in good agreement with theoretical predictions. These results are among some of the first consistent measurements of this type and the very first on metallic iron particles.
StatusFinished
Effective start/end date01/01/199631/12/1996