Magnetic Properties of Nanoparticles of Antiferromagnetic Materials

Springer Science and Business Media LLC - 2002
Steen MØrup1, Cathrine Frandsen1, Franz BØdker1, Stine Nyborg Klausen2, Kim Lefmann2, Per-Anker LindgÅrd2, Mikkel Fougt Hansen3
1Department of Physics, Technical University of Denmark, Kgs Lyngby, Denmark
2Materials Research Department, Risø, National Laboratory, Roskilde, Denmark
3Mikroelektronik Centret, Technical University of Denmark, Kgs. Lyngby, Denmark

Tóm tắt

The magnetic properties of antiferromagnetic nanoparticles have been studied by Mössbauer spectroscopy and neutron scattering. Temperature series of Mössbauer spectra of non-interacting, superparamagnetic hematite nanoparticles were fitted by use of the Blume-Tjon relaxation model. It has been found that the magnetic anisotropy energy constant increases significantly with decreasing particle size. Neutron scattering experiments on similar samples give new information on both superparamagnetic relaxation and collective magnetic excitations. There is good agreement between the values of the parameters obtained from Mössbauer spectroscopy and neutron scattering. In samples of interacting hematite nanoparticles, the relaxation was significantly suppressed. The Mössbauer data for these samples are in accordance with a mean field model for an ordered state of strongly interacting particles. Mixing nanoparticles of hematite with CoO nanoparticles resulted in suppression of the superparamagnetic relaxation, whereas NiO nanoparticles had the opposite effect.

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