The European Physical Journal B

, Volume 14, Issue 4, pp 681–689

Surface effects in nanoparticles: application to maghemite -Fe O

  • H. Kachkachi
  • A. Ezzir
  • M. Noguès
  • E. Tronc
Article

DOI: 10.1007/s100510051079

Cite this article as:
Kachkachi, H., Ezzir, A., Noguès, M. et al. Eur. Phys. J. B (2000) 14: 681. doi:10.1007/s100510051079

Abstract:

We present a microscopic model for nanoparticles, of the maghemite-Fe2O3) type, and perform classical Monte Carlo simulations of their magnetic properties. On account of Mössbauer spectroscopy and high-field magnetisation results, we consider a particle as composed of a core and a surface shell of constant thickness. The magnetic state in the particle is described by the anisotropic classical Dirac-Heisenberg model including exchange and dipolar interactions and bulk and surface anisotropy. We consider the case of ellipsoidal (or spherical) particles with free boundaries at the surface. Using a surface shell of constant thickness nm) we vary the particle size and study the effect of surface magnetic disorder on the thermal and spatial behaviors of the net magnetisation of the particle. We study the shift in the surface “critical region” for different surface-to-core ratios of the exchange coupling constants. It is also shown that the profile of the local magnetisation exhibits strong temperature dependence, and that surface anisotropy is responsible for the non saturation of the magnetisation at low temperatures.

PACS. 75.50.Tt Fine particle systems - 75.30.Pd Surface magnetism - 75.10.Hk Classical spin models

Copyright information

© EDP Sciences, Springer-Verlag, Società Italiana di Fisica 2000

Authors and Affiliations

  • H. Kachkachi
    • 1
  • A. Ezzir
    • 1
  • M. Noguès
    • 1
  • E. Tronc
    • 2
  1. 1.LMOV (CNRS UMR 8634), Université de Versailles St. Quentin, 45 avenue des États-Unis, 78035 Versailles Cedex, FranceFrance
  2. 2.LCMC (CNRS URA 1466), Université Pierre & Marie Curie, 4 place Jussieu, 75252 Paris Cedex, FranceFrance