J. Phys. I France
Volume 4, Numéro 2, February 1994
Page(s) 273 - 282
DOI: 10.1051/jp1:1994137
J. Phys. I France 4 (1994) 273-282

Low temperature dynamics of small $\gamma$-Fe 20 3 particles

E. Vincent1, J. Hammann1, P. Prené2 and E. Tronc2

1  Service de Physique de l'Etat Condensé, C.E.A. Saclay, Orme des Merisiers, 91191 Gif-surYvette Cedex, France
2  Laboratoire de Chimie de la Matière Condensée, C.N.R.S. (URA 1466), Université Pierre et Marie Curie, 4 place Jussieu, 75252 Paris Cedex 05, France

(Received 15 October 1993, accepted 1 December 1993)

We have studied the response of a system of small (~ 4 nm) ferrimagnetic particles to a field reversal at low temperature (0.6 to 12 K). The reversal of the particle magnetic moments through the anisotropy barriers is shown to be governed by thermally activated dynamics down to 0.6 K, with no evidence for quantum effects. We propose a data analysis in terms of the unique variable $T \cdot Ln(\frac{t}{\tau_0})$, which accounts for a non-constant distribution of anisotropy barriers.

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