Europhys. Lett.
Volume 62, Number 5, June 2003
Page(s) 650 - 656
Section General
Published online 01 May 2003
DOI: 10.1209/epl/i2003-00423-y
Europhys. Lett., 62 (5) , pp. 650-656 (2003)

Effect of exchange interaction on superparamagnetic relaxation

H. Kachkachi

Laboratoire de Magnétisme et d'Optique, Université de Versailles St. Quentin 45 av. des Etats-Unis, 78035 Versailles Cedex, France

(Received 21 January 2003; accepted in final form 2 April 2003)

We use Langer's approach to calculate the reaction rate of a system of two (classical) spins interacting via the exchange coupling J in a magnetic field H, with uniaxial anisotropy of constant K. We find a particular value of the exchange coupling, that is $j\equiv J/K = j_{\ab{c}}\equiv 1-h^2$, where $h\equiv H/2K$, which separates two regimes corresponding to a two-stage and one-stage switching. For $j\gg j_{\ab{c}}$ the Néel-Brown result for the one-spin problem is recovered.

05.40.-a - Fluctuation phenomena, random processes, noise, and Brownian motion.
75.50.Tt - Fine-particle systems; nanocrystalline materials.

© EDP Sciences 2003