Eur. Phys. J. B 45, 369-375 (2005)
https://doi.org/10.1140/epjb/e2005-00186-3

Ordered systems of ultrafine ferromagnetic particles

Institut für Festkörperphysik, Technische Universität Darmstadt, Hochschulstr. 8, 64289 Darmstadt, Germany

Corresponding author: ^a porto@fkp.tu-darmstadt.de

Received: 22 July 2004
Revised: 3 January 2005
Published online: 6 July 2005

Abstract

A simple model for systems of dipolarly interacting single-domain ultrafine ferromagnetic particles is studied by Monte Carlo simulations. Zero field cooling and field cooling as well as relaxation experiments are used to compare systems with positional and orientational disorder to systems which are (i) positionally, (ii) orientationally, and (iii) positionally and orientationally ordered. It is shown that, as far as macroscopic observables are concerned, these partially [cases (i) and (ii)] or fully [case (iii)] ordered systems, despite quantitative differences, behave qualitatively very similar to the disordered one. This holds true even for the relaxation, where the decay of the magnetization (measured in units of the saturation magnetization ) leads to an instantaneous relaxation rate vanishing as a power-law as a function of time t, . The exponent n is found to increase with increasing concentration, and becomes n > 1 for dense systems.