Eur. Phys. J. D 24, 77-80 (2003)
https://doi.org/10.1140/epjd/e2003-00128-3

Model simulations of ground-state and finite-temperature properties of disordered magnetic nanostructures

¹ Laboratoire de Physique Quantique, Université Paul Sabatier, CNRS, 31062 Toulouse, France
² Institut für Theoretische Physik, Freie Universität Berlin, Arnimallee 14, 14195 Berlin, Germany

Corresponding author: ^a gustavo.pastor@irsamc.ups-tlse.fr

Received: 10 September 2002
Published online: 3 July 2003

Abstract

The properties of two-dimensional ensembles of magnetic nanoparticles that interact by magnetic dipole coupling are investigated. The low-temperature magnetic arrangements, the average binding energy E_dip due to dipolar interactions, and its scaling behavior with respect to the particle density C are calculated for different types of structural disorder and particle-size distributions. Many different metastable magnetic states are obtained, which exhibit strong noncollinearities and are reminiscent of a spin-glass behavior. For a given C, increases with increasing disorder of the particle positions. For random distributions at low particle densities , E_dip is dominated by the contributions of short interparticle distances. Thus, it scales as with an unusually small exponent –1. The straightforward scaling of the dipole interaction, , is obtained only for or for nearly periodic ensembles. The finite temperature behavior of these disordered interacting nanomagnets is explored. The specific heat and magnetic susceptibility are calculated by performing Monte Carlo simulations. The onset of long-range magnetic order is discussed. In addition we determine hysteresis loops at finite temperatures and compare the results for different degrees of disorder.