Résumé
We use Monte Carlo simulations to investigate the thermodynamical behaviour
of aggregates consisting of few superparamagnetic particles in a colloidal
suspension. The potential energy surface of this classical two-level system
with a stable and a metastable `ring' and `chain' configuration is tunable by
an external magnetic field and temperature. We determine the complex `phase
diagram' of this intriguing system and analyze thermodynamically the nature of
the transition between the ring and the chain `phase'.