Thermodynamics of finite magnetic two-isomer systems

We use Monte Carlo simulations to investigate the thermodynamical behavior of aggregates consisting of few superparamagnetic particles in a colloidal suspension. The potential energy surface of this classical two-isomer syste m with a stable and a metastable "ring" and "chain" configuration is tunabl e by an external magnetic field and temperature. We determine the complex " phase diagram" of this system and analyze thermodynamically the nature of t he transition between the ring and the chain "phase." (C) 1999 American Ins titute of Physics. [S0021-9606(99)51747-9].