Magnetic properties and structure of polydisperse ferrofluid models

The influence of polydispersity on the equilibrium properties of dipolar systems with short range repulsive interactions (modeled by a shifted and truncated Lennard-Jones pair potential) is studied by means of canonical Monte Carlo simulation and a high field approximation perturbation theory. The particle concentrations and the average magnetic moments of the investigated systems are typical of real ferrofluids. The magnetization curves are calculated and the microstructures are analyzed as a function of density, and the obtained results are compared with the data determined in the monodisperse equivalents of the systems. At weak and moderate magnetic fields the magnetization is found to be generally higher in the polydisperse system than in the corresponding monodisperse one. Our findings for the magnetic properties can partly be explained by the structural characteristics obtained from the simulations.