Equilibrium properties of a bidisperse ferrofluid with chain aggregates: theory and computer simulations

In this paper we investigate a bidisperse model ferrofluid, where the aggregates are treated as flexible chains, under the influence of an arbitrary valued external magnetic field. An extensive comparison of the theoretical predictions to the results of the computer simulations is provided. Both magnetostatic properties and structural observables are investigated with the help of the newly developed theoretical approach and molecular dynamic simulations. It is shown that the results of the cluster analysis are very sensitive to the cluster definition. Here we use two different criteria for the particles to be bound: an energy criterion which is slightly different in the theory and simulations due to technical problems, and an entropy criterion which is the same for the molecular dynamics and theoretical model. This enables us to compare qualitatively and quantitatively theoretical and numerical microstructural observables, as well as the macro properties of the bidisperse ferrofluids. Finally, an answer to the question which chain criterion should actually be used is provided in this paper.