EQUILIBRIUM SUSCEPTIBILITY OF CONCENTRATED FERROCOLLOIDS: MONTE CARLO SIMULATION

The Monte Carlo method is used to study the influence of the magneto-dipole interaction on a highly concentrated system of solid spheres (magnetic fluids). Some analogous works predict the occurrence of long-range magnetic ordering in such a system. Their common feature is the use of periodic boundary conditions. In this work, the periodic boundary conditions are not imposed on the system. Instead, a model of the permeameter is proposed to exclude demagnetizing fields. The results of simulation with moderate values of the dipole-dipole interaction energy and particle concentration are in good agreement with the reliable analytical models. In the region of highly intensive dipole-dipole interactions, which is the subject of the discussions, the "ferromagnetic" ordering is really possible, but only in the case when the diameter of the simulated cylindrical cell is less than four diameters of the dipole sphere. Since this particular nearly-one-dimensional case is obviously far from any practical use and the moment ordering does not occur at larger cell diameters, it is concluded that the periodic boundary conditions are able to produce the simulation artifact of the second-order "paramagnetic-ferromagnetic" phase transition.