Magneto-rheological properties of a magnetic particle suspension are strongly dependent on the formation of aggregates of magnetic particles. A suspension of ferromagnetic rod-like particles can be expected to exhibit strong magneto-rheological characteristics, which is a significantly important factor for application of magnetic particle suspensions to mechanical dampers and actuators. Hence, in the present study, we address a suspension composed of ferromagnetic rod-like particles in thermodynamic equilibrium. Monte Carlo simulations have been carried out in order to investigate the dependence of the phase change hi aggregate structures on the magnetic field strength for various cases of the magnetic particle-particle interaction strength. The cluster formation of magnetic particles significantly appears for a strong magnetic interaction larger than a certain value. As the applied magnetic field strength is increased, the clusters come to dissociate into small clusters, and finally at a certain strong applied magnetic field, all clusters completely dissociate into single-moving particles. This clearly exhibits that an applied magnetic field induces the phase change in a magnetic rod-like particle suspension.
