2015 年 81 巻 832 号 p. 15-00473
Magneto-rheological properties significantly depend on the formation of aggregates of magnetic particles. In the present study, we focus on a ferromagnetic rod-like particle suspension to discuss the phase change of aggregate structures of magnetic rod-like particles in thermodynamic equilibrium. Hence, we here adopted Monte Carlo method, which is a powerful simulation technique for an equilibrium situation, in order to investigate the dependence of the phase change in aggregate structures on the magnetic field strength, the magnetic particle-particle interaction strength, and so forth. Internal structures of particle aggregates are discussed quantitatively in terms of order parameters. The main results obtained here are summarized as follows. In a weak applied magnetic field, the rod-like particles tend to aggregate to form thick linear chain-like cluster if the magnetic particle-particle interaction is sufficiently large for clusters being formed. The neighboring clusters align in the opposite directions to each other. As the magnetic field is increased, thick chain-like clusters grow and become thicker by absorbing the neighboring clusters that align in the opposite direction to the magnetic field direction. This phase change of aggregates is quantitatively verified in the characteristics of the order parameters.
