We have investigated aggregation phenomena of ferromagnetic colloidal dispersions composed of rod-like hematite particles which have a magnetic moment normal to the particle axis, by means of the cluster-moving Monte Carlo method. In concrete, we have treated a two-dimensional dispersion in order to clarify the influences of the particle aspect ratio, magnetic interactions between particles, and the magnetic field strength on particle aggregations. Internal structures of particle aggregates have been discussed quantitatively in terms of radial distribution, pair correlation, orientational pair correlation functions, and number distributions of clusters. The results obtained here are summarized as follows. Rod-like particles tend to aggregate to form raft-like clusters more significantly along the magnetic moment direction as magnetic particle-particle interactions increase. However, such raft-like clusters do not aggregate further to form thicker clusters, which is in significantly contrast to dispersions of spherical or rod-like particles with a magnetic moment along the particle axis.
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