(289i) Monte Carlo Simulaitons on the Aggregate Structures in a Supension Composed of Magnetic Cubic Particles on a Material Surface

A magnetic particle suspension has been actively investigated in a various fields such as the fluid engineering, the magnetic material engineering, and the colloid and interface science. In addition, the fields of the biomedical engineering and the environmental resource engineering may be new challenging areas as an application of suspensions composed of magnetic particles. In contrast to the ordinary ferromagnetic rod-like particles, hematite particles have a characteristic feature in that the particles have a significantly weak magnetization, which may be a merit for obtaining a stable suspension in a relatively straightforward manner. In addition to spindle-like hematite particles, modern synthesis technologies enable the generation of disk-like and cube-like hematite particles. In the present study, we concentrate on a suspension composed of magnetic cubic particles on a material surface from the viewpoint of applying a magnetic cubic particle suspension to the development of the technology of surface modification. We here treat a variety of situations of non-equal number of particles with the magnetic moments aligning with the two diagonal directions, i.e., the directions toward and away from the material surface. It is assumed that the cubic particles are magnetized in the diagonal direction of the particle, which may be a typical characteristic of hematite cubic particles. Also, the cubic particles are assumed to move on the surface plane in a quasi-2D system in thermodynamic equilibrium with the face of each cubic particle in contact with the bottom material surface under the situation of a strong gravitational field. Monte Carlo simulations have been performed to obtain the results regarding the characteristics of the aggregates and the order parameters of the system for a variety of situations of the composition ratio of upward and downward particles, the magnetic particle-particle interaction and the magnetic field strength. We summarize the main results that were obtained from Monte Carlo simulations in the following. The regime in the particle aggregates is strongly dependent on the composition ratio of these cubic particles. Specifically, the size of closely-packed aggregates becomes smaller, and thin linear clusters are formed in the situation of a strong magnetic field with decreasing composition ratio. An external magnetic field does not function as more significantly inducing the formation of thick and closely-packed clusters for smaller values of the composition ratio. A decrease in the composition ratio comes to dull the regime change in the particle aggregates for a change in the magnetic particle-particle interaction strength. From these results, we understand that a decrease in the composition ratio leads to a suppression of the growth of large closely-packed clusters, which clearly suggests a possibility that the composition ratio may be used as a technique for controlling the cluster formation and the size of closely-packed clusters of cubic hematite particles in the situation of a strong external magnetic field.