Structural Analysis of Self-Assembled Lattice Structures Composed of Cubic Hematite Particles

The structural analysis of self-assembled layers with lattice-like structures composed of cubic hematite particles with a side length of approximately 0.9 mu m was carried out by means of radial distribution functions (RDFs). The cubic particles were synthesized by aging a solution of FeCl3 for 8 days at 373 K. The RDFs were determined by a digital image analysis method from direct optical microscope observation of the particles. Two-dimensional (2D) Monte Carlo simulations of the cubic hematite particles were also carried out to clarify the influences of a magnetic field on the lattice structure. In very weak geomagnetic fields, clusters with square lattice structures are formed on a glass plate through the particle sedimentation process. It is clear from the simulation results that the square lattice structures are stabilized by the closed orientation of the magnetic moments of the particles. A broack houlder appeared at a slightly longer distance from the first peak position in the experimental RDF for relatively strong magnetic fields, corresponding to the two split small peaks that appeared in the simulated RDF for an ideal monodisperse system, suggesting that oblique lattice structures with magnetic moments aligned to the field direction are formed to minimize the magnetic potential energy.