Formation and Kinetics of Self-Assembled Structures of Magnetic Microparticles in Rotating Fields

We study the formation of self-assembled structures of magnetic microparticles subjected to the action of a biaxial alternating field. The used device comprises a set of two nested orthogonal Helmholtz coils that can produce rotating fields in the horizontal plane by applying proper alternating currents to the coils. In this way, it is possible to induce a planar organization in a set of magnetic micrometer-size Fe and Ni particles dispersed in a liquid. We investigate, by means of video-microscopy image analysis performed in the MATLAB environment, the time evolution of topological parameters, as the number of objects detected. We also investigate the circularity of the dominant object at different stages of the structure formation and the region of power-law behavior of the time evolution. We compare the characteristic times for pattern formation under different field configurations.