Aggregation of Magnetic Microspheres: Experiments and Simulations

Uniformly sized microspheres interacting via long-range magnetic dipolar forces are used to study diffusion-limited cluster aggregation in a plane. The results show that it is possible to scale the temporal evolution of the cluster size distribution and that there is a crossover in fractal dimension from $D=1.52\mathrm{}\pm 0.05$ to $D=1.16\mathrm{}\pm 0.05$ in the limit of weak and strong dipolar coupling. External magnetic fields are shown to produce pronounced chaining with $D$ approaching 1. The results compare favorably with computer simulations of aggregation of the same type of particles.