Dipolar gels formed by aggregation of magnetized beads

The out-of-equilibrium aggregation of dipolar particles, such as magnetized beads, leads to the formation of large structures composed of chains, loops, and eventually ribbons. In the present study, we focus on the evolution of these different substructures in a two-dimensional system confined within progressively shrinking environments. Using numerical simulations, we identify structural events as a function of the packing fraction. At low density, a percolation threshold 𝜙𝑝≈0.15 is evidenced, where chainlike structures merge into a single large aggregate with significant voids. This gel-like structure then densifies as 𝜙 increases. At large 𝜙 values, crystallites of both square and hexagonal order phase appear, but they are far from extending over the whole system.