Formation kinetics of magnetic chains, rings, X's, and Y's

The kinetics of aggregation in a monolayer of magnetic particles are studied using stochastic dynamics computer simulations. At low densities (<8% coverage) the equilibrium structure is made up of chains and rings; the primary mechanisms by which these motifs form are described. At higher densities (>15% coverage), we observe large transient concentrations of Y-shaped and X-shaped defects that ultimately give way to an extended, labyrinthine network. Our results suggest that a defect mechanism -- such as that proposed by Tlusty and Safran, Science 290, 1328 (2000) -- could drive a metastable phase separation in two dimensions.