Friday,
September 28, 2007 - 4:00 P.M., NSH 184
Large ensembles of interacting particles subject to an external forcing often exhibit unexpected nontrivial collective behaviors. Pattern formation and novel collective dynamics in sub-monolayers of magnetic microparticles subject to external alternating electromagnetic fields will be discussed. Depending on the excitation parameters a rich variety of structures such as clusters, rings, chains and networks can be generated in the sub-monolayer of magnetic particles on the flat solid surface. Remarkable nontrivially ordered dynamic self-assembled structures ("magnetic snakes") are formed in the ensemble of magnetic microparticles suspended on the liquid/air interface in a certain range of excitation parameters. These structures emerge as a result of the competition between magnetic and hydrodynamic forces. The birth and existence of the “snake” is driven by pattern induced waves on the water surface. Strong induced vortex flows on the surface of water finalize the rich hydrodynamic picture of the “magnetic snake”. Self-assembled snakes have a complex magnetic ordering. The segments of the snake exhibit long-range antiferromagnetic ordering mediated by the surface waves, while each segment is composed of ferromagnetically aligned chains of microparticles. The mechanism of the pattern formation and nontrivial magnetic properties of the generated dynamic self-organized patterns will be discussed.