Large-Scale Directional Motion By Symmetry Breaking in Active Magnetic Suspensions

We investigate transitions to collective dynamics in a system of self-propelled magnetic swimmers in a Newtonian fluid. Using tools from kinetic theory, we develop a coarse-grained continuum model that accounts for magnetic interactions and is amenable to a stability analysis and numerical simulations. Using this model, we uncover a symmetry breaking transition in which long-range dipolar interactions can give rise, for certain types of swimmers, to large-scale orientational order in the plane of motion with a net uni-directional particle flow in an arbitrary direction. By exploring the parameter space, we investigate the order-to-disorder transition and obtain a phase diagram as a function of magnetic flux, number density, and diffusivity.