  Non-equilibrium structure formation and conversion of spinning to
translational motion of magnetic colloids driven by an external rotating
magnetic field in microchannels is studied by particle-based mesoscale
hydrodynamics simulations. For straight channels, laning is found. In ring
channels, the channel curvature breaks symmetry and leads to a net fluid
transport around the annulus with the same rotational direction as the
colloidal spinning direction. The dependence of the translational velocity on
channel width, ring radius, colloid concentration, and thermal motion is
predicted.
