Nonequilibrium cluster structures formed in a thin magnetorheological fluid layer subjected to a dc magnetic field

We experimentally investigate cluster structures formed by paramagnetic particles in a thin magnetorheological (MR) fluid layer, the thickness of which normalized by the particle diameter ranges from 3.8 to 31, under a dc magnetic field perpendicular to the fluid layer. We particularly focus on cluster structures formed in a dc magnetic field of high ramping rates, in which case the structures may be greatly different from those formed under equilibrium conditions. When a dc magnetic field is applied so rapidly, paramagnetic particles form chain clusters along the field direction as expected, but some chain clusters coalesce in the lateral direction to form bent-wall structures. We analyze the dependence of cluster structures on experimental parameters such as the thickness of the MR fluid layer and the intensity of the magnetic field.