Controlling the Coarsening Dynamics of Ferrogranulate Networks by Means of the Filling Fraction—less is More Susceptible

We are exploring in experiments the aggregation process in a shaken granular mixture of glass and magnetized steel beads, filled in a horizontal vessel. After the shaking amplitude is suddenly decreased, the magnetized beads form a transient network that coarsens in time into compact clusters. Here we investigate how an increased volume fraction ϕ of the granulate accelerates the coarsening, whereas a homogeneous magnetic field B⊥ oriented in vertical direction impedes the emergence and growth of the networks. We explore the coarsening dynamics in the (ϕ,B)-control parameter space, and observe that low filling fractions are more susceptible to an increase of B⊥ than high ones.