Unknotting of quasi-two-dimensional ferrogranular networks by in-plane homogeneous magnetic fields

TL;DR

This study investigates how in-plane magnetic fields influence the structure and growth of ferrogranular networks in quasi-two-dimensional systems, revealing field-induced unknotting and size modulation of clusters through experiments and simulations.

Contribution

It demonstrates that magnetic fields significantly alter network structures, promoting chain formation and suppressing perpendicular connections, which leads to unknotting and size variation of clusters.

Findings

Magnetic fields favor chain and elongated cluster formation parallel to the field.

Moderate magnetic fields produce larger clusters at intermediate times.

Strong fields limit overall cluster growth at longer times.

Abstract

Our ongoing research addresses, by means of experiments and computer simulations, the aggregation process that takes place in a shaken granular mixture of glass and magnetized steel beads when the shaking amplitude is suddenly decreased. After this quenching, the steel beads form a transient network that coarsens in time into compact clusters, following a viscoelastic phase separation. Here we focus on the quasi-two-dimensional case, analyzing in computer simulation the effects of a magnetic field parallel to the system plane. Our results evidence that the field drastically changes the structure of the forming network: chains and elongated clusters parallel to the field are favored whereas perpendicular connecting structures tend to be supressed, leading to the unknotting of the networks observed at zero field. Importantly, we found that moderate field strengths lead to the formation of larger clusters at intermediate time intervals than in the case of weak and strong fields. Moreover, the latter tend to limit the overall growth of the clusters at longer time scales. These results may be relevant in different systems governed by similar magnetically driven aggregation processes as, for example, in the formation of iron-rich planetesimals in protoplanetary discs or for magnetic separation systems.