Self-assembling of non-Brownian magnetized spheres

If we pour spherical beads in a container and then gently shake it to increase the compaction of the system, the packing fraction will converge logarithmically to 0.64, the density of a random close packing. If the system is specially sheared, or tapped through an annealing procedure, lattices may self-organize. In this work we study granular crystallization induced by magnetic cohesion. We observe an interesting granular polymorphism probably due to an effective van der Waals-like interaction.