Abstract
Above a certain density a granular material jams. This property can be controlledby either tuning a global property, such as the packing fraction or by applying shear strain, or atthe micro-scale by tuning grain shape, inter-particle friction or externally controlled organization.Here, we introduce a novel way to change a local granular property by adding a weak anisotropicmagnetic interaction between particles. We measure the evolution of the pressure, P, and coordinationnumber, Z, for a packing of 2D photo-elastic disks, subject to uniaxial compression.A fraction Rm of the particles have embedded cuboidal magnets. The strength of the magneticinteractions between particles is too weak to have a strong direct effect on P or Z when the systemis jammed. However, the magnetic interactions play an important role in the evolution of latentforce networks when systems containing a large enough fraction of the particles with magnetsare driven through unjammed to jammed states. In this case, a statistically stable network ofmagnetic chains self-organizes before jamming and overlaps with force chains once jamming occurs,strengthening the granular medium. This property opens a novel way to control mechanicalproperties of granular materials.