Phase transitions of granular disks with a magnetic dipole

Abstract

We present a simple experiment to study phase transitions of a granular system composed of disks with a magnetic dipole. The particles are contained within a cylindrical container and are excited through alternating magnetic fields. The initial configuration of this system is a low-density isotropic phase. By increasing the density, a critical value is reached and the system starts to organize into columns. At higher densities an ordered state is obtained where structural columnar patterns are formed. The set up of the experimental device is very easy to implement, using standard high-school and undergraduate physics laboratory facilities. The experiment can be used, combined with computer simulations, to introduce the subject of phase transitions in complex materials.