We have experimentally investigated the influence of a magnetic interaction between the grains on the flow of a granular material in a rotating drum.
The magnetic cohesion is induced by applying a homogeneous external magnetic field →B
oriented either parallel or perpendicular to the gravity →g.
The drum rotating speed has been selected to obtain a continuous flow when the magnetic field is switched off.
We show that, for both magnetic field orientations, the cohesion is able to induce a transition
between the continuous flow regime to the discrete avalanche regime.
The avalanche dynamics is periodic when →B⊥→g and irregular when →B∥→g.
Moreover, the maximal angle of stability θm increases strongly with the cohesion strength and could be higher than 90° when →B⊥→g.
A toy model based on the stability of a magnetic block on a magnetic inclined plane is proposed to explain this behavior.