Non-ergodic tube structures in magnetic gels and suspensions.

We present results of a study of internal structures, which can appear in magnetic suspensions and gels filling a flat gap under the influence of a magnetic field applied perpendicular to the gap walls. The considered system consists of magnetizable microparticles with a mean diameter of ∼35 μm. Experimental observation demonstrates that the particles can form stable tube shaped structures elongated along the field direction. These structures have internal cavities. The theoretical analysis, performed in this study, shows that the tubes do not correspond to a thermodynamic equilibrium state of the system and rather present transitive non-ergodic structures. These structures are stacked in a state of local energetic minima because of the relatively large size of the particles and negligible Brownian effects. Our theoretical model is suggested to explain the physical reason of the appearance of tube-like structures.