Break-up of dipolar rings under an external magnetic field

An experimental and theoretical study of the deformation and break-up process of rings, formed by magnetic microspheres, under the application of an external magnetic field is reported in this Letter. When the external magnetic field is applied parallel to the plane of the rings, we found that the break-up process has three different outcomes depending on the way of application and time history of the external held: (a) deformation into a compact set of dipoles with a triangular lattice structure, (b) opening into a single chain, and (c) break-up into two chains with various relative sizes. A thorough theoretical investigation of the breakup process has been carried out based on computer simulations, taking into account solely the dipole-dipole and dipole-external field interactions, without thermal noise. The experimental results and the simulations are in good agreement. (C) 2000 Elsevier Science B.V. All rights reserved.