Berlin 2012 – wissenschaftliches Programm

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 28: Colloids and Complex Liquids I

CPP 28.5: Vortrag

Mittwoch, 28. März 2012, 16:15–16:30, C 130

Core size effects on the rotation and stability of dipolar clusters in rotating magnetic field — •Ayan Ray and Thomas M. Fischer — Institut für Experimentalphysik, Universität Bayreuth, 95440 Bayreuth, Germany.

We report on the rotation of colloidal clusters of non magnetic holes and of mixtures of paramagnetic beads with non magnetic holes in a ferrofluid in a rotating external magnetic field. The precession angle of the external field is a control parameter determining the stability of the cluster. Clusters become locally unstable when the local precession angle reaches the magic angle. Cluster shape dependant depolarization fields lead to a deviation of the local from the external precession angle such that close to the external magic angle different cluster shapes might coexist. For this reason cluster transitions are weakly or strongly first order transitions. If the transition is weakly first order a critical speeding up of the cluster rotation is observed. No speeding up occurs for strongly first order cluster transitions with hysteresis. The strength of the first order transition is controlled by the size of the core of the cluster.