Regensburg 2007 – wissenschaftliches Programm

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DY: Fachverband Dynamik und Statistische Physik

DY 26: Ferrofluids / Liquid crystals

DY 26.7: Vortrag

Donnerstag, 29. März 2007, 12:00–12:15, H3

Role of interactions in ferroluid thermal ratchets — •Volker Becker — Charite, Augustenburger Platz 1, 13353 Berlin

Orientational fluctuations of colloidal particles with magnetic moments may be rectified with the help of external magnetic fields with suitably chosen time dependence [1]. As a result a noise-driven rotation of particles occours giving rise to a macroscopic torque per volume of the carrier liquid. We have theoretically analyzed the influence of mutual interactions between the particles on this ratchet effect by studying a model system with mean-field interactions. The stochastic dynamik may be described by a nonlinear Fokker-Planck equation for the collective orientation of the particles which we have solved aproximately. We have found that interactions favouring the parallel alignment of the magnetization of the ferrofluid particles reinforce the ratchet effect. Morover we have determined an intevall for the ratio between coupling strength and noise intensity for which a self-sustained rectification of fluctuations can be observed. The ratchet effect then operates under conditions for which it where impossible in the absence of fluctuations.

[1] A. Engel, H. W. Müller, P. Reimann, A. Jung, Phys. Rev. Lett. 91, 060602(2003); A. Engel, P. Reimann, Phys. Rev. E 70, 051107 (2004)

[2] V. Becker, A.Engel, cond. Mat./0609546