Dresden 2006 – scientific programme

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DY: Dynamik und Statistische Physik

DY 46: Poster

DY 46.12: Poster

Thursday, March 30, 2006, 16:00–18:00, P1

Thermal ratchet e ect in ferrofluids with mean-field interactions — •Volker Becker and Andreas Engel — Carl-von-Ossietzky-Universität, 26111 Oldenburg

Ferrofluids are suspensions of magnetic particles in an suitable carrier fluid.A thermal ratchet system for ferrofluids was introduced in [1]. Under the influence of a suitable time dependent magnetic field, rectification of orientation fluctuations of the magnetic grains become possible. The magnetic grains was modelled in [1] as non-interacting overdamped particles with frozen magnetic moments. To go beyond the the one particle approach we propose a simple model taking into account the interactions between the orientations of the magnetic grains. To keep things simple we consider a mean-field like attractive coupling between the orientations. It is possible to derive a mean-field Fokker-Planck equation for the orientation density. This equation has a similar form as one in the single particle approach, however with an self-consistently effective magnetic field. We study the influence of the particle interactions and in particular investigate whether the ratchet effect in many-particle systems may operate even with time choices of the time dependent fields which induce no ratchet effect in the single particle approach.

[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)