Dresden 2009 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 20: Focus: Magnetic Soft Matter II

CPP 20.8: Talk

Wednesday, March 25, 2009, 12:00–12:15, ZEU 222

Brownian ratchet effect in a ferrofluid sample — •Thomas John and Ralf Stannarius — Otto-von-Guericke-Universität Magdeburg, Germany

We investigate experimentally a Brownian ratchet system suggested by Engel et al. [1]. The Brownian ratchet system is based on a magnetic fluid which contains nanometer sized magnetic particles in a thermal bath of carrier fluid. An external static and perpendicular a temporal asymmetric oscillatory magnetic field acts on the particles. Depending on the parameter of this non-rotating field on a spherical ferrofluid sample the induced macroscopic torque is measured. A quantitative comparison of measured torques with predictions from a microscopic [2] and a phenomenological model from M. I. Shliomis [3] are given. Both models describe certain aspects of the measurements only in limited parameter ranges. Several qualitative discrepancies between these models and experiment are found.

[1] A. Engel et al., Phys. Rev. Lett. 91, 060602 (2003).

[2] A. Engel et al., Phys. Rev. E 70, 051107 (2004).

[3] M. I. Shliomis, Phys. Rev. Lett. 92, 188901 (2004).