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Experimental investigation of a Brownian ratchet effect in ferrofluids
Phys. Rev. E 80, 050104(R) – Published 25 November, 2009
DOI: https://doi.org/10.1103/PhysRevE.80.050104
Abstract
We test experimentally a Brownian ratchet system suggested by Engel et al. [Phys. Rev. Lett. 91, 060602 (2003)]. This ratchet system is based on a magnetic fluid that contains nanometer sized magnetic particles in a thermal bath of carrier fluid. An external static magnetic field and, perpendicular to it, an oscillatory magnetic field act on the ferrofluid particles; the total magnetic field contains no rotating component. The directed effective rotation of the particles due to the ratchet effect induces a macroscopic torque density of the fluid. The torque on a spherical ferrofluid sample is measured in dependence on the field parameters. A quantitative comparison with predictions from a microscopic and a phenomenological model are given. Both models describe certain aspects of the measurements correctly, but qualitative discrepancies between both models and experiment are found, particularly in the high-frequency range.
Article Text
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