title: Experimental investigation of a Brownian ratchet effect in ferrofluids.
abstract: We test experimentally a Brownian ratchet system suggested by Engel [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.
authors.affiliation: Institut für Experimentelle Physik, Fakultät für Naturwissenschaften, Universität Magdeburg, Universitätsplatz 2, D-39106 Magdeburg, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: John
authors.forename: Ralf
authors.initials: R
authors.lastname: Stannarius
mesh_terms: D003198:Computer Simulation; D004058:Diffusion / Q000528:radiation effects*; D004574:Electromagnetic Fields; D004735:Energy Transfer / Q000528:radiation effects; D008956:Models, Chemical; D012996:Solutions / Q000737:chemistry* / Q000528:radiation effects*
chemical_list: D012996:Solutions