Regensburg 2004 – wissenschaftliches Programm
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DY: Dynamik und Statistische Physik
DY 46: Poster
DY 46.76: Poster
Donnerstag, 11. März 2004, 16:00–18:00, Poster D
Examination of the magnetisation dynamics of rotating ferrofluids — •Sonia May1,2,3, Jan Embs1,2, Christian Wagner1, Klaus Knorr1, and Manfred Lücke2 — 1Technische Physik, Universität des Saarlandes — 2Theoretische Physik, Universität des Saarlandes — 3Department of Physics, University of Hull
Ferrofluids are colloidal suspensions of nanometre sized magnetic particles in a magnetically inert liquid which, being coated by polymeric surfactants do not agglomerate. External magnetic fields exert forces and torques on the particles that are transmitted via viscous friction on the ferrofluid as a whole. In equilibrium ferrofluids show (super) paramagnetic behaviour in a magnetic field H with magnetisation M and field H being parallel to each other.
Under non-equilibrium conditions where the ferrofluid rotates M and H are no longer parallel to each other. For such situations various theoretical models for the dynamic magnetisation equation have been proposed that are not yet properly tested; in particular in regimes where the (local) vorticity Ω is comparable to or larger than the Brownian rotational relaxation rate 1/τ.
Experiments have been performed on ferrofluids rotating with constant frequency Ω. The magnetisation component normal to the applied field is measured using a Hall sensor as a function of applied fields of up to 60 kA/m and as a function of rotational frequencies of up to 2,500 rad/s.
Experimental results for the non-equilibrium situation are compared with theoretical models.