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DY: Dynamik und Statistische Physik

DY 33: Ferrofluids and Liquid Crystals

DY 33.2: Vortrag

Montag, 7. März 2005, 14:15–14:30, TU H2032

Comparing measurements of the growth rate of the Rosensweig instability with theoretical predictions — •Holger Knieling, Reinhard Richter, and Ingo Rehberg — Universität Bayreuth, Lehrstuhl Experimentalphysik V, 95440 Bayreuth

The surface of magnetic fluids subjected to a normal magnetic field is becoming unstable when a certain threshold of the magnetic induction is surpassed and the initially flat surface exhibits a stationary array of peaks (Rosensweig or normal field instability). Up to now there exists only a theoretical prediction of the behaviour of the growth rate of this surface instability [1]. Therefore we have performed time resolved measurements of the amplitude and their relaxation with the help of a linear array of 32 Hall sensors which are placed directly under the ferrofluid. Sensors situated under a ridge (trough) detect higher (lower) values of the local magnetic induction, respectively. By calibrating the magnetic signal with normed reliefs of the ferrofluid surface the height of the liquid surface can be measured as well. With a time resolution of the sensors of about a half millisecond the maximal growth rate of the modes of the Rosensweig instability can be measured and are compared with the theoretical predictions.

[1] A. Lange, Europhys. Lett., 55 (3), 327-333 (2001)