Regensburg 2004 – scientific programme

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DY: Dynamik und Statistische Physik

DY 46: Poster

DY 46.78: Poster

Thursday, March 11, 2004, 16:00–18:00, Poster D

Growth rate of amplitudes of surface instabilities in ferrofluids — •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). The more general case is a field, which is tilted towards the normal of the surface of the magnetic liquid. In that case you can observe at first liquid ridges instead of the peaks. Increasing further the magnetic induction a stretched hexagonal pattern of crests is emerging on top of the liquid ridges.

The amplitudes of all these instabilities and their relaxation can be measured 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. 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 compared to a theoretical prediction [1].

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