Regensburg 2004 – wissenschaftliches Programm
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DY: Dynamik und Statistische Physik
DY 11: Ferrofluids
DY 11.6: Vortrag
Montag, 8. März 2004, 11:45–12:00, H3
The dispersions relation of surface waves on ferrofluids - an experimental investigation — •Jan Embs — Universität des Saarlandes, FR 7.3 Technische Physik
The surface of a ferrofluid undergoes a spontaneous instability [1] in a static magnetic field oriented perpendicular to the surface. The new configuration consists of a hexagonal arrangement of peaks, with the critical wave number kc = √ρ g0/σ (ρ mass density, σ surface tension of the ferrofluid and g0 ). This behavior may be understood in terms of the dispersion relation ω02(k) of free surface waves: if the magnetization reaches a certain value, the dispersion relation becomes non-monotonic with a local minimum and an anomalous dispersion branch; when the minimum reaches the ω02=0-axis at k=kc , the so-called Rosensweig instability occurs. In my talk I will show how the anomalous dispersion branch can be measured by generating surface waves due to the Faraday instability. Furthermore it is possible to prepare experimentally situations in which both instabilities occur simultaneously; in these bi-critical situations new and interesting patterns can be observed.
[1] M. D. Cowley, R. E. Rosensweig, J. Fluid. Mech. 30, 671 (1967)