Surface waves in ferrofluids under vertical magnetic field (original) (raw)

We present here new experimental results about the waves at the horizontal free surface of a magnetic fluid submitted to a normal magnetic field. The waves are generated by a small modulation at frequency ω of the vertical field H e . Using a shadowgraph method, we are able to measure the wavevector k of the 2D waves for a given value of ω and H e . The dispersion relation of the surface waves is established experimentally. On the other hand, we propose a theoretical derivation of the dispersion equation which includes a more complete treatment of the magnetic term than the previous works. Finally, we conclude that a linear and inviscid analysis is sufficient to fit well the experimental data, except in the vicinity of the critical field where a surface instability occurs. PACS. 75.50.Mm Magnetic liquids -47.35.+i Hydrodynamic waves -68.10.-m Fluid surfaces and fluid-fluid interface