A single peak of the Rosensweig instability

A single peak formed on the free surface of a ferrofluid subject to an overcritical magnetic field is investigated both theoretically and experimentally with respect to its static and dynamic properties. Using a pertubation analysis up to fifth order in the surface deflection the static profile of the surface in the non-linear regime is obtained for the one-dimensional situation. If the static magnetic field is superimposed with an oscillating part an intricate pattern of subharmonic response of the peak is found experimentally. A simple, analytically tractable model is introduced which displays qualitative agreement with the experimental results.