The growth of localized states on the surface of magnetic fluids

By means of a local magnetic perturbation we generate localized states on the surface of a ferrofluid in the bistable regime of the Rosensweig instability. Establishing a magnetic ramp at the edge of the vessel enables us to record the growth of the localized spikes with a high speed camera. From the pictures we extract their growth rate. Under variation of the local induction we find a square-root scaling of the growth rate, which can be understood by a saddle-node bifurcation, induced by the local variation of the magnetic induction.