The interfacial stability of a ferromagnetic fluid

Abstract

A normal magnetic field has a destabilizing influence on a flat interface between a magnetizable and a non-magnetic fluid. Stabilizing influences are provided by interfacial tension and gravity if the lighter fluid is uppermost. The critical level of magnetization for onset of the instability is derived for a fluid having a non-linear relation between magnetization and magnetic induction. Experiments using a magnetizable fluid, which contains a colloidal suspension of ferromagnetic particles, at interfaces with air and water are made and cover a wide range of density differences. Measurements confirm the prediction for critical magnetization, and it was found that, after onset, the interface took a new form in which the elevation had a regular hexagonal pattern. The pattern was highly stable, and the measured spacing of peaks agreed reasonably with that derived from the critical wave-number for the instability of a flat interface.

Ferrofluid drops in rotating magnetic fields

“…4 Oe peaks start to develop at the periphery of the drop. They are a manifestation of the normal-field or Rosensweig instability [11,17]. The shape of the drop is now rather complicated and appears to be non-stationary.…”

“…For both small and large magnetic fields an oblate spheroid was found to be the stationary shape of the drop. For large fields the spheroid is crowned by peaks at the periphery which are due to the normal field instability [11,17] and induce a 'spiny starfish' appearance. For intermediate values of the magnetic field various transient shapes were found.…”

Rosensweig instability in ferrofluids

“…When a layer of such a liquid is subjected to a vertically oriented and uniform magnetic field, above a critical value of the field strength a pattern of periodic peaks appears on the surface of the liquid. This is the classical Rosensweig instability observed long ago by Cowley and Rosensweig [1]. Physics behind the Rosensweig instability is related to a feed back from the ferrofluid to the applied magnetic field.…”

Mag(net)ic Liquid Mountains

“…1). is pattern-forming instability has been reported by Cowley & Rosensweig [2] soon aer the synthesis of the first ferrofluids. Measuring the topography by means of X-rays X-rays which are penetrating spikes are more attenuated than those trespassing troughs of the pattern.…”