Response of a ferrofluid to traveling-stripe forcing

TL;DR

This study investigates how a ferrofluid's surface waves respond to a traveling magnetic modulation, revealing controllable wave properties and resonance phenomena that help determine the critical conditions for instability.

Contribution

It introduces a method to excite and control ferrofluid surface waves using traveling magnetic fields, providing insights into wave dispersion and instability thresholds.

Findings

Wave wavelength and velocity are controllable via magnetic modulation.

Resonance behavior similar to harmonic oscillators is observed.

Critical magnetic field for instability is estimated from wave dispersion.

Abstract

We observe the dynamics of waves propagating on the surface of a ferrofluid under the influence of a spatially and temporarily modulated field. In particular, we excite plane waves by a travelling lamellar modulation of the magnetization. By this external driving both the wavelength and the propagation velocity of the waves can be controlled. The amplitude of the excited waves exhibits a resonance phenomenon similar to that of a forced harmonic oscillator. Its analysis reveals the dispersion relation of the free surface waves, from which the critical magnetic field for the onset of the Rosensweig instability can be extrapolated.