Rayleigh-Taylor instability with magnetic fluids: Experiment and theory

We present experiments showing the Rayleigh-Taylor instability at the inter face between a dense magnetic liquid and an immiscible less dense liquid. T he liquids are confined in a Hele-Shaw cell and a magnetic field is applied perpendicular to the cell. We measure the wavelength and the growth rate a t the onset of the instability as a function of the external magnetic field . The wavelength decreases as the field increases. The amplitude of the int erface deformation grows exponentially with time in the early stage, and th e growth rate is an increasing function of the field. These results are com pared to theoretical predictions given in the framework of linear stability analysis.