Measurements of ferrofluid surface tension in confined geometry

Two methods of determination of the surface tension at the interface of a magnetic liquid and another fluid, in a confined two-dimensional geometry, are presented. The first is based upon a surface instability under the action of a vertical magnetic field and the second uses the deformation of a magnetic droplet in plane layer under the influence of a horizontal magnetic field. Theoretical calculations and experimental results are presented in both cases. Both determinations lead to comparable values of the surface tension $\ensuremath{\sigma}\ensuremath{\approx}3$ mN ${\mathrm{m}}^{\ensuremath{-}1}$.