COMPETITION BETWEEN THE BENARD-MARANGONI AND THE ROSENSWEIG INSTABILITY IN MAGNETIC FLUIDS

The linear stability analysis of a layer of a magnetic fluid with a de formable free surface, which is heated from below and exposed to a uni form, vertically applied magnetic field is presented. In this configur ation the temperature dependence of the surface tension, the buoyancy and the focusing of the magnetic field due to surface fluctuations act as destabilising effects. We show that this system has for thin layer s a stationary codimension-2-point, which can be reached for experimen tally relevant values of the material parameters. We also analyse the transition from thin to thicker layers for which there is no codimensi on-2-point and we show how the codimension-2-point disappears. Finally we demonstrate that there is no oscillatory instability in the region s of parameter space considered here.