Oscillatory surface deformation of paramagnetic rare earth solutions driven by an inhomogeneous magnetic field

The deformation of the free surface of a paramagnetic liquid subjected to a non-uniform magnetic field has been studied. A transient deformation of the surface caused by the interplay of gravity, magnetic field and surface tension is observed when a permanent magnet is moved vertically downwards to the free surface of the liquid. Different concentrations of rare-earth metal salt (DyCl 3 ) were used and different magnet velocities were studied. The deformation of the interface was followed optically by means of a microscope and recorded with a high-speed camera. The experimental results are compared and discussed with complementary numerical simulations. Detailed results are given for the static shape of the deformed surface and the temporal evolution of the surface deformation below the center of the magnet. The frequency of the surface oscillations is found to depend on the concentration of the salt and is compared with analytical findings. Finally, a potential application of the effects observed is presented.