Surface Instability of Paramagnetic Liquid in Non-uniform Magnetic Field

The manipulation of magnetic fluids by external magnetic field is contactless and free of Joule heating. The paramagnetic liquid offers possibly of manipulation and has a potential application in rare earth element separation. Yet, unlike super-paramagnetic liquid, e.g. ferrofluid, such dynamics is lack of investigation. To observe the combined effect of gravity and magnetic field on paramagnetic solution, the permanent magnet was moved vertically above the free surface of DyCl3 and MnSO4 solution. The change of interface was followed optically by shadowgraph. The focus of the work is the interfacial height difference. Moreover, the morphology of the free interface was observed. The objective one is investigated by changing the concentrations as well as the speed of applying and removing of the magnet. The speed of the moving magnet falls into two categories. One relates to quasi-static magnetization and demagnetization and the second represents jump-like magnetization and demagnetization, i.e. 0.5 mm/s and 20 mm/s respectively. It was found, that the level of liquid is oscillating with specific frequency defined by concentration of solution and is independent of the magnet velocity.