As a senior thesis project Anitra Novy investigated a homogenized ferrofluid film spread onto a water surface. Panel A above shows flat ferrofluid droplets spread evenly on the water surface. Panel B shows the reaction of this film to a bar magnet held a few centimeters above the surface of the film. The film is repelled by the magnet and collects in a ring of finite radius as shown in panel C. In time ferrofluid droplets shoot from this ring (e.g. 2 oclock, panel C) to the center, where they form a crystal lattice. The question Anitras thesis answered was, How can you have it both ways? How can the ferrofluid be attracted and repelled by a magnet at the same time? Published in the American Journal of Physics.
Patterns in a Ferrofluid