Magnetic wetting transition

We follow the spreading of a magnetic liquid, a non wetting ferrofluid, along a wire. The external control parameter of the spreading length of the fluid is the magnetic field generated by a current travelling through the conducting wire. The spreading length results from a balance between capillary and magnetic forces. For a current threshold, we observe a rapid jump of this length corresponding to a sheath-like coverage of the wire. This magnetic wetting transition is analogous to the wetting transition on a fiber, predicted for a totally wetting fluid in the presence of van der Waals forces. The longer range of magnetic forces leads to a transition at a macroscopic scale. The crossover between micro and macro scales is studied. 1 associated with the Centre National de la Recherche Scientifique