Flow regimes for a magnetic suspension under a rotating magnetic field

2014 We have performed qualitative observations of both macroscopic and local motions in a ferrofluid and in a suspension of magnetic grains under a rotating magnetic field H. The individual grains rotate synchronously. We then find that : 2014 When the macroscopic magnetization vector M is uniform over the whole sample volume, there is no bulk rotation of the liquid. 2014 Slight departures from uniformity are enough to induce asynchronous rotations of the liquid of either sign, depending on the distribution of magnetic poles in the sample. 2014 Large departures from uniformity and powerful bulk rotations can be imposed very easily either by inhomogeneous static fields or grain concentrations. LE JOURNAL DE PHYSIQUE TOME 34, FÉVRIER-MARS 1973,