Effects of the magnetodipolar interactions in the alternating magnetic fields

A macroscopic theory for the description of the structure formation in a sy stem of magnetic dipoles under the action of a high-frequency rotating held is presented. Continuum equations for the effective magnetic field strengt h describing particle interactions are derived. It is shown that, contrary to the case of a constant magnetic field, where the demagnetizing held aris ing from a concentration fluctuation stabilizes the system with respect to the phase separation, the same concentration fluctuation will be amplified in the case of a rotating magnetic field, lending to the formation of a lay ered structure. The extensions of the model necessary for the description o f the formation of the periodic structures in the rotating field are consid ered and the relevance of the present model for the explanation of phase se paration in shear flows of magnetorheological suspensions is indicated. (C) 1999 Elsevier Science B.V. All rights reserved.