Internal motion due to the spinning particles in the magnetic liquid droplets in an alternating magnetic field

A. Cebers¹ - G. Bossis²

¹ Institute of Physics, Latvian University, Salaspils-1, LV-2169, Latvia
² LPMC CNRS U.M.R. 6622, Universite de Nice-Sophia Antinopolis, Parc Valrose 06108 Nice, Cedex 2, France

Abstract
Finite magnetisation relaxation time effects under the action of the long-range magnetic interaction forces are considered. In the case of the pair of magnetising particles it is shown by the direct calculation that the right expression for the torque causing relative motion of the magnetic particles could be obtained from energetical approach if the dependence of the dissipation rate on the velocity of the motion is accounted for. By comparison of the expressions for the total and orbital torque’s the torque causing the spinning of the particles is predicted. Similar phenomena take place in the case of ellipsoidal droplet oriented under the arbitrary angle to the external alternating magnetic field direction. The existence of antisymmetric viscous stresses is shown for that case and internal circulation arising due to the spinning particles is calculated by the virial method. As situation easy for the experimental study of those effects the flow in plane layer of magnetic fluid in the direction of the inclination of the alternating magnetic field is predicted. From the cases considered the general rule concerning the direction of the internal flow arising due to the spinning particles in unidirectional alternating magnetic field is formulated - internal circulation arises in the direction of the deviation of the symmetry axis of the system from the external alternating field direction. From comparison of this rule with the observations of internal circulation in inclined to alternating electric field agglomerates of the particles in the different colloidal solutions it is concluded that those effects are not caused by finite polarization relaxation time effects. Table 1, Figs 6, Refs 15.