Effect of electric and magnetic fields on the magnetic susceptibility of a magnetic colloid containing magnetized aggregates

Abstract

The results of experimental studies on the magnetic susceptibility of a magnetic colloid containing magnetized aggregates under the action of external electric and magnetic fields are presented. The magnetic susceptibility was determined using the bridge method at a frequency of 320 Hz; observations and analysis of structural changes in the colloid were carried out with an optical microscope. It is shown that under the action of weak electric fields, insufficient for the development of electrohydrodynamic flows, a preferential orientation of small anisotropic aggregates along the electric field strength occurs, leading to a decrease in magnetic susceptibility. It was found that under the action of stronger electric fields, significant changes in the structural state of the system occur – the formation of rope-like structures elongated along the measuring magnetic field and, as a consequence, the magnetic susceptibility increases. A further increase in the electric field leads to the breakup of structural formations into smaller ones and to a change in the dependence of the magnetic susceptibility of such media on the strength of both the electric and the additional magnetic field. The discussion of the obtained results was based on the structural changes occurring in the aggregate system as a result of the action of electric and magnetic fields.