A magnetic fluid for operation in strong gradient fields

The properties of a magnetic fluid based on colloidal magnetite and VM-3 vacuum oil have been experimentally studied. The fluid is designed for a long-term operation in strong gradient magnetic fields. A variant of magneto-granulometric analysis has been proposed that makes it possible to determine the average magnetic moment, variance of magnetic moments, and number density of particles with no a priori assumptions of the particle size distribution. Magneto-granulometric and cluster analyses of the magnetic fluid have been carried out. It has been shown that individual particles with an average diameter of the magnetic core of 7 nm, which is markedly smaller than those in common commercial fluids, prevail in the studied solution. The volume concentration of multiparticle clusters is also low; their total contribution to the initial magnetic susceptibility of the fluid only slightly exceeds 3%. The small particle sizes and the low cluster concentration provide the colloidal solution with a high stability in a strong magnetic field and a centrifugal force field at a rather high saturation magnetization of the solution.