Magnetic fluids consisting of stable colloidal suspensions of various ferrites have been produced by dispersing the precipitated ferrites in nonpolar solvents such as cyclohexane or kerosene. Prior to dispersing in organic solvents, ferrite powders were coated with oleate ion to the extent of bimolecular adsorption by aqeous reaction and then washed in order to remove the second layer surfactant.
The size of dispersed ferrite colloids was ranged from 100 to 150Å and coarser particles could not be stably dispersed.
It was found that the upper limit of colloid content in the magnetic fluid was about 0.6-0.7 g/ml.
The magnetization of the magnetic fluid was not saturated at 9 kOe field, as a result of super-paramagnetic behavior of the ferrite colloids. It was found that the magnetization of the fluid was depended proportionally on the content of ferrite colloid.