Characterization of different magnetite-cobalt nanoparticles in hydrocarbon-based magnetic fluids by means of static and dynamic magnetization measurements

Magnetic nanoparticles with different compositions (Co x Fe3-x O4, 0≤x≤0.1) were synthesized from metal salts using a coprecipitation technique to produce magnetic fluids following a peptization technique. The liquid carrier was the hydrocarbon Isopar M and the surfactant was oleic acid. The colloidal-sized ferrimagnetic nanoparticles produced were found to be superparamagnetic. Measurements of the complex magnetic susceptibility were carried out to evaluate the resonant frequency f res, the anisotropy constant K, and anisotropy field H A. f res was found to be a linear function of the cobalt content of the magnetic nanoparticles over the range of cobalt content studied