Co–Zn ferrite nanoparticles for ferrofluid preparation: Study on magnetic properties

Co–Zn substituted nanoferrites having stoichiometric composition Co 1− x Zn x Fe 2O 4 with x ranging from 0.1 to 0.5 were prepared by chemical coprecipitation method. The precipitated particles were used for the preparation of ferrofluid. Ferrofluids having Co 0.5Zn 0.5Fe 2O 4 particles could be used for the energy conversion application utilizing the magnetically induced convection for thermal dissipation. The final estimated cation contents, agreed with the initial degree of substitution. The powder samples were characterized by XRD, TEM, VSM and Mossbauer studies. The precipitated particles showed single-phase fcc spinel structure for all compositions of zinc. The magnetic parameters such as M s, H c, M r, T c and particle size were found to decrease with the increase in zinc substitution. In the case of particles with higher zinc concentration, both ferrimagnetic nanoparticles and particles exhibiting superparamagnetic behavior were present. The fine particles were suitably dispersed in heptane using oleic acid as the surfactant. Volatile nature of the carrier chosen helped in altering the number concentration of the magnetic particles in a ferrofluid.