Synthesis of Co0.5Ni0.5Fe2O4 Nanoparticles by microemulsion route and effect of size and morphology on magnetic properties

In the present study, Co0.5Ni0.5Fe2O4 nanoparticles were synthesized using reverse microemulsion route and water/CTAB/1-hexanol system. The effect of size and morphology was investigated on magnetic properties. For this purpose, the experiments were done in 7 steps which they were selected based on stability range of ternary diagram of water/CTAB/1-hexanol. Such configuration was chose pursuant to the different ratios of water/CTAB/1-hexanol with constant amount of metal salts in each experiment. The results showed that by changing the microemulsion composition the size and morphology can change. It was observed that for more surfactant to water ratio the morphology changed from spherical to flake due to the decrease in surface tension. For surfactant to water ratios of 2.21 and 2.02 the shape is flake and for ratios of 1.5, 1.47, 1.46, 1.16 and 1.1 the particles are sphere form. In spherical nanoparticles, superparamagnetic property with zero coercivity was observed. On the other hand, by increasing the size from about 3 nm to 10 nm, the saturation magnetization reached from 20 emu/gr to 32 emu/gr. For flake particles with higher length to area (2.21 rather than 2.02), this value changed from 7.4 emu/gr to 12.4 emu/gr and coercivity changed from 120 Oe to 625 Oe.