Abstract
Background: Among different metal oxides, ferrites play an important role in many fields such as transformers, gas sensors and energy storage and conversion. The magnetic properties of Co-ferrites are due to the cation distribution among octahedral and tetrahedral sites. Such distribution can be controlled by the preparation method which in its turn depends on the particle size and morphology. Among different synthesis techniques, microwave induced combustion method is rapid and convenient.
Methods: Co-Ferrite nanoparticles have been synthesized through a reaction of a mixture of stoichiometric of Co-nitrate hexahydrate, Fe-nitrate nonahydrate, and urea. Different urea to metal nitrates ratio have been used. The mixture is dissolved in an appropriate amount of doubly distilled water then transferred to a commercial microwave oven operating at 800 W for 20 minutes.
Results: Sample synthesized at low urea/metal nitrate ratio (1:1) shows undesirable mixed phases namely Co3O4, Fe2O3 together with CoFe2O4. With increasing urea ratio, the detected diffraction peaks are well indexed to CoFe2O4 phase and all other secondary phases are disappeared. It was found that the crystallite size increases with increasing the urea/metal nitrates ratio. The high resolution transmission electron microscope provides a further confirmation for the formation pure Co-ferrite phase. Additionally the magnetic properties such as saturation magnetization and coercivity are measured and found to depend on the urea/metal nitrates ratio.
Conclusion: In this study, CoFe2O4 nanoparticles have been successfully fabricated by microwave assisted combustion method. The effect of urea/metal nitrates ratio on the structure and magnetic properties is studied. The XRD results showed that a single CoFe2O4 phase can be obtained at urea/metal nitrates ratio >= 2. The crystallite size was estimated to be in the range 10.33-23.29 nm. The studied system shows a high saturation magnetization of about 65 emu/g for the 13.13 nm sized particles. The critical size was found to be about 13 nm with the highest coercivity of about 1200 Oe.