S. S. Madani - Islamic Azad University, North Tehran Branch, Tehran, Iran
G. Mahmoudzadeh - Islamic Azad University, North Tehran Branch, Tehran, Iran
S. Abedini Khorrami - Islamic Azad University, North Tehran Branch, Tehran, Iran

Magnetic ceramic materials, spinels of the type A2+B3+2O4 such as; ZnFe2O4 and CoFe2O4 have attracted considerable attention due to their wide applications in several technological fields [1]. As we know, a lot of factors affect the characteristics of ferrites, such as the synthesis method, the ratio of Fe to Zn or Co, as well as the molar ratio of urea to the metal nitrate, pH in the starting solution, the annealed temperature and other parameters [2]. In the present study, a solution of metal nitrates and urea has been used to prepare zinc ferrite and cobalt ferrite. The detailed process can be described as follows: Zinc nitrate tetra hydrate (Zn(NO3)2∙4H2O, Merck), cobalt nitrate hexa hydrate (Co(NO3)2.6H2O, Merck), iron nitrate nona hydrate (Fe(NO3)3∙9H2O, Merck), urea (CO(NH2)2, Merck) and NH4OH (Merck) was obtained with analytical grade. All materials were used without further purification. The molar ratios of metal nitrates to urea were taken as 1:1.2. The metal nitrates were dissolved together in a minimum amount of double distilled water to get clear solutions. Aqueous solutions of urea were mixed with metal nitrates solutions, then ammonia solution was slowly added to adjust the pH about 8. The mixed solutions were kept on to a hot plate with continuous stirring at 90C. During evaporation, the solutions became viscous and finally formed very viscous brown gels. After few minutes, the gels automatically ignited in 350°C and burnt with glowing flints. The auto-ignition was completed within a minute, yielding the brown-colored ashes termed as a precursor. The as-prepared powders of all the samples were heat treated separately at 750C for 4 h to get the final products. These powders were characterized by X-ray diffraction and scanning electron Microscopy. XRD results showed that ZnFe2O4 and CoFe2O4 powders have cubic spinel structures. Particle size and morphology of nanocrystalline was determined by XRD and SEM, respectively.