Magnetic properties of Zn-ferrite nanoparticles prepared by sol-gel and coprecipitation methods

Zn-ferrite nanoparticles were synthesized by sol-gel and coprecipitation methods and were annealed at different temperatures in air for 2 h. Grain size of the as-prepared samples was 6 and 13 nm for the samples prepared by coprecipitation and sol-gel methods respectively. It was increased with the increase in annealing temperature in both the cases. The as-prepared sample prepared by coprecipitation method showed superparamagnetic behavior whereas the sample prepared by sol-gel method showed ferrimagnetic behavior. The magnetization values of 5 and 11 emu g⁻¹ were observed at 300 K for the as-prepared samples synthesized by coprecipitation and sol-gel methods respectively. The magnetization and coercivity decreased with the increase in annealing temperature. The magnetization values were enhanced at 60 K compared to those at 300 K. The highest magnetization of 37 emu g⁻¹ was observed at 60 K for the sample annealed at 350 °C prepared by coprecipitation method. In the temperature dependent magnetization curves, the blocking temperature (T_B), Neel temperature (T_N) and irreversible temperature (T_irr) decreased with the increase in the applied fields. The observed magnetic properties can be understood on the basis of grain size and their distribution, and cation distribution in these nanomaterials with the increase in annealing temperature. (paper)