Magnetic properties of co-ferrite nanoparticles prepared by co-precipitation method

Co-ferrite nanoparticles were synthesised by coprecipitation method and were annealed at different temperatures in air. Grain size was observed to be increased with the increase in annealing temperature. Magnetisation value of the as-prepared sample was 57 emu/g at 300 K and increased with the increase in annealing temperature. The highest value of 76 emu/g was observed for the sample annealed at 900 degrees C. With the decrease in temperature to 60 K, it was enhanced from that at 300 K and the difference between the magnetisation values observed at 300 and 60 K, decreased with the increase in annealing temperature. The variation of coercivity showed a maximum of 1.02 kOe at 300 K for the nanoparticle sample with grain size of 27 nm. A very high value of energy product (BH)(max) of 5.6 MGOe was observed at 60 K for the sample annealed at 900 degrees C. Both exchange and dipolar interactions were observed in these nanoparticles. The nonsaturation behaviour of magnetic hysteresis loop decreased with the increase in grain size and annealing temperature. The observed magnetic properties can be correlated to grain size, surface defects, anisotropy and interparticle interactions in these nanoparticles.