Structural transformation and magnetic properties of copper ferrite nanoparticles prepared by sol–gel method

Copper ferrite nanoparticles were synthesized by sol–gel method by varying metal nitrate to citric acid (M:C) ratio as 1:1, 1:2, 1:3 and 2:1 and were subsequently annealed at different temperatures ranging from 400 to 900 °C in air for 3 h. These nanoparticle samples were characterized by X-ray diffraction, Fourier transformed infrared spectroscopy, Raman spectroscopy, field emission gun scanning electron microscopy and vibrating sample magnetometer. X-ray diffraction studies showed the as-prepared nanoparticles prepared with M:C ratio 1:1, 1:2, and 2:1 are mostly cubic Cu-ferrite. After annealing phase transformation occurred from cubic to tetragonal Cu-ferrite with increase in c/a ratio. Magnetization value decreased and coercivity increased with the increase in annealing temperature and c/a ratio for the samples prepared with M:C = 1:1 and 1:2. For the samples prepared with M:C = 1:3, the magnetization increased with the increase in annealing temperature whereas for the samples prepared with M:C = 2:1, a minimum was observed in the magnetization values for the sample annealed at 600 °C. The highest magnetization values of 45.6 and 49.5 emu/g at 300 and 60 K, respectively were observed in the present study for the as prepared sample prepared with M:C = 2:1. The highest coercivity of 1530 and 1690 Oe at 300 and 60 K, respectively were observed for the sample prepared with M:C = 1:3 and annealed at 800 °C. The observed magnetic properties can be understood on the basis of phase transformation, increase in tetragonal distortion and c/a ratio, and grain growth in these nanoparticles.