Synthesis of polycrystalline CoFe₂O₄ and NiFe₂O₄ powders by auto-combustion method using a novel amino-based gel

Polycrystalline CoFe₂O₄/NiFe₂O₄ powders were prepared by auto-combustion method using a novel amino-based gel. The thermal evolution of gel precursors, as well as the microstructure, morphology and magnetic properties of as-synthesized powders were studied in detail. Energy dispersive x-ray spectroscopy indicated that the ratios of Ni:Fe was close to the theoretical value (Ni:Fe  =  1:2), suggesting high purity of synthesized NiFe₂O₄ powders. The saturated magnetization (M _s) and residual magnetization (M _r) of CoFe₂O₄ were highly dependent upon the annealed temperatures. The M _s increased from 77.5 to 84.7 emu g⁻¹, and M _r increased from 37.7 emu g⁻¹ to 42.5 emu g⁻¹ by annealing from room temperature to 600 °C. The M _s of NiFe₂O₄ was 38.7 emu g⁻¹, much lower than that of CoFe₂O₄. The experimental results indicated that this auto-combustion method using amino-based gel was a suitable method for synthesizing high-quality CoFe₂O₄/NiFe₂O₄ powders. (paper)