Synthesis of nickel ferrite nanoparticles by sol-gel method

Abstract NiFe 2 O 4 nanoparticles were prepared by the sol-gel method using polyacrylic acid (PAA) as a chelating agent. It was shown that pure spinel NiFe 2 O 4 nanoparticles with a diameter of 5∼30 nm and a specific surface area of 20.0∼55.2 m 2 /g could be produced by calcining the gel precursors with various molar ratios of PAA to total metal ions (0.5∼2.0) in air at 300°C for 2h. As the molar ratio of PAA to total metal ions increased, particle sizes decreased but the crystallinity increased, revealing PAA not only worked as a chelating agent to disperse the cations homogeneously but also contributed its combustion heat to increase the crystallinity of NiFe 2 O 4 nanoparticles. Moreover, the magnetic analysis showed the resultant NiFe 2 O 4 nanoparticles might be superparamagnetic. Their saturation magnetization (0.19 emu/mol at 298 K) was slightly lower than that for bulk materials due to small size and increased slightly with decreasing the temperature below 360 K