Synthesis of Fe3O4 nanoparticles at 100 °C and its magnetic characterization

Superparamagnetic iron oxide nanoparticles were synthesized by a novel, simple and cost-effective gel-to-crystalline method by alkalizing ferrous chloride with ammonium hydroxide at 80–100 °C under refluxing conditions. Average crystallite size is determined as 11 nm from XRD and 11.4 nm from TEM: magnetic domain size is 9.7 nm. The saturation magnetization is 390 emu/cm3 at 300 K, and TB is 134 K. The reduction of magnetic particle size and Ms is attributed to the presence of non-magnetic (dead) surface layer, compositional variations, superparamagnetic relaxation and spin canting because of the ultrafine nature of the material. The maximization in magnetization near the blocking temperature, TB, is attributed to a large degree of inversion of the Fe3O4 particles. Results also indicated the existence of interparticle interactions in the thermomagnetic characteristics of spinels at lower field strengths.