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 11nm from XRD and 11.4nm from TEM: magnetic domain size is 9.7nm. The saturation magnetization is 390emu/cm 3 at 300K, and T B is 134K. The reduction of magnetic particle size and M s 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, T B , is attributed to a large degree of inversion of the Fe 3 O 4 particles. Results also indicated the existence of interparticle interactions in the thermomagnetic characteristics of spinels at lower field strengths.