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 degrees 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/cm(3) at 300 K, and TB is 134 K. The reduction of magnetic particle size and M-s is attributed to the presence of non-magnetic (dead) surface layer, compositional variations, superparamagnet 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 Fe3O4 particles. Results also indicated the existence of interparticle interactions in the thermomagnetic characteristics of spinels at lower field strengths.