Because of their scientific and technological utility, magnetic properties of fine-particle systems have assumed great importance in recent years. Maghemite (gamma-Fe2O3) and magnetite (Fe3O4) are commonly used in magnetic inks, as catalysts, and as ferrofluids for biomedical uses. In the current work, we report a novel one-step process for the synthesis of different iron oxide phases, including maghemite and magnetite, using the aqueous combustion synthesis technique. The method involves a self-sustained reaction between an oxidizer (e.g., metal nitrate) and a fuel (e.g., glycine or hydrazine). Using this approach, for the first time, spherical, nanoscale (6-10 nm) iron oxide particles with excellent ferrimagnetic properties were synthesized. While the samples have particle sizes of < 10 nm, they exhibit ferrimagnetic behavior at room temperature, as opposed to super-paramagnetism, as reported previously by numerous workers. Further, particularly for Fe3O4, the coercivity values are exceptionally high (213 Oe), indicating stable magnetization.