Magnetic nanocrystalline materials cover a broad spectrum of industrial applications. Here we present the optimization of the traditional reverse micelle process, which is a surfactant-stabilized water-in-oil microemulsion synthesis technique, to produce different phases of magnetic iron oxide in bulk. The size of the nanoparticles produced was carefully tuned and greatly depended upon the synthesis conditions such as pH, temperature, concentration of reactants, and the water-to-surfactant ratio. The thermal stability of the synthesized iron oxide particles was investigated using the x-ray...