A method for making monodispersed magnetic nanoparticles of nickel zinc ferrite (NZFO) at room temperature by mixing together two micelle solutions. The first micelle solution comprises zinc, nickel, and iron metal salts; a surfactant; and a hydrocarbon. The second micelle solution comprises an aqueous hydroxide, a surfactant, and a hydrocarbon. After mixing the two micelle solutions, the ferrite precipitates.