Abstract: A method for forming monodispersed magnetic nanoparticles of manganese zinc ferrite is provided which includes reversed micelle synthesis. The method includes preparing a micelle solution of zinc, manganese and iron salts, a surfactant and a hydrocarbon and mixing a second micelle solution of ammonium hydroxide, a surfactant and a hydrocarbon with the first solution to precipitate a ferrite precursor precipitate. The ferrite precursor precipitate is recovered, washed and annealed to produce nanoparticles of manganese zinc ferrite having a spinel crystal structure. Advantageously, the resulting nanoparticles of manganese zinc ferrite have a length no greater than 50 nm in any of the three spatial dimensions and the particle size distribution has a standard deviation of greater than 12% of the mean value.