Nanorods of iron oxalate synthesized using reverse micelles: facile route for alpha-Fe2O3 and Fe3O4 nanoparticles.

Uniform and smooth nanorods of iron oxalate dihydrate have been synthesized using the reverse micellar route in the presence of the cationic surfactant CTAB (cetyltrimethyl ammonium bromide). These rods have an average diameter of 70 nm and length of 470 nm and show an antiferromagnetic ordering at 27 K. The oxalate rods act as suitable precursor for obtaining a variety of iron oxide nanoparticles depending on the nature of the atmosphere in which decomposition is performed. Spherical alpha-Fe2O3 nanoparticles (approximately 50 nm) were obtained when the nanorods were decomposed in air (500 degrees C) and show a transition from a weakly-ferromagnetic to weakly anti-ferromagnetic behaviour at approximately 225 K which is reminiscent of a Morin-like transition. Cuboidal Fe3O4 nanoparticles (approximately 60-70 nm) were obtained by the decomposition at 500 degrees C in vacuum (approximately 10(-5) torr) and show a Verwey transition at 122 K.