Size effect on the magnetic property of CoAl2O4 nanopowders prepared by reverse micelle processing

Research highlights: → Single phase cobalt aluminate (CoAl2O4) nanopowders can be prepared using the precipitation of hydroxides and their oxidation from the reverse microemulsions of the aqueous solution. → The particle size increases with the increasing water to surfactant ratio. → The specific magnetization, which depends mainly on the particle size, ranged from 0.028 emu g-1 for the particles of approximately 35 nm in size, to 0.23 emu g-1 for the particles of approximately 57 nm in size. - Abstract: Cobalt aluminate (CoAl2O4) nanopowders were synthesized by reverse microemulsion process using cyclohexane, a nonionic surfactant, and aqueous solutions of cobalt (II) nitrate hexahydrate and aluminum nitrate nonahydrate. The influence of water to surfactant molar ratio on the size of powders has been studied. The X-ray diffraction analysis shows that the powders calcined at 1000 oC have single phase cubic spinel structure. The average size of the particles increases with increasing water to surfactant molar ratio. The mean diameter of the particles varies between 42 and 57 nm. The Fourier transform infrared spectra also confirm the formation of CoAl2O4. Magnetization study reveals that the CoAl2O4 sample exhibits superparamagnetic behavior.