Characterization of nanosized spinel ferrite powders synthesized by coprecipitation and autocombustion method

Magnetic nanoparticles of magnetite (Fe3O4) and NiCuZn-doped magnetite (Ni0.35Cu0.15Zn0.5Fe2O4) were prepared by coprecipitation and by sol–gel combustion methods accordingly. The average size, d, of magnetite nanoparticles (d = 12 nm) and the NiCuZn ferrite nanoparticles ignited at about 250 °C (d = 30 nm) was estimated from X-ray diffraction patterns. The Mössbauer spectroscopy revealed the existence of the paramagnetic doublet in both samples. For magnetite, coercive force of about 400 Oe was found at 5 K. Likewise, the coercive field of the NiCuZn-doped magnetite nanoparticles decreases with Fe2+ substitution at low temperature (260 Oe). This behavior can be explained taking into account the fact that the magnetocrystalline anisotropy constant of Fe3O4 is higher than that of NiCuZn ferrite.