Sol–gel synthesis and magnetization study of Mn1−xCuxFe2O4 (x=0, 0.2) nanocrystallites

The magnetic nanoparticles of Mn1−xCuxFe2O4 (x=0, 0.2) were prepared by using a sol–gel method. It is proved that both the MnFe2O4 and Mn0.8Cu0.2Fe2O4 nanoparticle samples have superparamagnetic feature. Although the particle sizes are the same, substitution of a small fraction Cu for Mn results in the increase of magnetocrystallite anisotropy energy, thus enhances the blocking temperature from 130 K for MnFe2O4 to 260 K for Mn0.8Cu0.2Fe2O4. Mössbauer spectroscopy confirms that the anisotropy constant K of the Mn0.8Cu0.2Fe2O4 material is distinctly higher than that of the MnFe2O4 compound. Increase of the blocking temperature suggests that the approach we employed is effective to tackle the ‘superparamagnetic limit’ problem.