Structural and magnetic studies of (Mg, Sr)0.2Mn0.1Co0.7Fe2O4 nanoferrites

The (Mg, Sr)0.2Mn0.1Co0.7Fe2O4 nanoferrites were synthesized at low reaction temperature of 200 °C using the glycol–thermal method. Single-phase cubic spinel structure and nanoparticle structure of the synthesized samples were confirmed by X-ray diffraction and high-resolution transmission electron microscope. The results show that the produced powders of the as-prepared samples have average crystallite size of about 8 nm. The evolutions of the magnetic properties as a function of composition, annealing temperature (300–1000 °C) under argon atmosphere or measuring temperature (4–300 K) were investigated by 57Fe Mössbauer spectroscopy, vibration sample magnetometer and superconducting quantum interference device. The Mössbauer spectra indicate ferrimagnetic behavior of the compounds. Significant increase in coercive field with the reduction in measuring temperature is obtained for Sr0.2Mn0.1Co0.7Fe2O4 and Mg0.2Mn0.1Co0.7Fe2O4 which have large coercive fields of 3.02 and 10.70 kOe at 4 K respectively compared to about 0.05 kOe at room temperature. The coercive fields and saturation magnetizations appear to vary with measuring temperature according to Kneller’s law and modified Bloch’s law respectively.

► (Mg, Sr)0.2Mn0.1Co0.7Fe2O4 nanoferrites were produced by glycol–thermal method.
► Coercive fields and hyperfine fields are enhanced by thermal annealing.
► Samples become magnetically harder at lower temperature due to spin freezing.
► Temperature dependence of coercive fields follows Kneller’s law.
► A modified Bloch’s law fits the temperature dependent saturation magnetizations.