Magnetic Properties of Mg x Mn1−x Fe2O4 Nanoferrites

We report the magnetic properties of Mg x Mn1−x Fe2O4 (0≤x≤1.0) nanosize compounds with particle sizes between 8 nm and 15 nm. The evolutions of the properties as a function of composition have been investigated by X-ray diffraction, Mössbauer, and SQUID magnetometry. Pure cubic spinel could be obtained under a low reaction temperature of 200°C in all the samples. Impurity phases have been observed in compounds annealed at above 900°C. Magnetic relaxation is observed in samples with particles of about 8 nm. The spectra with particle sizes larger than 10 nm could be fitted with at least two sextets attributed to Fe3+ ions on tetrahedral (A) and octahedral (B) sites. The magnetization measurement indicates superparamagnetic behavior in nanosized compounds.