Cation distribution and related properties of MnxZn1−xFe2O4 spinel nanoparticles

• MnxZn1−xFe2O4 (x = 0.05…0.9) nanoparticles were prepared via sol–gel process.
• Structural and magnetic properties are studied by various experimental techniques.
• Inversion degree is estimated on the basis of the cubic lattice parameter.
• XANES measurements are used to monitor the oxidation state of Mn.
• We discuss interdependencies of magnetic properties, stoichiometry and inversion.

MnxZn1−xFe2O4 (x = 0.05…0.9) nanoparticles prepared via sol–gel hydrothermal process were investigated by X-ray powder diffractometry (XRPD), transmission electron microscopy (TEM), 57Fe Mössbauer spectroscopy (MS), electron paramagnetic resonance spectroscopy (EPR), X-ray absorption near edge structure spectroscopy (XANES) and magnetic hysteresis measurements. XRPD measurements revealed a non-monotonic dependence of the cubic lattice parameter on the Mn concentration, which is interpreted as being the result of a corresponding variation in the inversion degree (concentration of Fe ions on the occupied tetrahedral lattice sites) of the studied spinels. XANES measurements indicated that the average oxidation state of Mn ions decreases with the applied Mn concentration, in contrast with Fe ions that were found to be exclusively in the 3+ oxidation state by MS measurements. EPR spectra recorded as a function of temperature enabled the determination of the characteristic anisotropy energy barrier of the superparamagnetic particles, and contributed to the clarification of peculiarities of the corresponding 57Fe Mössbauer spectra. On the basis of the observed results the interdependences among the sample stoichiometry, the cubic cell parameter, the particle size, the inversion degree, the magnetic ordering temperature and the effective magnetic anisotropy are discussed.

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