Synthesis and magnetic microstructure of nanoparticles of zinc-substituted magnesium ferrites

Nano-sized magnesium-zinc powders are synthesized, by using the sol-gel autocombustion technology. On the basis of Xray researches, the phase composition of non-magnetic substituted ferrite systems is determined. The resulting complex oxide powders are found to be agglomerated. The agglomerates consist of several nanoparticles with an average size of 18-32 nm. According to the cation distribution in magnesium zinc ferrites, Zn²⁺ cations are found to occupy positions in the tetrahedral sublattice (A-sites) and displace Fe³⁺ cations into the octahedral sublattice (B-sites). The Moessbauer spectrum registered for the magnesium ferrite powder at room temperature shows two characteristic Zeeman sextets. For ferrites substituted with non-magnetic cations, the Moessbauer spectra are superpositions of several sextets and superposing doublets.The studies also show that the shape of Zeeman spectral lines depends on the particle size, which testifies to their superparamagnetic properties. The dependence of Moessbauer parameters such as the isomer shift, the quadrupole splitting, and the hyperfine magnetic field on the Zn²⁺ ion concentration is discussed. It is supposed that a change of the effective magnetic with increasing the zinc content in magnesium zinc ferrites is related to the fact that the substitution of Fe³⁺ cations by Zn²⁺ ones reduces the indirect exchange interaction between the A and B sublattices in ferrites with the spinel structure, which actually leads to their magnetic ordering