Synthesis, structural and magnetic characterization of ZnxFe3-yO4 nanocrystalline particles prepared by precipitation under reflux method
Author
Al-Hamouda, Abdulmohsen Salem Abdullah.
English abstract
Nanocrystalline ZnxFez-yO4 (y = 2x/3) samples were prepared using the precipitation under reflux method and investigated both structurally and magnetically. TEM reveals the particles to have almost spherical shape with radii ranging between 10 to 40 nm. Rietveld refinement of the XRD data and Mössbauer spectroscopy have shown the sample with x = 0.00 to be composed of magnetite and maghemite in the ratio of ~4:1 respectively. Doping with Zn2+ ions was found to inhibit the magnetite-to-maghemite transformation. This was related to the possible presence of the dopant Zn2+ ions entirely on the shells of the nanoparticles to prevent the oxidization of the Fe2+ ions at the interior core of the magnetite nanoparticles. XRD and Mössbauer spectroscopy have consistentlyshown that the Zn2+ ions exclusively occupy the tetrahedral A-sites in the spinel-related structure.
The Mössbauer quadrupole shifts indicate that the cubic symmetry remains
almost unchanged at the 57Fe nuclear site upon Zn2+ doping. The Mössbauer hyperfine
magnetic fields at both spinel crystallographic sites decrease with increasing x suggesting
weaker magnetic super-exchange interactions as the more of the diamagnetic Zn2+ ions
are incorporated in the material. More ZnyFe3-y04 particles tend to be superparamagnetic
as x value increases, with blocking temperature > 80 K. In consistency with Néel's model
of ferrimagnetism, the substitution of Zn2+ at the tetrahedral sites was found to increase
the saturation magnetization with increasing x up to x = 0.30 where a value similar to that
of bulk magnetite was attained. The decrease in the saturation magnetization for the
samples with x = 0.40 and 0.50, was explained in terms of spin canting. The coercivity
decreased with increasing the Zn2+ content in in the ZnxFez-yO4 samples.
