Synthesis, Structural and Magnetic Characterization of Superparamagnetic Ni0.3Zn0.7Cr2−xFexO4 Oxides Obtained by Sol-Gel Method

The sol-gel process was used to produce ferrite Ni0.3Zn0.7Cr2−xFexO4 compounds with x = 0, 0.4, and 1.6, which were then subsequently calcined at several temperatures up to 1448 K for 48 h in an air atmosphere. X-ray diffraction (XRD), scanning electron microscopy (SEM), vibrating sample magnetometer (VSM), and 57Fe Mössbauer spectrometry were used to examine the structure and magnetic characteristics of the produced nanoparticles. A single-phase pure Ni0.3Zn0.7Cr2−xFexO4 nanoparticle had formed. The cubic 𝐹𝑑3m spinel structure contained indexes for all diffraction peaks. The crystallite size is a perfect fit for a value of 165 ± 8 nm. Based on the Rietveld analysis and the VSM measurements, the low magnetization Ms of Ni0.3Zn0.7Cr2−xFexO4 samples was explained by the absence of ferromagnetic Ni2+ ions and the occupancy of Zn2+ ions with no magnetic moments in all tetrahedral locations. Moreover, because of the weak interactions between Fe3+ ions in the octahedral locations, the magnetization of the current nanocrystals is low or nonexistent. According to Mössbauer analyses, the complicated hyperfine structures are consistent with a number of different chemical atomic neighbors, such as Ni2+, Zn2+, Cr3+, and Fe3+ species that have various magnetic moments. A Fe-rich neighbor is known to have the highest values of the hyperfine field at Fe sites, while Ni- and Cr-rich neighbors are responsible for the intermediate values and Zn-rich neighbors are responsible for the quadrupolar component ​
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