Structural, Degree of Inversion, and Magneton Number Studies on Fe3+‐Substituted MAl2O4 (M = Ni, Cu, Zn) Spinel Powders: The Evidence for Local Site Exchange of Cation and Magnetization Increment

Abstract

Nanocrystalline Fe‐substituted metal aluminates, MFe x Al2−x O4 powders (M = Ni2+, Cu2+, and Zn2+) with different Fe3+ ion concentrations (x = 0, 0.5, 1.0, 1.5, and 2), are successfully synthesized by the sol–gel auto combustion method. Characterization of the calcined samples is carried out using X‐ray diffraction (XRD), synchrotron Extended X‐ray Absorption Fine Structure (EXAFS), and vibrating sample magnetometer (VSM) measurements. The XRD results confirm the formation of single‐phase spinel structure with Fd‐3m space group of all samples. The EXAFS spectra illustrate the main translocation trends in the trivalent and divalent ions between the tetrahedral and octahedral sublattices. When XRD Rietveld refinement, Williamson–Hall analysis, and EXAFS curve‐fitting analysis are applied to the data, the precise structural parameters, degree of inversion, and cation site occupancy are obtained. Furthermore, the Fe‐substituted samples show intense increase in the saturation magnetization with the increasing of Fe3+ ion concentrations. This occurrence is due to the rise in the net magnetic moment of the modified aluminates which took place as the distribution of the cations within the structure underwent changes. It is possible to explain the variation observed in the magneton number in the context of Fe3+ content through the application of Néel's collinear spin ordering model.