Tuning the multiferroic properties of spinel nickel ferrite via zinc doping

This work presents a systematic investigation of the effects of the crystal structure and cation distribution on the multiferroic properties of the zinc-doped ferrite Ni_1-xZn_xFe₂O₄ (0 ≤ x ≤ 1, Δx = 0.1) synthesized via high–energy ball milling followed by heat treatment. X-ray diffraction (XRD) analysis confirmed the successful synthesis of cubic spinel ferrite across all the studied compositions, whereas structural changes, such as lattice size, porosity and crystallite size, exhibited compositional dependence. Scanning electron microscopy (SEM) of the pellet surfaces revealed the dependence of the grain size distribution and porosity on the zinc content. Raman spectroscopy analysis allows the determination of the distribution of cations as a function of the Zn content, revealing the change from an inverse to a mixed spinel structure. X-ray photoelectron spectroscopy (XPS) allows the determination of the cations of Ni²⁺, Ni³⁺, Fe²⁺ and Fe³⁺ distributed in tetrahedral and octahedral sites, resulting in new magnetic and dielectric interactions in the samples. Magnetic hysteresis loops confirmed the ferromagnetic ordering of the synthesized ferrites, with saturation magnetization values ranging from 40 to 76 emu/g for 0 to 0.5 mol of Zn, respectively. The observed increases in relative permittivity and conductivity with increasing zinc content are attributed to the redistribution of Fe³⁺ ions within the crystal lattice, which is modulated by the Zn doping level. These findings confirm that bulk zinc-doped nickel ferrites synthesized by high–energy ball milling exhibit improved ferromagnetic and dielectric properties, suggesting potential for expanded technological applications.