Zinc ion-substituted cobalt ferrite powders Co_1−xZn_xFe₂O₄ (x = 0–0.7) were prepared by the sol-gel auto-combustion process. The structural properties and magnetic of the samples were investigated with X-ray diffraction (XRD), superconducting quantum interference device, and a Mössbauer spectrometer. The results of XRD showed that the powder of a single cubic phase of ferrites calcined when kept at 800 °C for 3 h. The lattice constant increases with increase in Zn concentration, but average crystallite size does not decrease constantly by increasing the zinc content, which is related to pH value. It was confirmed that the transition from ferrimagnetic to superparamagnetic behaviour depends on increasing zinc concentration by Mössbauer spectra at room temperature. Magnetization at room temperature increases for x ≤ 0.3, but decreases for increasing Zn²⁺ ions. The magnetization of Co_0.7Zn_0.3Fe₂O₄ reached maximum value (83.51 emu/g). The coercivity decreased with Zn²⁺ ions, which were doped on account of the decrease of the anisotropy constant.

Gadolinium substituted cobalt ferrite CoGd_xFe_2−xO₄ (x = 0, 0.04, 0.08) powders have been prepared by a sol‐gel autocombustion method. XRD results indicate the production of a single cubic phase of ferrites. The lattice parameter increases and the average crystallite size decreases with the substitution of Gd³⁺ ions. SEM shows that the ferrite powers are nanoparticles. Room temperature Mössbauer spectra of CoGd_xFe_22−xO₄ are two normal Zeeman‐split sextets, which display ferrimagnetic behavior. The saturation magnetization decreases and the coercivity increases by the Gd³⁺ ions.

Zinc substituted magnesium ferrite nanomaterials Mg_1−xZn_xFe₂O₄ (x = 0, 0.1, 0.3, 0.5, 0.7) powders have been prepared by a sol‐gel autocombustion method. The lattice parameter increases with increase in Zn concentration, but average crystallite size tends to decrease by increasing the zinc content. SEM results indicate the distribution of grains and morphology of the samples. Some particles are agglomerated due to the presence of magnetic interactions among particles. Room temperature Mössbauer spectra of Mg_1−xZn_xFe₂O₄ shows that the A Mössbauer absorption area decreases and the B Mössbauer absorption area increases with zinc concentration increasing. The change of the saturation magnetization can be explained with Néel’s theory. It was confirmed that the transition from ferrimagnetic to superparamagnetic behaviour depends on increase in zinc concentration by Mössbauer spectra at room temperature. Saturation magnetization increases and coercivity decreases with Zn content increasing.

A sol-gel autocombustion method was used to synthesize Al³⁺ ion-substituted cobalt ferrite CoAl_xFe_2−xO₄ (x = 0–1.5). According to X-ray diffraction analysis (XRD), cobalt ferrite was in a single cubic phase after being calcined at 1000 °C for 3 h. Moreover, the lattice constant decreased with increase in aluminum substituents. When the sample was analyzed by Scanning Electron Microscopy (SEM), we found that uniformly sized, well-crystallized grains were distributed in the sample. Furthermore, we confirmed that Al³⁺ ion-substituted cobalt ferrite underwent a transition from ferrimagnetic to superparamagnetic behavior; the superparamagnetic behavior was completely correlated with the increase in Al³⁺ ion concentration at room temperature. All these findings were observed in Mössbauer spectra. For the cobalt ferrite CoAl_xFe_2−xO₄, the coercivity and saturation magnetization decrease with an increase in aluminum content. When the annealing temperature of CoAl_0.1Fe_1.9O₄ was steadily increased, the coercivity and saturation magnetization initially increased and then decreased.