Preparation and study of lattice structure and magnetic properties of Bi³⁺ ion-doped Ni–Mg–Co ferrites by sol–gel auto-combustion method

In this paper, Bi³⁺ ion-doped Ni–Mg–Co ferrite nanomagnetic materials were prepared by sol–gel auto-combustion method using high-purity nitrates and citric acid experimental materials. The effect of Bi³⁺ ion content on the lattice structure and magnetic properties of nanoferrite was also studied. XRD diffractogram analysis shows that the Ni–Mg–Co ferrite samples with x = 0 and 0.025 have single-phase cubic spinel structure. It is found that when the doping amount is 0.05 or >0.05, the secondary-phase Bi₂O₃ peak appears. The average crystallite size of the sample was calculated by Debye–Scheller formula. It was found that the average grain size of the sample was affected by the doping concentration. With the increase in Bi³⁺ ion content, the average crystallite size increases from 8.3797 nm to 8.3940 nm. The structure of Bi³⁺ ion-doped Ni–Mg–Co ferrite was further characterized by FT-IR. There are two absorption bands ν₁ and ν₂ at 584 and 397 cm⁻¹, which further prove the spinel structure. The morphology of the sample particles was observed by SEM, and the distribution of the particle size was calculated. The chemical components of powder samples were analyzed by EDS. Through VSM analysis, the Bi³⁺ ion-doped Ni–Mg–Co ferrite has the characteristics of ferromagnetism. With the increase in Bi³⁺ ion content, the residual and saturation magnetization decreased; the magnetic stability is also reduced. The results show that the magnetic properties of Bi³⁺ion-doped Ni–Mg–Co ferrite are decreased.