Mohammed Ahmed Wahba
M-type BaFe12O19 is a technologically important ferrite owing to its large uniaxial anisotropy, chemical robustness, and relevance to magnetic and high-frequency devices. Here, pristine BaFe12O19 (BF), Ba0.97Ce0.03Fe11.97Ni0.03O19 (CNBF), and Ba0.97Nd0.03Fe11.97Ni0.03O19 (NNBF) nanocompositions were synthesized by a sol-gel route to probe the effect of Ni/rare-earth co-substitution on the coupled structural, optical, dielectric, and magnetic responses. Rietveld-refined X-ray diffraction data confirmed retention of the magnetoplumbite structure in all samples, with a slight lattice contraction upon co-substitution, most evident for NNBF. Microstructural analysis revealed a denser and more homogeneous morphology for CNBF, whereas NNBF showed greater heterogeneity, consistent with stronger local structural perturbation. Optical measurements showed that the band gap changed from 1.647 eV for BF to 1.652 eV for CNBF, while a lower value of 1.631 eV was obtained for NNBF; similarly, the Urbach energy results suggested lower disorder in CNBF and more pronounced localized states in NNBF. A pronounced suppression of the low-frequency dielectric constant was observed, decreasing from ∼2750 in BF to ∼1230 in CNBF and ∼1080 in NNBF, accompanied by lower dielectric loss, indicative of reduced interfacial polarization and improved charge compensation. Magnetically, co-substitution markedly enhanced the saturation magnetization from 28.04 emu g-1 (BF) to 36.75 emu g-1 (CNBF) and 36.41 emu g-1 (NNBF), while reducing the coercive field from 3361 Oe to 3008 and 2804 Oe, respectively. The maximum energy product also increased to 2.81 × 105 erg g-1 for CNBF. These results show that Ni/rare-earth co-substitution is a suitable route to adjust the multifunctional performance of BaFe12O19 with the Ce/Ni co-doping providing the best overall response among the studied compositions.