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<p>Cobalt-substituted barium hexaferrite (BaCo₂Fe₁<sub>6</sub>O<sub>27</sub>, x = 0) and its cobalt-nickel co-substituted counterparts (BaCo<sub>1.6</sub>Ni<sub>0.4</sub>Fe₁<sub>6</sub>O<sub>27</sub>, x = 0.4; and BaCo<sub>1.4</sub>Ni<sub>0.6</sub>Fe₁<sub>6</sub>O<sub>27</sub>, x = 0.6) were successfully synthesized via the sol-gel auto-combustion method. This synthesis route allowed for homogeneous mixing and yielded phase-pure hexaferrite structures with controlled morphology. Structural analysis confirmed the formation of the W-type hexaferrite phase, while the incorporation of Co²⁺ and Ni²⁺ ions resulted in notable changes in lattice parameters and crystallite size. The microstructure displays notable grain size heterogeneity, densely packed grains, indicative of partial sintering and strong interparticle interactions. FTIR spectroscopy showed the Fe–O stretching vibrations associated with tetrahedral sites remained largely unaffected by variations in nickel and cobalt substituting concentrations. In contrast, the Fe–O stretching modes at octahedral sites exhibited a slight but discernible redshift, indicating subtle modifications in the local bonding environment. UV-Vis spectroscopy demonstrated a redshift in the absorption edge and a reduction in optical bandgap with increasing Ni content, attributed to modifications in the electronic structure. Magnetic measurements revealed significant enhancement in coercivity and saturation magnetization due to the substitution effects, particularly at higher Ni concentrations. The saturation magnetization (M<sub>s</sub>) initially decreases from 72 emu/g (x = 0.0) to 66.6 emu/g (x = 0.4) due to Fe³⁺ moment dilution by Co/Ni substitution, then recovers to 71.74 emu/g (x = 0.6) as Ni²⁺’s higher moment and improved spin alignment dominate. The magnetic anisotropy constant (K) mirrors this trend declining from 0.361 × 10⁶ erg/cm³ to 0.145 × 10⁶ erg/cm³ before rebounding to 0.339 × 10⁶ erg/cm³ indicating restored anisotropic stability via spin-orbit coupling at higher substitutions. These findings highlight the potential of Co- and Co/Ni-substituted barium hexaferrites for applications in high-frequency devices, microwave absorption, and magneto-optical systems.</p>

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Cation Substitution Effects on Structural, Optical, and Magnetic Evolution in Auto-Combustion Sol-Gel Derived BaCo2 − xNixFe₁6O27 Hexaferrites

  • 期刊论文

  • 发表日期：

    2025年11月26日

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  • Zahraa S. Ahmed,
  • Douaa B. Fahad,
  • Mukhlis M. Ismail

摘要

Cobalt-substituted barium hexaferrite (BaCo₂Fe₁6O27, x = 0) and its cobalt-nickel co-substituted counterparts (BaCo1.6Ni0.4Fe₁6O27, x = 0.4; and BaCo1.4Ni0.6Fe₁6O27, x = 0.6) were successfully synthesized via the sol-gel auto-combustion method. This synthesis route allowed for homogeneous mixing and yielded phase-pure hexaferrite structures with controlled morphology. Structural analysis confirmed the formation of the W-type hexaferrite phase, while the incorporation of Co²⁺ and Ni²⁺ ions resulted in notable changes in lattice parameters and crystallite size. The microstructure displays notable grain size heterogeneity, densely packed grains, indicative of partial sintering and strong interparticle interactions. FTIR spectroscopy showed the Fe–O stretching vibrations associated with tetrahedral sites remained largely unaffected by variations in nickel and cobalt substituting concentrations. In contrast, the Fe–O stretching modes at octahedral sites exhibited a slight but discernible redshift, indicating subtle modifications in the local bonding environment. UV-Vis spectroscopy demonstrated a redshift in the absorption edge and a reduction in optical bandgap with increasing Ni content, attributed to modifications in the electronic structure. Magnetic measurements revealed significant enhancement in coercivity and saturation magnetization due to the substitution effects, particularly at higher Ni concentrations. The saturation magnetization (Ms) initially decreases from 72 emu/g (x = 0.0) to 66.6 emu/g (x = 0.4) due to Fe³⁺ moment dilution by Co/Ni substitution, then recovers to 71.74 emu/g (x = 0.6) as Ni²⁺’s higher moment and improved spin alignment dominate. The magnetic anisotropy constant (K) mirrors this trend declining from 0.361 × 10⁶ erg/cm³ to 0.145 × 10⁶ erg/cm³ before rebounding to 0.339 × 10⁶ erg/cm³ indicating restored anisotropic stability via spin-orbit coupling at higher substitutions. These findings highlight the potential of Co- and Co/Ni-substituted barium hexaferrites for applications in high-frequency devices, microwave absorption, and magneto-optical systems.