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<p>Nanocrystalline Co–Al co-substituted strontium hexaferrites, Sr<sub>1-x</sub>Co<sub>x</sub>Fe<sub>12-2x</sub>Al<sub>x</sub>O<sub>19</sub> (x= 0.0–0.4), were successfully synthesized via a sol–gel auto-combustion method and systematically investigated for their structural, microstructural, magnetic, dielectric, and microwave absorption characteristics. X-ray diffraction confirmed the retention of the single-phase M-type hexaferrite structure with progressive lattice contraction upon substitution, while FESEM/TEM analyses revealed nanoscale hexagonal grains with refined morphology and clean grain boundaries. Magnetic measurements showed hard magnetic behavior with high coercivity (6065 Oe for x = 0.0) and moderate saturation magnetization, both decreasing systematically due to magnetic dilution and anisotropy reduction from Al<sup>3+</sup> incorporation. Dielectric studies exhibited enhanced permittivity and strong relaxation-type polarization, while AC conductivity followed Jonscher’s universal power law with a substantial rise in conductivity for substituted compositions. Complex permittivity/permeability analysis revealed that Co–Al substitution tunes impedance matching and intrinsic loss mechanisms; the optimized composition x = 0.3 achieved a minimum reflection loss (RLof –38.5&#xa0;dB and an effective absorption bandwidth (EAB) of 4.2&#xa0;GHz in the X-band (8–12&#xa0;GHz). The improved attenuation arises from synergistic magnetic and dielectric loss, enhanced interfacial polarization, and an increased attenuation constant (α). These results establish Co–Al co-substituted SrFe<sub>12</sub>O<sub>19</sub> as an efficient, rare-earth-free, broadband microwave absorber suitable for EMI shielding and stealth applications.</p>

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Synergistic effect of Co–Al substitution and magnetic–dielectric tuning on microwave absorption in SrFe12O19 hexaferrites nanoparticles

  • 期刊论文

  • 发表日期：

    2025年11月11日

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  • Rashmi A. Thite,
  • Pallavi S. Salunke,
  • Manisha R. Patil,
  • K. M. Batoo,
  • M. Hadi,
  • Akash V. Fulari,
  • C. S. Munnolli,
  • Y. S. Madansure,
  • Maheshkumar L. Mane,
  • Sagar E. Shirsath,
  • R. H. Kadam

摘要

Nanocrystalline Co–Al co-substituted strontium hexaferrites, Sr1-xCoxFe12-2xAlxO19 (x= 0.0–0.4), were successfully synthesized via a sol–gel auto-combustion method and systematically investigated for their structural, microstructural, magnetic, dielectric, and microwave absorption characteristics. X-ray diffraction confirmed the retention of the single-phase M-type hexaferrite structure with progressive lattice contraction upon substitution, while FESEM/TEM analyses revealed nanoscale hexagonal grains with refined morphology and clean grain boundaries. Magnetic measurements showed hard magnetic behavior with high coercivity (6065 Oe for x = 0.0) and moderate saturation magnetization, both decreasing systematically due to magnetic dilution and anisotropy reduction from Al3+ incorporation. Dielectric studies exhibited enhanced permittivity and strong relaxation-type polarization, while AC conductivity followed Jonscher’s universal power law with a substantial rise in conductivity for substituted compositions. Complex permittivity/permeability analysis revealed that Co–Al substitution tunes impedance matching and intrinsic loss mechanisms; the optimized composition x = 0.3 achieved a minimum reflection loss (RLof –38.5 dB and an effective absorption bandwidth (EAB) of 4.2 GHz in the X-band (8–12 GHz). The improved attenuation arises from synergistic magnetic and dielectric loss, enhanced interfacial polarization, and an increased attenuation constant (α). These results establish Co–Al co-substituted SrFe12O19 as an efficient, rare-earth-free, broadband microwave absorber suitable for EMI shielding and stealth applications.