Study of structural, dielectric, and magnetic properties of nickel doped strontium hexaferrite nanoparticles for microwave absorption application

Abstract This study presents the fabrication of nickel-doped strontium hexaferrite nanoparticles via the sol–gel auto-combustion technique to evaluate their potential as efficient microwave absorbing materials. A compositional series of Sr 1−x Ni x Fe 12 O 19 (x = 0.00, 0.20, 0.35, and 0.50) was synthesized to investigate the influence of Ni substitution on structural, magnetic, dielectric, and microwave absorption properties. XRD analysis confirmed the successful formation of a single-phase M-type hexaferrite structure with slight lattice distortion due to Ni incorporation, while crystallite sizes were estimated to range between 29 and 39 nm. FTIR spectra revealed characteristic metal–oxygen vibrational modes in tetrahedral and octahedral coordination, affirming phase purity at the atomic scale. Magnetic characterization using a vibrating sample magnetometer (VSM) demonstrated an increase in saturation magnetization (Ms) from 37.26 to 44.12 emu g −1 , accompanied by a significant reduction in coercivity from 5000 Oe to 3800 Oe as Ni content increased to x = 0.50, indicating a softening of magnetic behavior favorable for microwave applications. Dielectric and magnetic loss mechanisms were further analyzed through complex permittivity and permeability measurements, where ε ′ increased from 2.4 to 5.6 and μ ′ from 2.0 to 1.5 across the series, reflecting enhanced interfacial polarization and magnetic resonance effects. Notably, the sample with x = 0.50 exhibited the best combination of dielectric and magnetic parameters ( ε ′ = 5.6, ε ″ = 0.45, μ ′ = 1.5, μ ″ = 1.3 at 1 GHz), contributing to effective electromagnetic attenuation. Microwave absorption measurements in the X-band (8–12 GHz) revealed that all samples exhibited substantial reflection loss, with the x = 0.50 composition achieving a maximum RL of –22.50 dB at 9.26 GHz and a normalized input impedance (Zin/Zo) of approximately 0.8, signifying excellent impedance matching. These comprehensive findings strongly support the potential of Ni-doped Sr hexaferrite nanoparticles as high-performance, tunable, and lightweight microwave absorbing materials suitable for EMI shielding and stealth applications.