Ca²⁺/Mg²⁺ co-substituted strontium nanohexaferrites: magnetic investigation and Mossbauer analysis

We report a comprehensive evaluation of the microstructures, magnetic, and hyperfine traits of Ca²⁺/Mg²⁺ co-substituted strontium nanohexaferrites (SHFs) of chemical compositions Sr_1–2xCa_xMg_xFe₁₂O₁₉ (x ≤ 0.1). These SHFs were prepared using sol–gel unified auto-combustion strategy and characterized by diverse analytical measurements to determine the effects of Ca²⁺/Mg²⁺ co-substitution on the aforesaid properties. XRD and high resolution transmission electron microscpe (HRTEM) analyses confirmed the nucleation of HF nanocrystallites. UV-visible diffuse reflectance (DR–UV–Vis) spectra were used to evaluate the optical band gap of the proposed SHFs, which was reduced with the increase in co-substitution contents. The ⁵⁷Fe Mössbauer spectra was exploited to assess the quadrupole splitting, spectral line-width variation, isomer shift, distribution of cations (Ca²⁺ and Mg²⁺), and hyperfine magnetic fields. Measured magnetic parameters such as saturation magnetization, remanence, squareness ratio (SQR), coercivity, and magnetic moment were significantly improved due to the Ca²⁺/Mg²⁺ co-substitution. All the prepared SHFs revealed ferrimagnetic nature both at 10 and 300 K. Achieved SQR values ≈0.5 of the studied SHFs clearly disclosed their single domain character possessing uniaxial anisotropy.