Effect of calcium solubility on structural, microstructure and magnetic properties of SrFe12O19

The synthesis of Sr_1-xCa_xFe₁₂O₁₉ (x = 0.0–1.0 at increments of 0.1) samples is reported via a sol-gel auto-combustion process. XRD data for Sr_1-xCa_xFe₁₂O₁₉ samples calcined at different temperatures indicates a) single-phase formation up to x = 0.20 in samples calcined at 900 °C, b) an increase in calcium solubility to 50 atomic % (x = 0.50) at 1200 °C, c) a decrease in lattice parameters and cell volume with increasing 'x' and d) the presence of segregated α–Fe₂O₃ phase for x > 0.50 at 1200 °C and for x ≥ 0.20 at 900 °C. As the maximum Ca solubility in SrM (SrFe₁₂O₁₉) phase has been observed at 1200 °C, most of the other characterizations have been performed on these samples only. An increase in grain size with 'x' was revealed in FESEM micrographs. Magnetic measurements show that in the x = 0.50 sample the maximum saturation magnetization (M_s) value is ≈ 70.67 emu/g. Coercivity (H_c) decreases monotonically, with an increase in Ca content in SrM (SrFe₁₂O₁₉), from 3822 Oe (x = 0.00) to 2045 Oe (x = 0.50). Among the samples calcined at different temperatures, coercivity (H_c) decreases monotonically from 5650 Oe to 3128 Oe with an increased calcination temperature for samples of x = 0.20. The samples could be vital for magnetic recording and applications as permanent magnets due to their excellent magnetic properties.