Effect of calcium solubility on structural, microstructural and magnetic properties of M-type barium hexaferrite

Abstract

We report the synthesis of x = 0.00–1.00 at step size of 0.10 for Ba1-xCaxFe12O19 samples using sol-gel auto combustion method. The powder X-ray diffraction (XRD) data of 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 at. % (x = 0.50) at 1200 °C; c) a decrease in lattice parameters ‘c’ (from 23.2002 Å (x = 0.00) to 23.0928 Å (x = 0.50)) as well as cell volume (from 696.75 Å3 (x = 0.00) to 692.95 Å3 (x = 0.50)) with increasing ‘x’ and d) the presence of segregated (α–Fe2O3) phase for x ≥ 0.20 at 900 °C and for x > 0.50 at 1200 °C. As the maximum calcium solubility in BaM phase has been noticed at 1200 °C, most of the other characterizations have been performed on these samples only. FESEM micrographs show an increase in particle size with ‘x’. Magnetic measurements reveal that the highest value of saturation magnetization (Ms) is ≈71.82 emu/g (calcined at 1200 °C) in x = 0.50 sample. The coercivity (Hc) decreases from 3765Oe to 1729Oe with increase in ‘x’. Among the samples calcined at different temperatures, the coercivity (Hc) decreases from 4726Oe to 2040Oe with an increase in calcination temperature for x = 0.20 samples. The samples because of their excellent magnetic properties could be vital for magnetic recording and for applications as permanent magnets.