A comparative study on the magnetic properties of MFe12O19 and MAlFe11O19 (M = Sr, Ba and Pb) hexaferrites with different morphologies

M-type nano hexaferrites MFe12O19 and MAlFe11O19 (M = Sr, Ba and Pb) have been prepared by the sol–gel method to investigate the shielding effect of inorganic ions KCl, KBr and KI on the phase growth of ferrites. FTIR frequency bands in the range 560–580 cm−1 and 430–470 cm−1corresponds to the formation of tetrahedral and octahedral clusters of metal oxides in ferrites, respectively. X-ray powder diffractographs do not show any peaks for the as obtained samples showing the amorphous nature of the samples, however regular peaks for M-type structure have been obtained for all the annealed samples. There is negligible small change in the lattice parameters ‘a’ and ‘c’ with substitution of the hexagonal ferrites with aluminium. Magnetic measurements showed that the coercivity (Hc) values of all the samples with KCl and KBr enhance due to KCl and KBr to act as deactivators. However, the coercivity value decreases with KI as it oxidise to I2 during annealing. The saturation magnetization of the hexaferrites decreases with Al3+ ion substitution for Fe3+ ion due to preferential occupancy of aluminium in octahedral sites.