Cations distribution and magnetic properties of Co–Zr doped BaCoxZrxFe(12−2x)O19 prepared via citrate precursor sol–gel route

The aim of this work is to investigate the correlation between the distribution of cations over five crystallographic positions and magnetic properties of Ba-hexaferrites (BHF) in the coupled substitution of magnetic Co2+ and non-magnetic Zr4+ for Fe3+. We have accomplished the synthesis of Co–Zr doped BaCoxZrxFe(12−2x)O19 (x=0.0, 0.2, 0.4, 0.6, 0.8 and 1.0) by citrate precursor sol–gel method under acidic conditions. These compounds were characterized by TGA–DTA, FT-IR and XRD. Pure single phase M-type hexagonal ferrites are formed at 800 °C. No secondary phase is evident from XRD. However, ND establishes small CoFe2O4 phase impurity at 0.6 level which increases at higher concentrations. MS and ND are employed to probe into the changes at the microscopic level. Dopant ions largely prefer 4f1 and 2a sites up to 0.6 level while substitution at 4f1 and 12k sites is indicated at higher concentrations. Contrary to the conventional thought Co2+ occupies the tetrahedral 4f1 sub-lattice while Zr4+ is located in an octahedral 2a/12k site. Magnetic hysteresis data show that the coercive force is reduced with increasing Co–Zr contents but the net magnetizations of the samples are not correlated with dopant level. Our results suggest that the magnetization and magneto-crystalline anisotropy are closely related to the distribution of Co–Zr on the five sites.