Effect of Zn²⁺-Zr⁴⁺ co-substitution on structural, magnetic and dielectric properties of Ba_0.5Ca_0.5Zn_xZr_xFe_12−2xO₁₉ hexaferrite

In present study, M-type hexaferrite, Ba_0.5Ca_0.5Zn_xZr_xFe_12−2xO₁₉ (x = 0.00–1.00 with increment of 0.2 per step) were fabricated by the conventional sol-gel technique. The powder X-ray diffraction (PXRD) patterns certified the exchange of Fe³⁺ ions by Zn²⁺-Zr⁴⁺ ions. Both the lattice parameters ‘a’ and ‘c’ have raised from 5.885 (x = 0.00) to 5.926 Å (x = 1.0), and from 23.091 (x = 0.00) to 23.455 Å (x = 1.00), respectively. FESEM micrographs display a slight drop in the size of grains with doping. The maximum saturation magnetization (M_S ≈73.31 emu/g) was detected for x = 0.2 configuration, that is larger than observed value of M_S of 72.0 emu/g for pure barium hexaferrite material. The value of coercivity (H_C) declines significantly from 2151 to 161 Oe with the increase of Zn²⁺-Zr⁴⁺ doping. Mössbauer spectra have been recorded to determine the preferential site occupancy by Zn²⁺-Zr⁴⁺ dopant ions and also the ionic state of Fe-ions. A Mössbauer spectrum shows a doublet and five sextets. All components are in a high spin state as a result of the Fe³⁺ ions. The magnetically hard material is converted into a magnetically soft one with the incorporation of Zn²⁺-Zr⁴⁺ dopants. The decreasing trend in M_s is also verified by the Mössbauer results. With Zn²⁺-Zr⁴⁺ co-substitution, the average values of hyperfine field (H_f) decrease from 46.5 (x = 0.0) to 36.9 T (x = 1.0), whereas the comparative size of paramagnetic doublet is increased from 0.5 (x = 0.00) to 12.6% (x = 1.00). These samples have superior saturation magnetization (45.42–71.50 emu/g) and coercivity (161–2151 Oe) with substitution, which can be vital for both low- and high-density magnetic recording media applications. From the dielectric measurements of Ba_0.5Ca_0.5Zn_xZr_xFe_12−2xO₁₉ (x = 0.0–1.0) hexaferrites, it was observed that the dielectric constant was improved as the Zn²⁺-Zr⁴⁺ co-substitution increased up to x = 0.80. After that, it started to go down for x = 0.20. In addition, the dielectric study suggests dielectric loss (tan δ) capability within the prepared hexaferrites which makes them also suitable for the EMI shielding application.