Magnetic and High-Frequency Dielectric Parameters of Divalent Ion-Substituted W-Type Hexagonal Ferrites

Abstract

Polycrystalline W-type hexagonal ferrites with chemical formulae Ba_0.5Sr_0.5 Co_2−x Me _x Fe₁₆O₂₇ (x = 0, 0.5, Me = Mn, Mg, Zn, Ni) have been prepared using sol–gel autocombustion. It has been reported in our earlier published work that all the samples exhibit a single-phase W-type hexagonal structure which was confirmed by x-ray diffraction (XRD) analysis. The values of bulk density lie in the range of 4.64–4.78 g/cm³ for all the samples which are quite high as compared to those for other types of hexaferrites. It was also observed that Zn-substituted ferrite reflects the highest (14.7 × 10⁷ Ω-cm) whereas Mn-substituted ferrite has the lowest (11.3 × 10⁷ Ω-cm) values of direct current (DC) electrical resistivity. The observed values of saturation magnetization (M _s) are found to be in the range of 62.01–68.7 emu/g depending upon the type of cation substitution into the hexagonal lattice. All the samples exhibit a typical soft magnetic character with low values of coercivity (H _c) that are in the range of 26–85 Oe. These ferrites may be promising materials for microwave absorbers due to their higher saturation magnetization and low coercivities. Both the dielectric constant and tangent loss decrease with increasing frequency in the lower frequency region and become constant in the higher frequency region. The much lower dielectric constant obtained in this study makes the investigated ferrites very useful for high-frequency applications, i.e. dielectric resonators and for camouflaging military targets such as ships, tanks and aircrafts, etc.