Comparison of K_u (12.4–18 GHz) and K (18–26.5 GHz) Band Microwave Absorption Characterization of Co-Zr Co-substituted Ni-Zn Ferrites

The microwave absorption behaviour of nano-scale cobalt-zirconium co-substituted nickel-zinc ferrites Ni_0.6Zn_0.4(CoZr)_xFe_2-2xO₄ (x = 0.05, 0.10, 0.15, 0.20 and 0.25) synthesized via a sol–gel citrate precursor is reported in K_u (12.4-18 GHz) and K (18-26.5 GHz) band frequencies. The dielectric characterization of the ferrites exhibits that values of real permittivity (ε′) decrease over the range of K_u band frequencies but less dispersion is found in the K band. Dielectric losses are found to be maximum in composition Ni_0.6Zn_0.4(CoZr)_0.25Fe_1.5O_4. The magnetic characterization exhibits that real permeability (μ′) has a constant trend over the increasing range of frequencies but prominent peaks are observed in the spectra of imaginary permeability (μ″). Highest magnetic losses are observed for composition Ni_0.6Zn_0.4(CoZr)_0.25Fe_1.5O₄ similar to dielectric losses_. The reflection loss (RL) minima of −42.83 dB at 16.992 GHz and −26 dB at 18.68 GHz is found for the same composition in K_u and K band, respectively, with a matching thickness of 2 mm.