Ni-substituted Z-type hexaferrites with the chemical formula Sr3Co2-xNixFe24O41 (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5)
were prepared by solid-state reaction processes. XRD analysis revealed that nearly a single Z-type hexaferrite
phase could be obtained for the samples with Ni substitution x ≤ 0.5 when the samples were twice calcined at
1160 and 1235 °C, respectively, in air. The complex permittivity (ε', ε") and permeability (μ', μ") spectra (100
MHz ≤ f ≤ 18 GHz) and electromagnetic (EM) wave absorption properties were studied on Sr3Co2-xNixFe24O41
(x = 0, 0.1, 0.2, 0.3, 0.4, 0.5) powder-epoxy (10 wt%) composites. The permeability spectra continuously shifted
to a lower frequency with an increase in x, owing to the decrease in the magnetocrystalline anisotropy. The
peak frequency of μ" gradually decreased from 3.2 GHz to 2.0 GHz, and in turn, it shifted the corresponding
EM absorption frequency range. The frequency corresponding to the minimum RL peak point also decreased
from 3.3 GHz to 2.3 GH with an increase in x from 0 to 0.5. All the samples exhibited the lowest reflection loss
of < -40 dB at the optimized frequency and thickness. The study shows that Ni substitution is very effective for
the delicate tuning of electromagnetic absorption frequency in S-band (2-4 GHz).