Hexaferrite samples, in which lanthanum (La) and cCobalt (Co) have been substituted (Sr \({Co}_{1.5z}{La}_{0.5z}{Fe}_{12-2z}{O}_{19}\) ), were synthesized using the sol–gel combustion method. X-ray diffraction (XRD) measurements revealed that all the samples maintained a magnetoplumbite structure. Fourier-transform infrared (FTIR) spectroscopy showed an absorption peak within the IR range of 1000–380 cm−1, indicating vibrations likely attributed to Fe–O bonds. Substitution caused a non-linear decrement in grain size and the existence of grain clusters in z = 0.1 along with an increment in porosity. The calculated porosity from XRD was consistent with the porosity observed with scanning electron microscopy. Both the dielectric constant and loss tangent parameters were found to be decreased non-linearly with substitution in the low-frequency region. The AC conductivity value decreased from 9.09 × 10−4 to 1.10 × 10−4 Ω−1 m−1 at 2-MHz frequency with Co-La substitution. Non-Debye behavior was noted in all the samples by evaluating the electric moduli and impedance spectra. The conductivity relaxation was dominant over the dielectric relaxation in the samples.
