Investigation of electrical, dielectric, and relaxation metrics of SrFe${}_{12}$O${}_{19}$/Fe${}_3$O${}_4$ hexaferrite composites

In this work, composites were prepared from La-Co-doped strontium ferrite (SrFe${}_{12}$O${}_{19}$) and soft magnetite (Fe${}_3$O${}_4$) in a 1:5 weight ratio, spanning a range of substitutions from z = 0.0 to 0.5. The X-ray diffraction analysis of all prepared composites revealed the co-existence of hard (M-type) and soft (spinel) ferrite phases. Notably, in z = 0.0 (20% Fe${}_3$O${}_4$ of SrFe${}_{12}$O${}_{19}$) a minor trace of α-Fe${}_2$O${}_4$ was observed. Field emission scanning electron microscopy (FESEM) micrographs displayed distinct particles of M-type and spinel ferrite at z = 0.0, and substitution rendered a change in grain/grain size distribution. Composition z = 0.4 exhibited the highest dielectric constant, which can be correlated with the maximum grain boundary capacitance C${}_{gb}$ (29.77 µF) calculated from impedance spectroscopy software. In contrast, z = 0.3 revealed the maximum conductivity relaxation and explained through the dense/closely packed grains observed in micrographs. The replacement of Fe${}^{3+}$ ions with Co-La ions caused a reduction in conductivity value and was maximum for z = 0.4 (3.26 × 10${}^{-5}$ Ω${}^{-1}$ m${}^{-1}$) in the high-frequency region. A segment of a semicircular arc had been observed in all synthesized composites in Z${}^{\prime \prime }$ vs. Z${}^{\prime }$ Cole-Cole plots. This observation indicated a significant enhancement in dielectric relaxation brought about by the Co-La substitution.