Enhancing high frequency magneto-dielectric performance with exchange-coupled garnet/spinel ferrite (Y3Fe5O12/Mg0.4Cd0.4Co0.2Fe2O4) composites

Abstract

Yttrium iron garnet ferrite (YIG), with good magnetic and dielectric properties, was mixed with doped magnesium spinel ferrite (Y3Fe5O12(x)/Mg0.4Cd0.4Co0.2Fe2O4(1-x) (x = 0.3, 0.6, 0.9)) to attain high permittivity and permeability with low magneto-dielectric losses. We have reported the synthesis and enhanced structural, magnetic and magnetodielectric properties of composites for miniaturized antenna applications. The X-ray diffraction (XRD) patterns of all the composites were analysed using the Rietveld method, which confirmed that they exhibited a crystalline structure with a cubic spinel and cubic garnet phase. XRD spectra confirm that the spinel ferrite phase dominates over the garnet ferrite phase in the x = 0.3 composite, whereas it is the opposite for the other composites. In contrast to the parent ferrites, it has been observed that the composites (x = 0.3, 0.6, 0.9) exhibit a higher value of the crystallite size ‘D’ and a lower value of the lattice constant ‘a’. The composite with the x = 0.3 composition has the least porosity and a high relative density. From field emission scanning electron microscopy (FESEM), it has been ascertained that the materials possess a grain size ranging from 0.57 to 0.8μm, with a larger grain size for the x = 0.9 composite, while the x = 0.3 composite has the smallest grain size. Transmission electron microscopy (TEM) scans have corroborated the FESEM micrographs’ findings, indicating that the grains within the composites’ structure exhibit agglomeration. The calculated values of inter-planar spacing of the samples using high-resolution TEM (HR-TEM) matches well with the XRD results. A magnetic study reveals that the composite with x = 0.3 has a good exchange-coupling, the highest coercivity value of 99.2 Oe and a magnetization value of 41 emu/g. The composite with x = 0.3 also has the highest permittivity value of ∼19.5, a permeability value of ∼2.8, but low dielectric and magnetic losses of ∼0.009 and ∼0.002, respectively. These low losses and a high miniaturization factor of ∼7.2 at high frequency (14 GHz) make it a potential candidate for high-speed satellite antenna applications.