Iron-Oxide Magnetic Materials for Millimeter-Wave Absorption

High-performance electromagnetic-wave absorbers are required for the control of millimeter-wave spectra, which will play a big role in future 5G and 6G wireless networks. Traditional absorbing materials comprised of metals or soft ferrites have been developed but their lack of ability to absorb at extremely high frequencies continues to hinder their practical applications. Thus, this article briefly introduces several iron-oxide magnetic materials with millimeter-wave absorbing capability.

Structural, Optical and Electrical Properties of Cu0.6CoxZn0.4−xFe2O4 (x = 0.0, 0.1, 0.2, 0.3, 0.4) Soft Ferrites

A series of cobalt-inserted copper zinc ferrites, Cu0.6CoxZn0.4−xFe2O4 (x = 0.0, 0.1, 0.2, 0.3, 0.4) having cubic spinel structure were prepared by the coprecipitation method. Various characterization techniques, including XRD, FTIR, UV-vis and I–V were used to investigate structural optical and electrical properties, respectively. The lattice constant was observed to be decreased as smaller ionic radii Co2+ (0.74 Å) replaced the higher ionic radii Zn2+ (0.82 Å). The presence of tetrahedral and octahedral bands was confirmed by FTIR spectra. Optical bandgap energy was determined in the range of 4.44–2.05 eV for x = 0.0 to 0.4 nanoferrites, respectively. DC electrical resistivity was measured and showed an increasing trend (5.42 × 108 to 6.48 × 108 Ω·cm) with the addition of cobalt contents as cobalt is more conductive than zinc. The range of DC electrical resistivity (108 ohm-cm) makes these nanomaterials potential candidates for telecommunication devices.

Structural analysis of Cu substituted Ni\Zn in Ni-Zn Ferrite

Ni-Zn ferrites are soft ferrites basically popular for high-frequency devices. They have low coercivity, low permeability, and higher resistivity. These properties have their own benefits on one hand but on the other hand, we can make them more efficient by doping suitable elements in order for tuning their properties for other applications. It this work, highly conducting Cu is used for substituting Ni in Ni-Zn ferrites and prepared Ni0.5-xCuxZn0.5Fe2O4 (x = 0, 0.05, 0.1, 0.15 and 0.2) samples using the sol-gel auto-combustion process. We have studied their resulting structural parameter using X-ray Powder Diffraction (XRD) and Fourier Transform Infrared (FTIR) Spectroscopy method and compared with that of Cu substituted Zn Ni-Zn ferrites. Their structures are found to be single-phase cubic spinel similar to that of Cu substituted Zn. The lattice constant increases with Cu concentration opposite to that at Zn substitution. Likewise, the size of the crystallites was not in monotonic change with the doping concentration in both cases due to internal strain and cation distribution. The difference in the pattern of XRD and FTIR of our samples indicate their different but significant properties. The changes in the structure show the effect of Cu doping and indicate the possible interesting changes in their electric, electronic, and magnetic properties. BIBECHANA 18 (2021) 128-133

Effect of Sr-substitution on the structural and magnetoelectric properties of Ni-Zn ferrites

Spinel type polycrystalline Ni0.6-xZn0.4SrxFe2O4 (x = 0.0, 0.05, 0.10, 0.15 and 0.20) ferrites are synthesized by solid state reaction method. X-ray diffraction (XRD) pattern reveals the formation of spinel structure with two secondary phases Sr2FeO4 and SrFe12O19 for higher concentration of Sr (0.15 and 0.20). An increase in lattice constant is observed with the increase of Sr content in the lattice. The density of the samples is found to decrease whereas porosity increases with the substitution of Sr2+ ions. Microstructural investigation shows that the grain size increases with the increase of Sr content. Magnetic hysteresis is investigated at room temperature. All the samples exhibit lower coercivity values indicating that the materials belong to the class of soft ferrites. The saturation magnetization is found to decrease with Sr content which is attributed to Néel’s two sub-lattice model of ferrites. The real permeability of the samples remains almost constant up to a certain frequency and then falls rapidly. Improved dielectric constant is observed in the Sr2+ substituted samples. The electrical conduction in these ferrites is explained on the basis of hopping mechanism between the Fe2+ and Fe3+ ions. Bangladesh Journal of Physics, 26(2), 1-20, December 2019