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A series of single-phase spinel cubic structure Mn-Zn ferrites with the general formula MnMgZn FeO were prepared by a ceramic method. Mg content improves the crystallinity of Mn-Zn ferrites. The formula of the cation distribution for Mn-Zn ferrites was suggested at different Mg contents showing a good agreement between the theoretical and experimental structural data. The bulk density of the samples decreases by increasing the Mg content. The porosity of ferrite samples is increased from 16.7 to 19% by increasing the Mg content. Scanning electron microscopy (SEM) reveals that the grain diameter of Mn-Zn system decreases with Mg content. ESR measurements show that the resonance field, line width, and dielectric loss increase with Mg content. On the contrary, splitting factor and experimental magnetic moment decrease with Mg content. Thermo-electric power measurements indicate that the preponderance carriers are holes and localized to the lattice. The change of structure and properties of the ferrite samples are accurately observed with high sensitivity using positron annihilation spectroscopy (PAS) techniques. The results reveal that there are strong correlations between the PAS parameters and some parameters of ESR. It is suggested that PAS can be exploited as a powerful technique for characterizing magnetic material such as ferrite systems. [ABSTRACT FROM AUTHOR]

In this paper, an efficient lightweight double-layer microwave absorber with impedance-matching structure at X-Ku bands was designed, optimized and implemented. First, genetic algorithm GA) was considered to optimize the thicknesses and material properties for better absorption of the incident electromagnetic wave and reduction of radar cross section (RCS). Next, with the aid of the obtained dielectric and magnetic properties, the microwave absorber was fabricated from magneto-dielectric composite materials besides a natural rubber. Finally, the analytical and numerical results were compared with the measurements to check the validity of the design. Experiments showed that the reflection coefficient for each layer backed with a metallic sheet was insufficient; however, for the double layer absorber, the reflectivity measurement values reached up to -28 dB in the case of normal incidence and -17 dB for oblique incidence. [ABSTRACT FROM AUTHOR]