Dysporium (Dy)-substituted W-type barium hexaferrites were prepared by the citrate sol-gel-method. Crystalline structure, morphology, magnetic properties, DC resistivity and microwave absorption properties of BaNi 2 Dy x Fe 16−x O 27 (x = 0-0.9) were studied using X-ray diffraction, transmission electron microscope (TEM), vibrating sample magnetometer and vector network analyzer and sensitive source meter, respectively. Single-phase W-type barium hexaferrites, with a chemical composition of BaNi 2 Dy x Fe 16−x O 27 (x = 0-0.9), were formed by being heated at 1250 • C for 4 h in air. The magnetic properties such as saturation magnetization (M s ), and coercivity (H c ) were calculated from hysteresis loops. Hysteresis loop measurements show that the coercivity values lie in the range of 530-560 Oe with increasing Dy content. It was also observed that magnetization decreases with the increase of Dy content. The DC resistivity was observed to increase from 0.83 × 10 7 to 6.92 × 10 7 cm with increasing Dy contents due to the unavailability of Fe 3+ ions. Microwave absorption properties of hexaferrite (70 wt%)-acrylic resin (30 wt%) composites were measured by the standing-wave-ratio (SWR) method in the range from 12 to 20 GHz. For sample with x = 0.6, a minimum reflection loss of −40 dB was obtained at 16.2 GHz for a layer of 1.7 mm in thickness. Sample with x = 0.9 had wide bandwidth absorption in the frequency range of 13.5-18 GHz with reflection losses less than −15 dB. Meanwhile the minimum reflection point shifts toward higher frequency with the increase of Dy content.

Nanoparticles of Ca(MnSn) x Fe 12À2x O 19 with x ranging from 0.00 to 0.6 in steps of 0.2 were prepared by use of the citrate precursor method. The structural, microwave-absorption, and magnetic properties of these ferrites were determined by use of different characterization techniques. The morphology of the ferrite powders was investigated by transmission electron microscopy (TEM). X-ray diffraction (XRD) was used for structural and micro-structural studies, and revealed that the samples had an M-type hexagonal structure. The crystallite size for each sample was calculated by use of the Scherrer formula for the most intense peak (411) and the results were compared with those obtained from TEM images of the samples. The particle size of the powder varied from 60 to 36 nm. Magnetic measurements were performed by vibrating sample magnetometry (VSM) at room temperature. The microwaveabsorption properties of ferrite (70 wt.%)-polymer (30 wt.%) composites 2 mm thick were investigated by vector network analysis (VNA) in the frequency range 12-20 GHz. The ferrite for which x = 0.4 had a minimum reflection loss of À29 dB at 17.3 GHz with a À15 dB bandwidth over the extended frequency ranges 12.9-14.5 GHz and 16.7-18 GHz. The minimum loss reached À32 dB at frequency of 17 GHz when the total amount of Mn 2+ and Sn 4+ ions was 0.6. These results suggest that the synthesized magnetic composites can be used as effective microwave absorbers in military applications (radar cross-section reduction).

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