Abstract
Mg-Ti substituted Ni-Zn spinel ferrites (Ni0.5Zn0.5MgxTixFe2−2xO4, where 0.05≤x≤0.25) have been prepared by conventional solid state reaction method. 1wt% B2O3 was added to increase the crystal growth at low temperatures. The structural characterization of samples was performed by X-ray powder diffractometry, scanning electron microscopy and Mössbauer spectroscopy. Magnetic parameters of samples were measured by vibrating sample magnetometer at room temperature. Microwave characteristics were determined by near field measurements using a network analyzer in reflection/transmission mode. Mössbauer spectra of all the samples consist of 3 sextets and one doublet. Variation of the line width, isomer shift, quadrupole splitting and hyperfine magnetic field values have been obtained from the 57Fe Mössbauer spectroscopy data for Ni-Zn spinels having different Mg2+ and Ti4+ concentrations. The saturation magnetization of the samples decreases as the concentration of Mg-Ti ions increases, which can be explained by site preferences of the substituted cations. The electrical properties of Mg-Ti substituted Ni-Zn spinel ferrites were examined extensively as a function of temperature, frequency and Mg-Ti amount. It was found that Mg-Ti substitution has a strong effect on the ac conductivity, dielectric constant and dielectric loss mechanisms. The activation energy levels can be regulated by varying Mg-Ti concentration. There is one reflection minimum observed in the microwave characterization of the samples in the 2–18GHz range located around 10GHz in X-band, the mechanism of which is the quarter wave cancellation due to the matching thickness. The Ni0.5Zn0.5Mg0.2Ti0.2Fe1.6O4 sample has the best microwave properties with the reflection loss of −29dB at 10.4GHz for a thickness of 3mm and better than −35dB at 16GHz when thickness is decreased to 2mm. As a result, it was concluded that this material can be used as microwave absorber both in X and Ku-bands.
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