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The sol gel method has been adopted to synthesize a series of X-type hexagonal ferrites with concentration Sr 2− x Gd x Ni 2 Fe 28− y Cd y O 46 ( x =0.00, 0.02, 0.04, 0.06, 0.08, 0.10 and y =0, 0.1, 0.2, 0.3, 0.4, 0.5). The XRD analysis reveals the single phase of the prepared material and the lattice constants a (Å) and c (Å) varies with additives. The crystallite size of the present investigated ferrite is found in the range of 20–30 nm measured from TEM image. The enhancement in the magnetic properties (saturation magnetization, remanance magnetization and coercivity) can be observed with the increase of dopping concentration and the coercivity lies in the range of (484.22–887.47) G. The saturation and remanance magnetization decreases monotonically with the temperature which is the characteristic of the hexagonal ferrites. The Gd–Cd substituted sample possesses low values of complex relative permittivity and permeability than the pure samples. The material exhibits maximum microwave absorption −23 dB at 11.87 GHz and attenuation peak is in good agreement with the reflection loss value. The microwave absorption properties reflect the applications of this material in super high frequency devices (SHF). [ABSTRACT FROM AUTHOR]

A series of single phase spinel ferrites having chemical formula Mg 0.5 Zn 0.5 Pr x Fe 2− x O 4 ( x =0.00, 0.05, 0.10, 0.15, 0.20, 0.25) were prepared using the sol–gel technique after sintering at 700 °C. The thermal decomposition behavior of an as prepared powder was investigated by means of DTA/TGA analyses. The sintered powders were then characterized by Fourier transform infrared spectroscope, X-ray diffraction, scanning electron microscope, energy dispersive X-ray spectroscope and vibrating sample magnetometer. X-ray diffraction patterns confirm the single phase spinel structure of prepared ferrites without the presence of any impurity phase. The value of lattice parameter ( a ) increases with the increase of Pr contents ( x ) into the spinel lattice. The grain size estimated from electron microscope images is in the range of 2.75–5.4 µm which confirms the spinel crystalline nature of the investigated samples. The saturation magnetization ( M s ) decreases whereas coercivity ( H c ) increases with the increase of Pr contents ( x ). The measured parameters suggest that these materials are favorable for high frequency applications and as core materials. [ABSTRACT FROM AUTHOR]

Highlights: [•] W-type hexagonal ferrites substituted with different divalent ions have been investigated. [•] Platelets like grains with hexagonal shape are suitable for microwave absorbers. [•] Saturation magnetization was calculated by the law of approach to saturation. [•] The low value of coercivity for the investigated sample is favorable for EM materials. [•] The materials are good for suppression of EMI and as radar absorbing materials (RAMs). [ABSTRACT FROM AUTHOR]

Abstract: The magnetic and microwave characterization of single phase hexaferrites of entirely new composition Ba1-x Sr x Co2AlFe15O27 (x=0.2–1.0) for application in a microwave absorber, have been reported. The samples synthesized by sol–gel method were investigated by differential thermal analyzer, Fourier transform infrared spectroscope, X-ray diffractometer, field emission gun scanning electron microscope, vibrating sample magnetometer and vector network analyzer. Platelet grains exhibit well defined hexagonal shape which is a better shape for microwave absorption. M–H loops for a selected sample were measured for a temperature range of 4.2–400K. Moreover M–H loops for all Sr-substituted samples were also measured at room temperature up to a maximum applied field of 9T. Saturation magnetization values were calculated by the law of approach to saturation. The room temperature coercivity for all the samples is found to be a few hundred oersteds which is necessary for electromagnetic materials and makes these ferrites ideal for microwave devices, security, switching and sensing applications. The complex permittivity, permeability and reflection losses of a selected ferrite–epoxy composite were also investigated over a frequency range of 0.5–13GHz. [Copyright &y& Elsevier]