The rapid increase in electromagnetic interference has received a serious attention from researchers who responded by producing a variety of radar absorbing materials especially at high gigahertz frequencies. Ongoing investigation is being carried out in order to find the best absorbing materials which can fulfill the requirements for smart absorbing materials which are lightweight, broad bandwidth absorption, stronger absorption etc. Thus, to improve the absorbing capability, several important parameters need to be taken into consideration such as filler type, loading level, type of polymer matrix, physical thickness, grain sizes, layers and bandwidth. Therefore, this article introduces the electromagnetic wave absorption mechanisms and then reveals and reviews those parameters that enhance the absorption performance.

Crystalline zinc ferrite (ZnFe2O4) was prepared by the thermal treatment method, followed by calcination at various temperatures from 723 to 873 K. Poly (vinyl pyrrolidon) (PVP) was used as a capping agent to stabilize the particles and prevent them from agglomeration. The characterization studies were conducted by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The average particle sizes of 1731 nm were obtained by TEM images, which were in good agreement with the XRD results. Fourier transform infrared spectroscopy (FT-IR) confirmed the presence of metal oxide bands at all temperatures and the absence of organic bands at 873 K. The magnetic properties were demonstrated by a vibrating sample magnetometer (VSM), which displayed super paramagnetic behaviors for the calcined samples. The present study also substantiated that, in ferrites, the values of the quantities that were acquired by VSM, such as the saturation magnetization and coercivity field, are primarily dependent on the methods of preparation of the ferrites. Electron paramagnetic resonance (EPR) spectroscopy showed the existence of unpaired electrons and measured the peak-to-peak line width (Δ Hpp), the resonant magnetic field (Hr), and the gfactor values.

Nickel ferrite nanocrystals were prepared from an aqueous solution containing metal nitrates and poly (vinyl pyrrolidone) (PVP) as a capping agent. To stabilize the particles, they were thermally treated at various temperatures from 623 to 823. K at which calcination occurred, thereby stabilizing the particles, controlling the growth of the nanoparticles, preventing their agglomeration, and creating a uniform distribution of particle sizes. The characterization studies were conducted by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and transmission electron microscopy (TEM). The crystallization was completed between 723 and 823. K, as revealed by the absence of organic absorption bands in the FT-IR spectra Magnetization measurements were obtained at room temperature by using a vibrating sample magnetometer (VSM), which showed that the calcined samples exhibited ferromagnetic behaviors. Finally, we used TEM images and FT-IR spectra to investigate the same process in the absence of PVP and with various of concentrations of PVP for comparison with the results acquired from using the optimum concentration that was used in this work.

Nanosized cobalt ferrite spinel particles have been prepared by using mechanically alloyed nanoparticles. The effects of various preparation parameters on the crystallite size of cobalt ferrite which includes milling time; ball-to powder weight ratio (BPR) and sintering temperature, were studied using X-ray diffractometer (XRD). Scherrer's equation was used to study the crystallite size evolution of the as-prepared materials. The results of the as-milled sample revealed that both milling time and BPR plays a role in determining the crystallite size of the milled powder. However, where sintering is involved, the sintering temperature results in grain growth, and thus plays a dominant role in determining the final crystallite size of the samples sintered at higher temperature (above 900 °C). From the vibrating-sample magnetometer (VSM) measurement it was observed that the coercivity of the as-milled samples without sintering is almost negligible, which is a type characteristic of superparamagnetic material. However, for the sintered samples, the saturation increases while coercivity decreases with increases sintering temperature.

Nanocrystalline magnesium ferrites (MgFe2O4) were produced with an average grain size of about 20 nm. Their structural, morphological, and magnetic characterizations were studied. The cytotoxic effects of MgFe2O4nanoparticles in various concentrations (25, 50, 100, 200, 400, and 800 μg/mL) against MCF-7 human breast cancer cells were analyzed. MTT assay findings suggest the increased accumulation of apoptotic bodies with the increasing concentration of MgFe2O4nanoparticles in a dose-dependent manner. Flow cytometry analysis shows that MgFe2O4nanoparticles in 800 μg/mL concentration are more cytotoxic compared to vehicle-treated MCF-7 cells and suggests their potential utility as a drug carrier in the treatment of cancer.

In the study, the Ni-Zn ferrite powder of a Ni 0.3 Zn 0.7 Fe 2 O 4 composition was synthesized by sol-gel route using metal acetates at low temperatures. Both the scanning electron microscope and X-ray diffraction analyses of various gel samples heated at different temperatures were used to identify the reaction stages where the amorphous-gel-to-crystalline phase transition occurred. The electrical, magnetic and microstructural properties of the toroidal cores were studied. It was found that the initial permeability increased with a large frequency band (0.1-31.39 MHz) and the magnetic loss was small. The electrical resistivity was higher as compared to the ones which were obtained by the conventional process. Therefore, well-defined polycrystalline microstructure nickel-zinc ferrite and a short processing time of gel preparation have become the major achievements of this study. r

Crystalline, magnetic, cobalt ferrite nanoparticles were synthesized from an aqueous solution containing metal nitrates and polyvinyl pyrrolidone (PVP) as a capping agent by a thermal treatment followed by calcination at various temperatures from 673 to 923 K. The structural characteristics of the calcined samples were determined by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and transmission electron microscopy (TEM). A completed crystallization occurred at 823 and 923 K, as shown by the absence of organic absorption bands in the FT-IR spectrum. Magnetization measurements were obtained at room temperature by using a vibrating sample magnetometer (VSM), which showed that the calcined samples exhibited typical magnetic behaviors.

Calcium titanate (CaTiO3) with the general formula for perovskites, ABO3, is of technological importance, particularly with regard to dielectric properties. In this work, CaTiO3 ceramic material was prepared by the conventional solid state reaction method. The dielectric properties, impedance characteristics and modulus behavior of the CaTiO3 ceramic material sintered at 1240 °C were investigated in the frequency range of 10−2-106 Hz and temperature range of 100-250 °C. The XRD analysis of the sintered CaTiO3 shows that it is an orthorhombic structure with lattice parameters a = 5.4398 Å, b = 7.6417 Å, and c = 5.3830 Å. The FESEM micrograph shows a significant difference in grain size distribution ranging from 0.26 to 2.32 μm. The AC conductivity, σAC, is found to increase with increasing temperature within the frequency range of 10−2-106 Hz confirming the hopping of electrons to be the conduction mechanism. Due to the decreasing values of the frequency exponent s with increasing temperature, the results of the σAC are discussed using the correlated barrier height (CBH) model. For dielectric studies, the dielectric constant, ε′ is found to decrease with increasing frequency. In the whole temperature range of 100-250 °C, high and low frequency plateau are observed. Each converges at high frequency (>105 Hz) for all the temperatures. The frequency dependence of loss tangent, tan δ, decreases with rise in temperature, with the loss tangent peak shifting to higher frequency. Due to its dielectric characteristics, it is a suitable candidate for developing a variety of capacitors. For the master modulus plot, the shapes remain unchanged in the temperature range considered. The Cole-Cole plots reveal that two primary relaxation processes exist in the sample for each temperature. The Nyquist plots reveal that at temperatures below 150 °C, a linear response in the imaginary part of the impedance, Z′′, is noticed. At and above 175 °C, the linear response gradually changes to a semicircle arc. The modulus behavior indicates the presence of correlation between the motions of mobile charge carriers. The plots of Arrhenius diagram of relaxation times of loss tangent, τtanδ, and imaginary part of dielectric modulus, τM′′, obey the Arrhenius law, where the activation energies calculated from the slopes are 2.09 and 2.38 eV respectively.