Effect of Dopants on the Magnetic Permeability and Dielectric Constant of Spinel Ferrites

Coatings made of materials that can efficiently absorb radiation, e.g., ferrite materials, are used to reduce the level of electromagnetic radiation in rooms containing household or industrial equipment. It is known that significant dissipation of the radiation energy can be provided by the thickness of the shielding coating which should be comparable to the electromagnetic wave length in the material, which, in turn, significantly decreases at high magnetic permeability and dielectric constant inherent in a radiofrequency-absorbing material. Radiofrequency-absorbing ferrite coatings are characterized by a high level of heat resistance, a low level of flammability, and a small (10–20 mm) thickness. However, at frequencies less than 40 MHz, the plate thickness should be higher than 30 mm to provide an efficient absorption level. In this case, the weight and cost of such coatings exhibit a significant increase. This paper presents the results of studying the effect of sintering temperature and titanium, calcium, and bismuth oxide dopants exerted on the dielectric constant of Ni- and Mn-Zn radiofrequency-absorbing ferrites. Reagent grade starting oxide components with a content of basic substance higher than 99.6 wt % have been used to synthesize samples on the basis of traditional oxide technology. It is shown that alloying with bismuth and titanium oxides is rather efficient for obtaining radiofrequency-absorbing ferrites that combine a high level of magnetic permeability and high dielectric constant. The obtained results can be used in the manufacture of radiofrequency-absorbing ferrite materials operating in the megahertz range.