Effect of zinc substitution on U-type barium hexaferrite-epoxy composites as designed for microwave absorbing applications

Abstract

In the current study, U-type barium hexaferrite (BHF) poly-crystalline powder with chemical formula Ba4Co2−xZnxFe36O60 (0.5 ≤ x ≤ 1.5 in step of 0.5) were successfully synthesized by solid state reaction route at the sintering temperature of 1400 °C in air medium. The effect of Zn+2 substitutions on the crystalline structural and magnetic properties of BHF powders were examined through nondestructive X-ray diffraction (XRD) technique and vibrating sample magnetometer (VSM) respectively. Upon increasing Zn+2 content the lattice parameters a and c decreases which is leading to the X-ray density up to a small degree, due to a smaller ionic size of Zn+2 as compared to Co+2 ions and saturation magnetization (Ms) from 56.08 emu/g for the zinc substituted sample down to 54.79 emu/g was observed. The transmission electron microscope (TEM) depicted that the particle size reached a minimum at x = 0.5 and then grown with x = 1.5 zinc content, getting a value of 103.06 nm with hexagonal phase and finer grains having the size range of ~0.51–1.0 µm thick and 5 µm long which is confirmed by field emission scanning electron microscopy (FESEM). A series of BHF-epoxy composites has been further transformed into toroidal shaped composites with fix volume percentage (54.3 vol%) of BHF powder in epoxy matrix. Electromagnetic properties; complex permittivity (εr = ε′ − jε″) and complex permeability (μr = μ′ − jμ″) of the prepared composites were computed through coaxial measurement techniques by using an Agilent E8364B vector network analyzer. Minimum return loss (RLmin) was observed as −32.98 dB (maximum absorption " 99.92) for matching frequency 10.3 GHz of the absorber with thickness of 3.1 mm and the bandwidth achieved was 7.38 GHz. Absorption values for prepared composites have potential use as excellent microwave absorbers over the frequency band C-band, X-band and Ku-band.