Evaluations of structural, magnetic and various dielectric parameters of Ni-substituted Zn2W-type hexagonal ferrites for high frequency (1–6 GHz) applications

Abstract

The structural, electrical, magnetic and high frequency properties of Ni-substituted Zn2W-type hexagonal ferrites were investigated for microwave applications. Ferrite powders with chemical compositions Ba0·5Sr0.5NixZn2-xFe16O27 (where Ni-substitution was varied from 0.0 to 1.5 with a step size of 0.5) were prepared using sol-gel auto-combustion at 1300 °C. X-ray diffraction (XRD) analysis confirmed the single-phase hexagonal ferrite structure. The lengths of both the axis i.e. minor and major (a, c) obtained from hkl values of XRD peaks were decreased with Ni-substitution due to the difference in ionic radius of the substituted metal ions. DC electrical resistivity obtained by two-point probe method increased with Ni-substitution. Scanning electron microscopy (SEM) showed hexagonal plate-let like structure. Fourier transform infrared (FT-IR) spectroscopy showed two characteristic bands corresponding to metal-ion stretching vibrations. Vibrating sample magnetometer (VSM) results showed thin S-shaped M − H curves with high saturation magnetization and low magnetic coercivity for all substituted samples. Vector network analyzer (VNA) was used to investigate the high frequency parameters of both dielectric and magnetic type. The real part of permittivity and permeability decreased with increasing frequency whereas variation in imaginary part of both the parameters was negligible. The magnetic losses were decreased appreciably to 0.1 with Ni-substitutions. Microwave absorbance linked with loss tangent was found to increase whereas relaxation peaks shifted to high frequencies with Ni-substitution. It was found that Ni-substituted Zn2W-type hexagonal ferrites were suitable for the microwave absorbing applications in1–6 GHz frequency range.