Theoretical and experimental revelation of structural, dielectric, optical and magnetic properties of Sr1-xNixFe8SnO15 (x = 0, 0.2, 0.4, 0.6) V-type hexagonal ferrites

Abstract

A novel V-type hexaferrite with substitution of strontium by divalent Nickel, having the chemical formula Sr1-xNixFe8SnO15 (x = 0.0, 0.2, 0.4, 0.6), has been synthesized by employing the sol-gel auto combustion method. The X-Rays diffraction (XRD) patterns confirmed the hexagonal phase for all the samples however an extra peak due to SnO2 was also observed in XRD patterns. With the increase in Ni2+ concentration, the values of lattice constants a (Å), c (Å) and unit cell volume decreased slightly, and the crystallite size was calculated for all the samples to vary in the range of 19 to 21 nm. The transmission electron microscopy (TEM) analysis of all the samples indicated the average particle size lies in the range of 70-110 nm. The samples have maximum dielectric constant (ε’) and minimum electrical modulus (M’) at low frequency (< 100 Hz), and when frequency gradually increased both the parameters stabilized and became constant, with real permittivity values of 61.4 to 37.4 between 1 kHz and 10 MHz, high values for hexaferrites. The AC conductivity increased exponentially with the increase in frequency while Ni content had little effect on these values. The polarization verses electric field (P-E) loops showed electrical polarizability, but represented a lossy behavior which lessened with increasing Ni2+ content. The optical band gap energy values were increased slightly with Ni2+ substitution over the unsubstituted sample. The saturation magnetization (Ms) increased with Ni substitution from 31.1 emu/g in the pure V ferrite to a maximum value of 43.6 emu/g for x = 0.4, and remanence magnetization (Mr) values were also significant. However, a drastic decrease in coercivity (Hc) was observed with Ni substitution, from a reasonably hard ferrite (Hc = 2218 Oe, 176.5 kA/m) for x = 0.2 to very soft ferrites with x= 0.4 and 0.6 (Hc around only 200 Oe, 16 kA/m, a ten-fold decrease). The small grain size, reasonable Ms, and great variation in Hc with x between hard and soft ferrites, while maintaining some Mr, signify that these V-type hexaferrites could also be interesting materials for potential spintronic, magnetic memory and microwave absorption applications.