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

Abstract

A novel V-type hexaferrite with the substitution of strontium by divalent nickel, having the chemical formula Sr_1−xNi_xFe₈SnO₁₅ (x = 0.0, 0.2, 0.4, and 0.6), is synthesized by employing a sol–gel auto combustion method. X-ray diffraction (XRD) patterns confirmed the hexagonal phase for all the samples; however, an extra peak due to SnO₂ was observed. With the increase in the Ni²⁺ concentration, the values of lattice constants a (Å) and c (Å) and unit cell volume decreased slightly, and the crystallite size was calculated to vary in the range of 19 to 21 nm for all the samples. Transmission electron microscopy (TEM) analysis indicated that the average particle size lies in the range of 70–110 nm for all the samples. The samples have the maximum dielectric constant (ε′) and minimum electrical modulus (M′) at low frequency (<100 Hz); when the frequency is gradually increased, both the parameters stabilized and became constant, with real permittivity values from 61.4 to 37.4 between 1 kHz and 10 MHz, which are high values for hexaferrites. AC conductivity increased exponentially with the increase in frequency, while Ni content had little effect on these values. The polarization versus electric field (P–E) loops showed electrical polarizability but represented a lossy behavior that lessened with increasing Ni²⁺ content. The optical band gap energy values increased slightly with Ni²⁺ substitution over the unsubstituted sample. The saturation magnetization (M_s) increased with Ni substitution from 31.1 emu g⁻¹ in the pure V ferrite to a maximum value of 43.6 emu g⁻¹ for x = 0.4, and remanence magnetization (M_r) values were also significant. However, a drastic decrease in coercivity (H_c) was observed with Ni substitution, from a reasonably hard ferrite (H_c = 2218 Oe, 176.5 kA m⁻¹) for x = 0.2 to very soft ferrites with x = 0.4 and 0.6 (H_c of around only 200 Oe, 16 kA m⁻¹, a ten-fold decrease). The small grain size, reasonable M_s, and great variation in H_c with x between hard and soft ferrites while maintaining some M_r signify that these V-type hexaferrites could also be interesting materials for potential spintronic, magnetic memory, and microwave absorption applications.