Quantitative and qualitative aspects of Ni-substitution on various properties of nano-sized hexagonal ferrites

This study aims to examine the structural, optical, dielectric, electrical, and magnetic characteristics of divalent Ni²⁺ transition metal-doped T-type hexagonal ferrites Ca_2-xNi_xFe₈O₁₄ (x = 0.0, 0.2, 0.4, and 0.6) by adopting the sol–gel auto-combustion technique. The XRD patterns of prepared samples indicate the synthesis of a single-hexagonal crystalline phase. The variation of lattice parameters, unit cell volume, crystallite size, and dislocation density are probed against Ni²⁺ substitution. The lattice parameters are reduced by increasing the concentration of Ni²⁺. The crystallite size varies between 24 and 27 nm which is advantageous to obtain suitable signal/noise ratio in density-recording media applications. The dielectric constant, dielectric losses, and tangent loss exhibited the highest values at the lower-frequency range for pure and substituted samples. For higher substitution (i.e., x = 0.4, 0.6), the ac conductivity rises as frequency rises. The intensity of imaginary modulus peaks rises with the substitution of Ni²⁺ ions substitution. The particle morphology and phase structure are confirmed by TEM investigation, and the average particle size of material varies between 90 and 100 nm. The energy band gap increased from 4.27 to 4.33 eV with doping of Ni²⁺. The values of magnetic parameters like saturation magnetization, remanence magnetization, and coercivity improved with Ni additives. The samples exhibited the loosy behavior, confirmed from P–E loops, and this loosy behavior decreased with Ni²⁺-ions doping that verify the increase in the resistive character of prepared samples.