Synthesis and role of structural disorder on the optical, magnetic and dielectric properties of Zn doped NiFe2O4 nanoferrites

Abstract

Nanoferrites of the chemical formula Ni1-xZnxFe2O4 (0 ≤ x ≤ 0.6) were synthesized via the sol-gel auto combustion process. All the samples were extensively characterized to explore the influence of zinc doping on several physical properties. The detailed analysis of the XRD data confirms the cubic spinel structure of the compositions. The lattice constants and unit cell volume as computed by the Rietveld refinement program are found to follow the Vegard's law. Crystallite sizes of the samples as calculated through Scherrer equation and Williamson-Hall method decrease upon Zn doping in NiFe2O4. The formation of spinel phase was further confirmed by the characteristics bands in FTIR spectra. The well defined spherical morphology and narrow size distribution of the particles together with the purity of synthesized samples were examined by the scanning electron microscopy (SEM) along with energy dispersive x-ray (EDX) analysis. Raman spectra divulge the tetrahedral and octahedral sites in the structure and infer the successful Zn2+doping and replacement of Fe3+ ions from the tetrahedral sites. The optical bandgap and other parameters were calculated by the UV–visible absorption spectra that reveal considerable increase in the band gap of the samples on account of Zn doping. The frequency dependent dielectric investigations show distinct behavior of dielectric constant and an increase in loss tangent on increasing zinc concentration. The ac conductivity enhances with the increase in dopant concentration and attributed to the electron-hole hopping mechanism. The Nyquist plots revealed incomplete and partial semicircular curves for all compositions, signifying a non-Debye type of relaxation mechanism in the system. Field-dependent magnetization predicts ferromagnetic behavior with a narrower hysteresis loop for the samples of higher zinc concentration. An increase is observed in saturation magnetization (Ms) and coercivity (Hc) till 20% zinc content, while further doping reduces these parameters. This effect was elaborated by metal cations distribution into the tetrahedral and octahedral sites.