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The aim of this study is to investigate in-depth the effect of Co 2+ ions doping on ZnFe 2 O 4 nanoparticles in term of morphology, magnetic and optical properties. Zn 1-x Co x Fe 2 O 4 (x = 0.0, 0.1, 0.2, 0.3, 0.4, 0.5) powders were prepared by co-precipitation method. X-ray diffraction (XRD) and Energy Dispersive Spectroscopy (EDS) confirmed the incorporation of Co 2+ ions within ZnFe 2 O 4 host lattice, and an increase of the crystallite size from 37 to 51 nm in agreement with TEM analysis. FTIR revealed a slight change in two main bands υ 1 and υ 2 in the frequency range of 400–4000 cm −1 , which caused by stretching vibrations at the A- and B-sites respectively. The elastic moduli such as stiffness constant, Young's modulus, rigidity modulus, bulk modulus, Poisson's ratio, wave velocity and Debye temperature have been calculated using FTIR data. VSM showed transformation of magnetic behavior from paramagnetic to ferromagnetic as a result of Co 2+ ions doping. With higher Co 2+ (x = 0.2 to x = 0.5) content, the saturation magnetization (Ms) increased rapidly from 5.7 emu/g to 82 emu/g respectively. The remanance magnetization (Mr) and coercivity (Hc) were influenced by Co 2+ content too and this was mainly related to the change in crystallite size. The optical band gap ( Eg ) of Co-Zn ferrite samples was determined by means of diffuse reflectance spectra. The optical band gap value estimated from Tauc plots was found to decrease from 1.89 to 1.31 eV with increasing Co 2+ content.

The cation distribution of the spinel system Zn1-xCoxFe2O4 (with x = 0; 0.1; 0.2; 0.3; 0.4; 0.5; 0.6; 0.7; 0.8; 0.9; 1.0) has been investigated by means of X-ray diffraction (XRD), Mossbauer spectroscopy and Fourier transform infrared spectroscopy (FTIR). In the present work, ferrites were prepared by co-precipitation method. XRD diffraction patterns show that all compositions have a pure single-phase cubic spinel structure over the whole composition range. It is found that both the lattice parameter and the average crystallite size decrease with increasing Co2+ content; from 8.4392 to 8.3536 A and from 37 to 25 nm for ZnFe2O4 and CoFe2O4, respectively. Morphological observations (SEM, TEM) reveal that the crystallinity decreases significantly with increasing Co2+ content meanwhile the particle size becomes more uniform. The elemental compositional stoichiometry have been carried out by means of energy dispersive analysis (EDS). The force constants Kt and Ko for the two sites have been deduced from IR band frequencies and compared with the trend of bond lengths: KT increases (from 2.084 to 2.144 dyn/cm2) because the bond length MA-O decreases, while KO decreases (from 1.043 to 0.948 dyn/cm2) because the bond length MB-O increases with increasing Co2+ content. For the first time antistructural modeling of zinc-cobalt ferrites considered. It shown that the acceptor in crystall latice is tetrahedral iron FeA , while the donor is octahedral cobalt Сo B ′ . With increasing Co2+ content, the concentration of active centers in tetrahedral and octahedral sublattice of zinc-cobalt ferrites are increases. The nature of the active centers are affecting on the chemical, electrical, magnetic, optical and catalytic properties of ferrites.