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Mixed spinel ferrites with stoichiometric equation NixZn1−xFe2O4 (x = 0.5, 0.6, 0.7) were synthesized by co-precipitation technique and consequently heat treated at 800 °C for 2 h. EDX spectra concluded the stoichiometry of elemental composition of present ferrite systems. Rietveld refinement of XRD patterns confirms the cubic spinel structure of the ferrite phase belonging to Fd3m space group. Lattice parameter (8.398–8.387 Å) is found to be in non-monotonic variation, whereas crystallite size (17.2–17.5 nm) is increased. From FE-SEM studies, the bigger ferrite nanoparticles (range of 27.9–39.4 nm) are found in the sample of composition x = 0.6. The variation of theoretical tetrahedral and octahedral bond lengths ( R A ′ and R B ′ ) is quite opposite to the variation of bond lengths (RA and RB) calculated from the Rietveld refinement. The vibrational frequencies in FTIR spectra (ranging from 592 to 385 cm−1) cope with the formation of spinel phase supporting the XRD results. The elastic moduli of present ferrite systems appears to be increasing, but these values are high for the composition x = 0.6. The isotropic nature of present ferrite systems has been revealed from the same value of Poisson ratio obtained for all compositions. [ABSTRACT FROM AUTHOR]