Nickel ferrite has been synthesized by microwave and auto combustion method. Crystal structure has been confirmed by XRD. The FT-IR spectra of synthesized ferrites showed two absorption bands (Î½1 and Î½2) in the range 400â€“600 cmâ€“1 belonging to tetrahedral (A) and octahedral (B) interstitial sites in the spinel lattice. From Fourier transform infrared spectroscopy, stiffness constants (for isotropic material, C11=C12), longitudinal elastic wave (Vl), transverse elastic wave
(Vt), mean elastic velocity (VMean), rigidity modulus (G), Poissonâ€™s ratio(s) and Youngâ€™s modulus (E) of ferrites has been computed and compared by these two methods.