Co-doped spinel-ferrites Ni1-xCoxFe2O4 nanoparticles with an average diameter of 16-40 nm were successfully prepared by co-precipitation method. The lattice parameter of Co-doped spinal-ferrites Ni (1-x) Co(x) Fe2O4 nanoparticles as well as the porosity was found to decrease while the density and grain size increased with increasing the Co concentration (x). The cation distribution has been estimated by X-ray diffraction. The process of functional group has been identified by Fourier transform infrared (FTIR) spectra and the force constants are calculated from these spectra. Thermal behavior...