LAUSR

A series of cobalt substituted nickel ferrite nanoparticles with nominal compositions, Ni(1−x)Co(x)Fe2O4 (x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) have been synthesized by gel process. The samples are characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM) and vibrating sample magnetometer. The XRD spectra revealed that all the samples are of single phase spinel structure and the average size of nanocrystallite was calculated for a sample by the full width at half maximum (FWHM) of the strongest XRD peak. These sizes are small enough to achieve the suitable signal to noise ratio for the high density recording media. The lattice constant (a), X-ray density (ρx) and cell volume (V) are also calculated from XRD data. Experimental, theoretical lattice constant (aexp, ath), tetrahedral and octahedral radii (rA and rB), tetrahedral and octahedral bond length (dAx and dBx), tetrahedral edge (dAxE), shared octahedral edge (dBxE) and unshared octahedral edge (dBxEU) of the annealed Ni–Co ferrite nanoparticles increase with the increase in Co doping. Morphology of the samples was investigated by a FE-SEM. The FTIR spectra of the spinel phase calcinated at 600 °C exhibit two prominent fundamental absorption bands in the range of 350–610 cm−1 assigned to the intrinsic stretching vibrations of the metal at the tetrahedral and octahedral sites. The specific saturation magnetization (Ms), remanent magnetization (Mr) and the coercivity (Hc) of the spinel ferrites are further improved by the substitutions of Co+2 ions. The values of Ms for NiFe2O4 and CoFe2O4 are found to be 60.92 and 70.59 emu/g, respectively and Hc are in the range of 452.12–1026 Oe. The process is investigated with simultaneous thermogravimetric-differential thermal analysis (TG–DTA). The role played by the Co ions in improving the structural and magnetic properties are analyzed and understood. Our simple, economic and environmental friendly preparation method may contribute towards the controlled growth of high quality ferrite nanopowders and a potential candidate for recording media application.