Effect of Co concentration on crystal structures and magnetic properties of Ni1-xCoxFe2O4 nanoparticles synthesized by co-precipitation method

Cobalt substituted nickel ferrite nanoparticles (Ni1-xCoxFe2O4) with stoichiometric proportion (x) from 0.2 to 0.8 have been synthesized by co-precipitation method with synthesis temperature of 90 degrees C. The crystallite size of Ni1-xCoxFe2O4 nanoparticles were within range of 14 - 27nm. The X-ray diffraction (XRD) analysis informed that the lattice parameter of Ni1-xCoxFe2O4 nanoparticles at x = 0.3 was 8.423 angstrom, and then increased with increasing Co concentration. This is due to substitution of larger ionic radius of Co2+. The selected area electron diffraction (SAED) patterns showed that increasing Co concentration exhibited more prominent ring indicating well crystallinity. It could be confirmed from the crystallinity of the sample for x = 0.7 was higher than 0.5. The SAED patterns of Ni1-xCoxFe2O4 nanoparticles also displayed polycrystalline diffraction ring. The fourier transform infrared spectroscopy (FTIR) spectra of Ni1-xCoxFe2O4 showed the presence of vibration bands of metal ions within the range of 370.33cm(-1) - 601.79cm(-1) at the tetrahedral and octahedral sites, respectively. These two bands indicated the formation of a spinel ferrite structure. The magnetic hysteresis results showed that the maximum magnetization at 15 kOe of Ni1-xCoxFe2O4 nanoparticles at x = 0.2 was 7.0emu/g, and then increase to 29.0emu/g at x = 0.8 with increasing Co concentration. The results could be attributed to substitution of higher magnetic moment of Co2+. The coercivity (H-c) of Ni1-xCoxFe2O4 nanoparticles at x = 0.2 was 59.4Oe, and then increase to 641.75Oe at x = 0.6 with increasing Co concentration. This is due to cobalt having higher magnetic anisotropy than nickel.