Effect of Co concentration on crystal structures and magnetic properties of Ni_1-xCo_xFe₂O₄ nanoparticles synthesized by co-precipitation method

ABSTRACT

Cobalt substituted nickel ferrite nanoparticles (Ni_1-xCo_xFe₂O₄) with stoichiometric proportion (x) from 0.2 to 0.8 have been synthesized by co-precipitation method with synthesis temperature of 90°C. The crystallite size of Ni_1-xCo_xFe₂O₄ nanoparticles were within range of 14 – 27 nm. The X-ray diffraction (XRD) analysis informed that the lattice parameter of Ni_1-xCo_xFe₂O₄ nanoparticles at x = 0.3 was 8.423 Å, 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 Ni_1-xCo_xFe₂O₄ nanoparticles also displayed polycrystalline diffraction ring. The fourier transform infrared spectroscopy (FTIR) spectra of Ni_1-xCo_xFe₂O₄ showed the presence of vibration bands of metal ions within the range of 370.33 cm⁻¹ – 601.79 cm⁻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 Ni_1-xCo_xFe₂O₄ nanoparticles at x = 0.2 was 7.0 emu/g, and then increase to 29.0 emu/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 Ni_1-xCo_xFe₂O₄ nanoparticles at x = 0.2 was 59.4 Oe, and then increase to 641.75 Oe at x = 0.6 with increasing Co concentration. This is due to cobalt having higher magnetic anisotropy than nickel.

KEYWORDS:

• Ni_1-xCo_xFe₂O₄
• spinel
• ferrite
• magnetic nanoparticles

Funding

The authors would like to acknowledge Indonesia Endowment Fund for Education (LPDP), Nanofabrication Platform Consortium Project of Nagoya University, Ministry of Culture, Sports, Science and Technologi (MEXT) Nano-Project Platform, Japan and Grant of “Penelitian Berbasis Kompetensi”, Ministry of Research, Technology and Higher Education of the Republic Indonesia (Kementerian Ristek Dikti) for providing financial support for this work.