Structural, morphological and magnetic studies of cobalt-doped nickel ferrite-MWCNTs nanocomposites

Cobalt-doped nickel ferrites with varying Cobalt ion concentrations (x = 0.0, 0.3, 0.5, 0.7 and 1.0) were synthesized via the chemical co-precipitation method to investigate the effect of cobalt doping on structural and magnetic properties of nickel ferrite. To further enhance the multifunctionality of the material, nanocomposites of Co_0.7Ni_0.3Fe₂O₄ were synthesized with different concentrations (5,10 and 15 %) of multi-walled carbon nanotubes (MWCNTs) using the ultrasonication method. This study aims to understand the combined influence of cobalt doping and CNT incorporation on the material's crystallite size, lattice structure, magnetic behavior, and electronic interactions. X-ray diffraction (XRD) confirmed the formation of a single-phase cubic spinel ferrite, with increasing Co²⁺ content leading to a larger crystallite size. The incorporation of MWCNTs caused a slight shift to higher diffraction angles, indicating a decrease in lattice constant. High-resolution transmission electron microscopy (HRTEM) revealed the spherical morphology of ferrite nanoparticles and the uniform dispersion of MWCNTs. Saturation magnetization was calculated using the Law of Approach to saturation (LAS) method and it increased with cobalt composition up to x = 0.7 (sample Co_0.7Ni_0.3Fe₂O₄), at M_S = 52.90 emu/g and decreased thereafter. Due to the non-magnetic nature of MWCNTs, M_S gradually decreases from 43.55 emu/g for NCM5 to 22.99 emu/g for NCM15. Electron paramagnetic resonance (EPR) spectra demonstrated broadening with increasing cobalt content, while CNT incorporation reduced the resonance field, indicating modified spin interactions. This study highlights the synergistic effects of cobalt doping and MWCNT incorporation in tuning the structural and magnetic properties of nickel ferrite. The findings provide valuable insights for optimizing ferrite–CNT nanocomposites for potential applications in energy storage, sensors, electromagnetic shielding and spintronic devices.