Cobalt-Induced Magnetic Enhancement in Ni/NiO Nanoparticles Embedded in Amorphous Graphene Oxide

Abstract In the present study, pure and cobalt-doped Ni/NiO nanoparticles embedded in amorphous graphene oxide (Co-Ni/NiO@GO) were synthesized using a microwave-assisted sol-gel auto-combustion method, without the direct addition of graphene oxide during the preparation process. Cobalt doping concentrations of 0, 5, 10, 15, 20, and 25% were systematically investigated to understand their influence on the structural, microstructural, and magnetic properties of the nanocomposites. X-ray diffraction analysis confirmed the formation of a face-centered cubic NiO phase with metallic Ni, while the gradual decrease in diffraction peak intensity with increasing Co content indicated reduced crystallite size without altering the crystal structure. Raman spectroscopy revealed the characteristic D and G bands of graphene oxide along with the 1LO vibrational mode associated with Co-doped Ni/NiO. X-ray photoelectron spectroscopy verified the successful substitution of Co ions into the NiO lattice sites. High-resolution transmission electron microscopy demonstrated the formation of well-dispersed Ni/NiO nanoparticles embedded within an amorphous graphene oxide matrix. Magnetic measurements carried out at 4, 150, 220, and 320 K showed that coercivity, saturation magnetization, and remanent magnetization decrease with increasing temperature and increase with higher cobalt doping levels. Notably, the 25% Co-doped Ni/NiO@GOnanocomposites exhibited the highest saturation magnetization of 61 emu/g at 4 K, significantly exceeding that of bulk Ni and NiO. These results highlight the effectiveness of cobalt doping and graphene oxide embedding in tailoring the magnetic performance of NiO-based nanocomposites for advanced applications.