Morphology-controlled synthesis of monodispersed graphitic carbon coated core/shell structured Ni/NiO nanoparticles with enhanced magnetoresistance.

Graphitic carbon coated core/shell structured Ni/NiO nanoparticles were synthesized by a sol-gel type chemical precursor method and their structural, morphological and magnetic properties were evaluated. The synthesis method provides an improved and comparatively facile approach towards controlled growth of the composite structure of a metallic ferromagnetic (FM) core and an antiferromagnetic (AFM) metal oxide shell along with in situ growth of a supplementary surface functionalization layer of graphitic carbon. In addition, the process allows a precise control over the shape and size of this important class of core/shell type functional materials for a wide range of pertinent applications. The structural properties of the derived samples were studied with X-ray diffraction (XRD), X-ray absorption near edge structure (XANES), extended X-ray absorption fine structure (EXAFS), Raman spectroscopy, energy dispersive X-ray (EDX) analysis, and X-ray photoelectron spectroscopy (XPS). The microstructural features in the core/shell structured particles were evaluated using a scanning electron microscope (SEM) and a high resolution transmission electron microscope (HRTEM). Magnetic properties of the derived samples were studied using a vibrating sample magnetometer (VSM) in the 80-300 K temperature range. The surface functionalized Ni/NiO nanoparticles exhibit a distinctly enhanced magnetoresistance (MR), e.g., -10% at 290 K, than reported values in compacted Ni/NiO powders or composites.