Large magnetoresistance in carbon coated Ni/NiO nanoparticles

Subir Roy, Rajesh Katoch and S. Angappane
Bull. Mater. Sci. 41, 127 (2018); DOI: 10.1007/s12034-018-1645-8

(a) MR of C-Ni/NiO nanocompacts at 300 and 18 K. (b) Low temperature MR and MH loop of C-Ni/NiO nanocompact.

We report here a large magnetoresistance (MR) observed in carbon coated Ni/NiO nanostructures synthesized by a chemical method. The crystalline nature and particle size of the graphitic carbon coated Ni/NiO nanostructure was investigated by X-ray diffraction study and field emission scanning electron microscope (FESEM) images. The Raman spectroscopy confirms the presence of graphite layer over the Ni/NiO nanostructure. The field cooled magnetic hysteresis curves show exchange bias effect suggesting possible Ni/NiO core-shell structure. The temperature dependent magnetization data shows bifurcation in field cooled (FC) – zero field cooled (ZFC) curves indicating the superparamagnetic behavior and competing ferromagnetic and anti-ferromagnetic interactions in the nanocomposite. Magnetoresistance studies show a large negative MR of ~ 20% at 18 K and ~ 4.2% at room temperature, revealing significant enhancement of ferromagnetic interactions at low temperatures and spin dependent tunneling of current through the nanocomposite.