Influence of cooling field on the magnetic properties of Ni/NiO nanostructure

Nanoparticles of Ni/NiO structure were prepared by sol–gel route followed by the annealing in presence of controlled oxygen and argon gas mixture. When the sample was cooled down to 5 K from room temperature in a static magnetic field, a systematic shift of the magnetic hysteresis loop was observed. The shift was absent when the sample was cooled in zero field. For cooling the sample in field-cooled mode a small horizontal shift was noticed along with a moderate vertical shift of the hysteresis loop at the saturation of magnetization, which indicates the typical manifestation of exchange bias effect. The horizontal shift increases with decreasing particle size retaining almost unchanged relative vertical shift, where vertical shift is found to be uncorrelated with the horizontal shift. The exchange bias like effect in the Ni/NiO nanostructure is suggested at the Ni/NiO interface, where Ni is ferromagnetic and NiO is in the disordered magnetic state.