Synthesis of Ni/NiO nanocomposites by hydrothermal-assisted polyol process and their magnetic properties as a function of annealing temperature

• Published in: Powder technology Vol. 274; pp. 98 - 104
• Main Authors: Gokul, B., Saravanan, P., Vinod, V.T.P., Černík, Miroslav, Sathyamoorthy, R.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.04.2015
• Subjects: Exchange bias; Glycerol; Hydrothermal; Ni/NiO nanocomposites; Polyol process; Ni/NiO nanocomposites; Glycerol; Polyol process; Hydrothermal; Exchange bias
• ISSN: 0032-5910; 1873-328X
• DOI: 10.1016/j.powtec.2015.01.002

In this study, the composition, morphology and magnetic properties of Ni/NiO nanocomposites synthesized by hydrothermal-assisted polyol process were studied as a function of annealing temperature. Upon increasing the annealing temperature from 300 to 500°C, the concentration of NiO was found to increase at the expense of metallic Ni-core and a complete transformation of NiO was evidenced at 500°C. All the Ni/NiO nanocomposites demonstrated strong exchange bias (EB); however, the mechanism of the EB effect seems to be different in each case. For the samples annealed at low temperatures: 300 and 400°C, the EB effect arises from the coupling at the Ni/NiO interface; whereas for the samples annealed above 400°C, the EB effect is due to the coupling between frozen magnetic moments of NiO-shell and typical antiferromagnetic NiO-core. Enhancement in the EB and large coercivity were obtained for the sample annealed at 500°C. Through this study, it has been demonstrated that the EB effect in the Ni/NiO nanocomposites can be tuned by controlling the composition and particle size of both ferromagnetic (Ni) and antiferromagnetic (NiO) components. [Display omitted] •Ni-NiO nanocomposites are synthesized by hydrothermal-polyol process.•Glycerol is used as a polyol, which serves as both a reducing and a stabilizing agent.•Large enhancement in exchange bias coupling and coercivity is achieved.•Disordered frozen moments on the surface are responsible for exchange bias effect.