Synthesis of NiO Nanowires/Nanorods and Their Magnetic Characteristics

摘要

Nanoparticles and nanowiresanorods of NiO have been successfully synthesized by a simple chemical method. The base concentrations of NaOH and calcination temperature have been varied to study their effect on particle size and shape. It has been shown that for a particular molar concentration of 0.02 M and 0.08 M NaOH calcined at 250 ℃, the shape is rod type of nano-dimension. For other molar concentrations of 0.05 M and 0.10 M NaOH and calcination temperatures (of 150 ℃, 250 ℃ and 400 ℃), well shaped and well resolved nanoparticles are observed. X-ray diffraction (XRD) patterns confirmed the formation of crystalline cubic structure of NiO. Transmission electron microscopy (TEM) characterization and the associated selected area electron diffraction (SAED) pattern have revealed poly-crystalline and single-crystalline nature of the rods, with an average aspect ratio of ～10. The magnetic behaviour of the synthesized single-crystalline NiO rods show a ferromagnetic behaviour with a significant coercivity and exchange bias whereas poly-crystalline NiO nanorodsanoparticles show the typical superparamagnetic behaviour of magnetic nanoparticles. The observed magnetic behaviour seems to originate from the uncompensated surface spins and shape anisotropy of the rods.