Synthesis and anomalous magnetic behaviour of NiO nanotubes and nanoparticles

NiO nanotubes and nanoparticles were synthesised via a sol-gel technique followed by heat treatment process. The morphologies of the samples are investigated by transmission electron and field emission scanning electron microscope. X-ray diffraction and selected area electron diffraction patterns imply that the crystal structure of the samples is the cubic polycrystalline. X-ray photoelectron spectroscopy results indicate that the element of Ni is bivalent in the samples. The observation of ferromagnetism at room temperature for the samples has been established with the obvious hysteresis and the coercive field in magnetic hysteresis loops. The zero-field-cooled and field-cooled magnetisation curves prove that there is no contamination of ferromagnetic clusters in the samples. The anomalous magnetic behaviour in antiferromagnetic NiO nanotubes and nanoparticles may arise from the surface spins.