Annealing Effect to Morphology and Magnetic Properties of Ni Nanoparticles Deposited on the Surface of Al₂0₃Particles

Ni nanoparticles were deposited on Al₂0₃ particles with a diameter of 0.3 μm by the barrel sputterlng technique, and analyzed the prepared samples by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The XRD pattern of the prepared sample did not show any diffraction peak assigned to the Ni metal. On the other hand, both Ni metal and NiO peaks appeared clearly in the XRD pattern of a sample annealed at 873 K for 3 hours. From TEM observations, lt was confirmed that the morphology of Ni deposited on Al₂0₃ particles was not a thin film but nanoparticles with diameters of 2 nm to 20 nm and that the Ni particles partially crystallized. After annealing, Ni particles were aggregated and the average diameter became 24.2 mm. The results of TEM observation were consistent with the results of XRD measurements. The magnetic properties of Ni nanoparticles deposited on Al₂0₃ particles were also examined. The prepared samples showed superparamagnetism, which is one of the characteristic behaviors of magnetic nanoparticles. An exchange-bias effect was also observed, and the effect was reduced by annealing. The magnetic behaviors are explained by the core-Ni shell-NiO structure, which results from the creation of a passivative oxide layer on the Ni nanoparticles in air