Preparation of Ni Nanoparticles on Submicron-Sized Al2O3 Powdery Substrate by Polyhedral-Barrel-Sputtering Technique and Their Magnetic Properties

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Ni nanoparticles were prepared on a submicron-sized Al2O3 powdery substrate by the polyhedral-barrel-sputtering technique and their microstructure and magnetic properties were investigated. By this technique, nanoparticles with an average diameter of 3.9--7.9 nm were prepared on the Al2O3 particles surface, and the size distribution of the nanoparticles was reproduced using a log-normal formula. The deposited Ni nanoparticles were composed of a NiO layer, which was formed by air oxidation, and a Ni core. The magnetization curves suggested that the all the prepared samples exhibited superparamagnetic behavior, which can be explained by considering the size distribution of the Ni nanoparticles. An exchange-bias effect, which arising from the core--shell structure, was also observed. From the saturated magnetic moments of the Ni core, the thickness of the surface layer was estimated to be 1.0--1.3 nm, which was comparable with that of passivated oxide layer of bulk Ni.
2012-06-25