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

Abstract

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.