Nickel nanoparticles in silica glass fabricated by 60 keV negative-ion implantation

摘要

Magnetic nanoparticles are fabricated in silica glass (SiO_2) using high-flux implantation of 60 keV negative nickel ions Ni~-. Photo-absorption measurements and cross-sectional transmission electron microscopy (XTEM) observation confirm the formation of metallic Ni nanoparticles in SiO_2, and exclude the possible formation of Ni silicides (Ni_3Si, Ni_2Si, NiSi) and oxides (NiO) as major products. The mean diameter of the nanoparticles was ～2.9 nm, and the observed depth distribution was similar to a prediction from the TRIDYN code when sputtering was accounted for. Temperature- and field-dependences of magnetization show that the nanoparticles are in the superparamagnetic state at T >～ 50 K. From the peak temperature of the zero-field cooling (ZFC) magnetization, which is ～27 K, and the mean diameter determined from XTEM, it is suggested that the magnetic anisotropy constant K of the nanoparticles is enhanced by ～8 times as compared to the bulk value.