Structure and magnetic properties of Co+-implanted silica

Cobalt has been implanted at 30 and 160 keV in three different silica-based substrates. TEM observations and magnetization measurements performed at RT and 5 K show that, after implantation, cobalt is present both as metal particles, few nanometers in size and as smaller oxide particles. Optical absorption measurements show that the presence of oxide particles is linked to the formation of Si-Si bonds during implantation. After thermal treatment under hydrogen, cobalt is entirely in the metallic form and saturation magnetization becomes close to its theoretical value. Last, the initial amount of oxide depends on the OH content of the substrate. (C) 2001 Elsevier Science B.V. All rights reserved.