Magnetic behavior of Ni+ implanted silica

Ni+ has been implanted in amorphous silica layers and silica glasses at two dose levels (10(16) and 10(17) Ni+ cm(-2)) and two different energies (30 and 160 keV). Superparamagnetic and ferromagnetic behaviors were observed w ith a SQUID magnetometer at RT and 5 K, respectively. Using Langevin's theo ry, the size of the metallic nanoparticles were deduced to ranges between 2 and 6.5 nm in good agreement of HRTEM observations. The E' type center and the neutral oxygen vacancy (NOV) defects were observed by UV-Vis absorptio n. Finally, in samples annealed at 600 degrees C under Ar or Ar+H-2 atmosph eres two different phenomena were observed: the reduction of Ni2+ to Ni-0 a nd the elimination of defects introduced by implantation. (C) 1999 Elsevier Science B.V. All rights reserved.