  We report on structural, magnetic and electronic properties of Co-implanted
TiO2 rutile single crystals for different implantation doses. Strong
ferromagnetism at room temperature and above is observed in TiO2 rutile plates
after cobalt ion implantation, with magnetic parameters depending on the cobalt
implantation dose. While the structural data indicate the presence of metallic
cobalt clusters, the multiplet structure of the Co L3 edge in the XAS spectra
gives clear evidence for a substitutional Co 2+ state. The detailed analysis of
the structural and magnetic properties indicates that there are two magnetic
phases in Co-implanted TiO2 plates. One is a ferromagnetic phase due to the
formation of long range ferromagnetic ordering between implanted magnetic
cobalt ions in the rutile phase, and the second one is a superparamagnetic
phase originates from the formation of metallic cobalt clusters in the
implanted region. Using x-ray resonant magnetic scattering, the element
specific magnetization of cobalt, oxygen and titanium in Co-implanted TiO2
single crystals are investigated. Magnetic dichroism was observed at the Co L
edges as well as at the O K edge. The interaction mechanism, which leads to
ferromagnetic ordering of substituted cobalt ions in the host matrix, is also
discussed.
