Structure and Magnetism of Co-implanted TiO₂

Crystalline Co nanocomposites in the rutile TiO₂ were synthesized by 180 keV Co ion beam implantation at temperature of 623 K with the fluence of 4×10¹⁶ cm^-2. The structural and magnetic properties of samples with different thermal treatment were characterized by synchrotron radiation X-ray diffraction (SR-XRD), high resolution transmission electron mi-croscopy (HRTEM), Rutherford backscattering/channeling and the superconducting quan-tum interference device magnetometer. The SR-XRD results reveal the formation of hcp and fcc phases of Co clusters, and the SR-XRD and HRTEM show that Co nanocrystals (NCs) have been formed in TiO₂ after ion implantation. With increasing of annealing tem-perature, the transition of hcp to fcc Co is observed, and the Co NCs sizes were increased with increasing post-annealing temperature. At annealing temperature 1073 K, the lattice damaged is significantly removed compared with the virgin sample. The Co NCs forming inside TiO₂ are the major contribution of the measured ferromagnetism.