Mapping ferromagnetism in Ti1-x Cox O2: Role of preparation temperature (200-900 °c) and doping concentration (0.000 15≤x≤0.1)

Based on the conflicting reports in the literature, an extensive investigation to map room-temperature ferromagnetic regimes in the Ti1-x Cox O2 system has been undertaken by studying 70 different sol-gel synthesized nanopowder samples by systematically varying x and/or annealing temperatures TA in the 0.000 15≤x≤0.1 and 200-900 °C ranges, respectively. The evolved map demonstrates interesting roles of x and TA resulting in localized regions and pockets of ferromagnetic behavior (≤0.32 μB) which changes gradually to larger nonferromagnetic regions. In general, the ferromagnetic regimes occur at higher Co concentrations as TA increases. X-ray diffraction studies showed a gradual decrease in temperature range at which the anatase-to-rutile transformation occurs in Ti1-x Cox O2 as x increased from 0 to 0.1. Co doping also lowered the band gap energy.