Mapping ferromagnetism in Ti_(1-x)Co_xO_2: Role of preparation temperature (200-900 deg C) and doping concentration (0.00015<= x<= 0.1)

摘要

Based on the conflicting reports in the literature, an extensive investigation to map room-temperature ferromagnetic regimes in the Ti_(1-x)Co_xO_2 system has been undertaken by studying 70 different sol-gel synthesized nanopowder samples by systematically varying x and/or annealing temperatures T_A in the 0.000 15<=x<=0.1, and 200-900 deg C ranges, respectively. The evolved map demonstrates interesting roles of x and T_A resulting in localized regions and pockets of ferromagnetic behavior (<=0.32 mu_B) which changes gradually to larger nonferromagnetic regions. In general, the ferromagnetic regimes occur at higher Co concentrations as T_A increases. X-ray diffraction studies showed a gradual decrease in temperature range at which the anatase-to-rutile transformation occurs in Ti_(1-x)Co_xO_2 as x increased from 0 to 0.1. Co doping also lowered the band gap energy.