Annealing effects on structure and magnetic properties of Mn-doped TiO2

• Ti1−xMnxO2 nanopowders (x=0.02) were prepared by solid state method.
• Ti1−xMnxO2 nanopowders annealed at different annealing temperatures (TA).
• All samples exhibited room temperature ferromagnetism (RTFM).
• Average magnetic moment per Mn atom decreased with increasing TA.
• The FM was interpreted by the BMP model, in which both VO and Mn ions are involved.

Ti1−xMnxO2 powder samples with nominal manganese concentration x=0.02 were synthesized by a solid state reaction route. Thermal treatment of the samples was carried out in air at temperatures of 500, 600 and 700 °C. The samples were investigated by x-ray diffraction, photoluminescence and magnetization measurements. Photoluminescence studies indicated presence of oxygen vacancy defects in TiO2 lattice. Room temperature M–H loops showed a ferromagnetic behavior for all Ti1−xMnxO2 samples, and the magnetization of samples decreases with increasing annealing temperature. Temperature-dependent magnetization measurements showed evidence for ordering temperature of >420 K. However, the experimental results indicate that the ferromagnetism observed in Ti1−xMnxO2 samples is intrinsic rather than associated with secondary phases. It seems that the ferromagnetic phase could originate from interactions between manganese ions and oxygen vacancies and/or defects incorporated in the TiO2 crystal lattice during the thermal treatment of the samples.