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.