High room-temperature magnetization in Co-doped TiO2 nanoparticles promoted by vacuum annealing for different durations

Abstract To clarify the contribution of oxygen vacancies to room-temperature ferromagnetism (RTFM) in cobalt doped TiO 2 (Co-TiO 2 ), and in order to obtain the high level of magnetization suitable for spintronic devices, in this work, Co-TiO 2 nanoparticles are prepared via the sol–gel route, followed by vacuum annealing for different durations, and the influence of vacuum annealing duration on the structure and room-temperature magnetism of the compounds is examined. The results reveal that with an increase in annealing duration, the concentration of oxygen vacancies rises steadily, while the saturation magnetization ( M s ) shows an initial gradual increase, followed by a sharp decline, and even disappearance. The maximum M s is as high as 1.19 emu/g, which is promising with respect to the development of spintronic devices. Further analysis reveals that oxygen vacancies, modulated by annealing duration, play a critical role in tuning room-temperature magnetism. An appropriate concentration of oxygen vacancies is beneficial in terms of promoting RTFM in Co-TiO 2 . However, excessive oxygen vacancies will result in a negative impact on RTFM, due to antiferromagnetic superexchange interactions originating from nearest-neighbor Co 2+ ions.