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

Abstract

Abstract To clarify the contribution of oxygen vacancies to room-temperature ferromagnetism (RTFM) in cobalt doped TiO2 (Co-TiO2), and in order to obtain the high level of magnetization suitable for spintronic devices, in this work, Co-TiO2 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-TiO2. However, excessive oxygen vacancies will result in a negative impact on RTFM, due to antiferromagnetic superexchange interactions originating from nearest-neighbor Co2+ ions.