Effects of hydrogen annealing on room temperature ferromagnetism and optical properties in Zn0.97Cr0.03O nanoparticles

Diluted magnetic semiconductors (DMSs) such as transition metal TM-doped ZnO and TiO₂ are attracting more and more attention due to their promising applications in spintronic devices. Ferromagnetism (FM) in these materials is often associated with ether free carriers or structural defects. Recently, it has been reported that codoping with hydrogen could be an effective way to tune the concentration of mobile carriers or defects and to enhance the FM in ZnO-based DMSs. However, the mechanisms about the effect of hydrogen treatment induced enhancement of FM in TM-doped ZnO system remains unclear. Some authors claim that ferromagnetic metal clusters can be easily reduced with hydrogen treatment and then contribute to the FM, while other authors suggest that the hydrogen can diffuses into the grain interior and causes more defects or defect complex in TM-doped ZnO which result in a larger saturation magnetization.