Influence of thermal treatment on tuning the ferromagnetism in Mn-doped ZnO film

•Thermal treatment could increase effective doping density of Mn2+ ions in Mn-doped ZnO.•Largest magnetism is in the700 °C N2-annealed film subsequently annealed at 630 °C in H2.•The different annealing temperature and atmosphere could tuning the ferromagnetism.•Higher pre-annealed temperature (>700 °C) caused the formation of ZnMn2O4 precipitates.

The effect of thermal treatment on the structural, optical, and magnetic properties of Mn-doped ZnO film prepared by radio frequency magnetron sputtering has been investigated. Higher pre-annealing temperature (>700 °C) in O2 or N2 caused the formation of a ZnMn2O4 room-temperature paramagnetic precipitate which decreased the amount of substituted Mn2+ ions in ZnO matrix. Meanwhile, the amount of oxygen vacancies, especially the singly ionized oxygen vacancies, increased after N2/H2 annealing obtained by the analysis of photoluminescence spectrum. So based on the bound magnetic polaron model, we emphasized that the effective doping density of Mn2+ ions together with the singly ionized oxygen vacancies play an important role in tuning the magnetic coupling of Mn-doped ZnO film.