Enhanced room-temperature ferromagnetism in un-doped ZnO thin films by thermal annealing in a strong magnetic field

Abstract

Room-temperature ferromagnetism was achieved in un-doped ZnO films by annealing the films in flowing argon at 650 °C. The ferromagnetic property of the ZnO films can be manipulated by applying an external magnetic field during annealing, with a maximum of 2.7 emu/g achieved at a field of 7 T, which is almost double that when no magnetic field was applied. The reason is that the magnetic field influenced greatly the involvement of oxygen defects which are origin of the ferromagnetism of these un-doped ZnO films.