Surface ferromagnetism in ZnO single crystal

Abstract

We report on the room temperature surface ferromagnetism in undoped ZnO bulk single crystal. Typical ferromagnetic saturation behavior is clearly demonstrated by magnetization loops, and the saturated magnetization can be manipulated by annealing under argon atmosphere. A strongly correlation, between the saturated magnetization and the concentration of singly occupied oxygen vacancies on the surface of ZnO single crystal, is established by means of the Raman spectra, photoluminescence, electron paramagnetic resonance and atomic force microscope. It is suggested that the observed room temperature ferromagnetism in ZnO single crystal should be attributed to the effect of surface oxygen vacancy defects. This finding may help to get further insight into the ferromagnetic origin in other undoped oxide semiconductor materials.