Novel magnetic generation of ultrathin Co/ZnO (002) surface by post low-energy N+ sputtering

A novel magnetic generation of ultrathin film was discovered by the surface magneto-optical Faraday effect (SMOFE) in ultrahigh vacuum (UHV). The use of SMOFE measuring system is due to the natural color of the ZnO(002) substrate was light yellow and transparent. In this presented article, we are going to show how to accomplish the experiment in the first paragraph and to obtain the magnetic property of the sample. First, a clean (10 × 10 × 0.5 mm³) ZnO (002) crystal surface was bombarded by Ar⁺ plasma. Second, the Co ultrathin film was epitaxially grown on the substrate. The magneto-optical signals of the Co/ZnO film can distinguish the thickness between ultrathin and thick range from the observation of typical hysteresis loops. At a very thin thickness range approximate to atomic layer (~ 0.2 nm), we can not observe any magnetic signal. Further, was interestingly, the ZnO sample with Co coated film then appears magneto-optical intensities by a low-energy nitrogen plasma sputtering for several minutes. We checked the N/Co/ZnO composition near the surface regime by Auger electron spectroscopy (AES). It is a strong evidence to explain the result related to the generation of the ferromagnetism.