Ion implantation technique was used to study the magnetic property in Co-doped ZnO and Cu-doped ZnO.  The Co ions energy of implantation was 80keV with the fluence ranging from 1×10¹⁴ions.cm^-2 to 1×10¹⁷ions.cm^-2. The Cu ions were implanted at an energy of 70keV with the fluence of 5×10¹⁶ions.cm^-2. These samples were analyzed by means of X-ray diffraction (XRD), photoluminescence(PL), X-ray photoelectron spectroscopy(XPS) and Vibrating sample magnetometer (VSM). XPS and PL analysis indicated that Co²⁺ ions substituted for Zn²⁺ ions without changing ZnO wurtzite structure. VSM measurement shows that all implanted samples is ferromagnetism and the saturation magnetization is from 6.89×10^-5 to 2.31×10^-4 emu before and after annealing. The saturation magnetization increases with increasing implantation fluence between 5×10¹⁴ions.cm^-2 to 1×10¹⁶ions.cm^-2, but it decreases with the increasing implantation fluence between 1×10¹⁶ions.cm^-2 to 1×10¹⁷ions.cm^-2. It means the fluence of implantation can impact the magnetic properties of the implanted samples. Considering the Co-metal nanocrystals were detected from X-ray diffraction in this work, and metal Co is ferromagnetic with Tc=1373K, we hold that the observed ferromagnetism is consistent with these Co nanocrystals. But we are skeptical whether ferromagnetic ordering only arises from the secondary magnetic phases or metal precipitates. So we have prepared the Cu-doped ZnO samples. The room temperature ferromagnetism in the Cu-implanted ZnO samples has been observed. We argue that the ferromagnetism is related to the presence of Co nanocrystals, and the substitution of Co²⁺ into Zn²⁺ sites in crystal ZnO could contribute to the observed ferromagnetism.

Correspondence should be addressed to Li Gong-Ping (email: ligp@lzu.edu.cn)

This work was supported by the Open Project of Key Laboratory for Magnetism and Magnetic Materials of the Ministry of Education, Lanzhou University, the SRF for ROCS, SEM and Chun Hui Project of Ministry of Education.