Room Temperature Ferromagnetism in $({\hbox {Zn}}_{1-{\rm x}},{\hbox {Mg}}_{\rm x}){\hbox {O}}$ Film

In this work, room temperature ferromagnetism was found in (Zn_1-x, Mg_x)O film with certain Mg compositions (0.06 < x < 0.50). Below the threshold composition (x < 0.06), the film shows no room temperature ferromagnetism (RTFM) and almost no ZnO nanocrystals (NCs) were found in the film. RTF starts to appear in the (Zn_0.94, Mg_0.06)O film, and it becomes maximum in (Zn_1-x, Mg_x)O film with x = 0.20. By detailed analysis of microstructure of the film using high resolution transmission electron microscopy (HRTEM), we found that ZnO NCs were embedded in the ZnO-MgO amorphous phase. Photoluminescence (PL) results show that defects concentrations are quite high in the film. With further increment of Mg composition (x > 0.50), ferromagnetism disappears and the film becomes fully amorphous. Besides, the defects concentration of the film is significantly reduced. The mechanism of RTFM in ZnO-MgO system may be attributed to the interaction ZnO NCs and defects surrounding them.