Enhanced Room Temperature Ferromagnetism by Fe Doping 
in Zn0.96Cu0.04O Diluted Magnetic Semiconductors
Zn0.96−xCu0.04FexO (0 ≤ x ≤ 0.04) nanoparticles synthesized via the sol–gel technique had a hexagonal wurtzite ZnO structure without any Fe/Cu-related secondary phases. The crystallite size was reduced from Fe = 0% (23 nm) to Fe = 4% (16 nm) due to the suppression of grain surface growth by foreign impurities. Doping of higher Fe concentrations into Zn-Cu-O suppressed the ultra-violet (UV) emission band and balanced the defect-related visible emissions. The decrease of the UV and green emission intensity ratio (IUV/Igreen) and the UV and blue emission intensity ratio (IUV/Iblue) in photoluminescence spectra implied an increase of defect states with the increase of Fe concentrations. All the samples showed clear room temperature ferromagnetism. The saturation magnetization was increased by Fe co-doping which was attributed to the interaction between Fe-Fe ions. X-ray photoelectron spectra confirmed the absence of secondary phases like Fe3O4.