Room temperature ferromagnetism in Ni, Fe and Ag co-doped Cu–ZnO nanoparticles: an experimental and first-principles DFT study

We report an experimental and theoretical investigation on the room temperature ferromagnetism of Zn_0.95Cu_0.05O and Zn_0.94Cu_0.05M_0.01O (M=Ni, Fe and Ag)Ni nanoparticles synthesized by sol–gel method. X-ray diffraction analysis reveals single hexagonal wurtzite; meanwhile the lattice parameters are found to be sensitive to the ionic radius of the doping elements and the crystallite size varies in the range 22–47 nm. Field emission scanning electron microscopy observations show particles with spherical shape for ZnO and semi-spherical shape for co-doped nanopowders. Magnetic measurements using SQUID reveal room temperature ferromagnetic ordering for doped and co-doped nanopowders with a lower saturation magnetization compared to Cu-doped ZnO. It is found that the co-doping has resulted in weakening the ferromagnetic phase at the expense of the paramagnetic. First-principles calculations indicate that only Cu and Fe codoped ZnO systems own ferromagnetism, which originated from the interaction between Fe-d and O-p electrons. However, all doped systems show positive formation energies indicating they are less stable than undoped ZnO.