Preparation, Microstructure, Ferroelectricity And Ferromgnetism Properties Of (Me, Li) Co-doped ZnO Films

We have studied the ferroelectricity and ferromagnetism properties of TM and Li co-doped ZnO films deposited by implantation and reactive magnetron sputtering. The multiferroic property was found in ZnO:CoLi and ZnO:CuLi films and the ferromagnetism mechanism was studied. Additionally, we found room temperature ferromagnetism and p-type doping in Mn and Li co-doped ZnO films which have great contribution for the application in photoelectric device.Simultaneous room temperature ferroelectricity and magnetism was observed in (Co, Li) co-implanted ZnO films. The implantation were conducted for Li and Co at energies of 50 and 400 keV, respectively, to doses of 1×1016cm-2 and 5×1016 cm-2. Remnant dipole polarization of 10.2μC/cm2 and coercive electric field of 24.8 kV/cm were recorded for co-implanted ZnO films annealed at 700℃. The implanted samples annealed at 700℃also exhibited a saturation magnetization over 11.4×10-5 emu and coercive magnetic field of 67 Oe. The ferroelectricity is interpreted by the ionic radius difference between the dopants and host cations, and the magnetism is explained by bound magnetic polarons mediated by electrons and defects.Single-phase Zn0.95-xCuxLi0.05O thin films have been prepared on Pt (111)/Ti/SiO2 substrates by reactive magnetron sputtering method. The XRD, XPS and absorption measurements confirmed the polycrystalline nature of the films and the substitution of Zn2+ by Cu2+ ions. The sputtered Zn0.90Cu0.05Li0.05O film shows multiferroic properties exhibiting a saturated ferroelectric loop with a remanent polarization of 6μc/cm2 and a saturated loop with a saturation magnetization of 0.43μB/Cu at room temperature. The origins of the ferromagnetism and ferroelectricity in these films are discussed.We report on defects related room temperature ferromagnetic characteristics of Zn0.95-xMnxLi0.05O (x=0.01,0.03,0.05 and 0.08) thin films grown on glass substrates using reactive magnetron sputtering. By increasing the Mn content, the films exhibited increases in the c-axis lattice constant and fundamental band gap energy, coercive field and remanent magnetization. Comparison of the structural and magnetic properties of the as-deposited and annealed films indicates that the holes carriers, together with defects concentrations, play an important role in the ferromagnetic origin of ZnMnO. The ferromagnetism in films can be described by bound magnetic polaron models with respect to defect-bound carriers.Multiferroic materials have great application in spintronics and photoelectric devices. We preliminarily study the multiferroic propreties of ZnO films by co-doping methods, and find room temperature ferromagnetism and ferroelectricity in Me and Li co-doped ZnO film. By co-doping with RE (rare earth) elements, such as Gd and Er, we hope to doposit ZnO films with superior coercive magnetic field and saturation magnetization.