Structures And Magnetic Properties Of Ni Doped ZnO- Based Diluted Magnetic Semiconductors

ZnO-based diluted magnetic semiconductors(DMSs) have been extensively investigated in recent years since ZnO has wide band gap and large exciton binding energy. The study on preparation and properties of transition element doped ZnO-based DMSs show great significance to spintronic devices. In this work, ZnO and Ni-doped ZnO samples were synthesized by co-precipitation method. The structures and magnetic properties of Zn1-xNixO powder had been investigated in detail by the X-ray diffraction(XRD), scanning electron microscope(TEM), X-ray photoelectron spectroscopy(XPS) and superconducting quantum interference device(SQUID).This article is divided into three chapters:Firstly,the background of diluted magnetic semiconductors had been briefly reviewed, and the research progress of ZnO-based DMSs were introduced. We also introduced the magnetic research method of DMSs.Secondly, ZnO and Ni-doped ZnO-based DMS powder samples were prepared by co-precipitation method in air atmosphere. The produced samples showed single crystalline wurtzite structure with Ni concentration of less than 5%, the characterizations revealed Ni2+ ions incorporated into the crystal lattice of ZnO. All the samples exhibited ferromagnetic behavior at room temperature(RT). Magnetic moments of samples first decreased and then increased and then decreased, suggested that magnetic property is related not only to the defects ZnO but also to the super paramagnetic exchange interactions between Ni2+, on the other hand the presence of additional anti-ferromagnetic NiO decreased ferromagnetic behavior. The results showed the single crystalline samples were DMSs at room temperature.Finally, the single-phase ZnO-based dilute magnetic semiconductors and heterogeneous ZnO diluted magnetic semiconductors powder samples were prepared by co-precipitation method in nitrogen atmosphere. It found that the saturation magnetization of samples increased with the increasing of doping content of Ni. XRD indicated that the 0-3% Ni-doped samples were single crystalline wurtzite structure while above 3% Ni-doped ZnO samples the Ni phases were found. The saturation magnetization were obtained to be 0.28 emu/g for ZnO0.97Ni0.03 O sample. Then, it can be speculated that the ferromagnetism mainly comes from the deposition of magnetic Ni and the oxygen vacancies of ZnO. Compared with these two results, we speculated that preparation conditions play an important role in the Ni-doped ZnO.