Systhsis And Properties Of ZnO Diluted Magnetic Semiconductor

Diluted magnetic semiconductors (DMSs) have initiated a great deal of interests in recent years because their unique manipulation of both the electron charge and spin freedom can be realized in these materials. They have been considered as very promising candidates for spintronic devices. After the theoretical prediction suggested by Dietl et al. the existence of room temperature ferromagnetism in Mn doped GaN and ZnO, transition metal (TM) doped GaN has been systemicly studied and the good results have been obtained. At the same time, ZnO system has been extensively studied. Remarkable progress has been made in the realization of TM-doped ZnO with Curie temperature at or above room temperature. However, the mechanism of intrinsic ferromagnetism in TM-doped oxides is still under debate. A diversity of theories has been proposed. As a direct wide band gap semiconductor, ZnO is widely used in many fileds due to its photoelectricity,piezoelectricity and gas-sensitivity. Therefore, the research on the origin of the ferromagnetism in ZnO DMS is valuable on theory and application.Recently, the origin of the ferromagnetic of ZnO DMS is widely considered to be related toTM dopants,defects and magnetic impurities. In this work, we adjusted TM dopant concentrations to investigate the effect of TM dopants on the origin of the ferromagnetism, adjusted the defects based on the annealing process to study the effect of the defects on the ferromagnetism. There is no effective method and tool to detect the magnetic impuries in the ZnO DMS. So, several metals with different magnetic properties were employed to be dopped into ZnO to investigate the effect of the magnetic impuries on the origin of the ferromagnetism.Mn,Ni,Cu doped and undoped ZnO nanoparticles were prepared in a simple solution route and parts of them were annealed in some different atmospheres. The structures of the prepared particles are in single hexagonal wurtzite phase, and there is no indication of extra TM-related second phases in the prepared nanorods with the low dopping contents. The dopants are in the +2 valence oxidation state and are uniformly distributed in the nanoparticles. Magnetization loops of the samples were measured and clearly show that the typical ferromagnetic saturation behavior.There are three peaks at visible band in the RT photoluminescence spectra, 527nm,575nm and 657nm, related to the singly ionized oxygen vacancies (Vo+), the doubly ionized oxygen vacancies(Vo++) and the intrinsic defects of oxygen interstitials (Oi), respectively. From the Photoluminescence and magnetism measurements, a clear positive correlation between the saturated magnetic moment and the intensity of Vo+ is observed. The adjustment of magnetism by the concentration of the defects are more effective that by the concentration of ion dopants.We theoretically studied the possible magnetic defect centers in the 1.5%Mn,1%Ni,1%Cu doped ZnO and undooed ZnO by first-principles calculations. The calculated local magnetic moment of various defect centers including a single oxygen vacancy (Vo) in 2-,1-, and neutral charge states, Zn vacancies and oxygen interstitials (Oi) and the complexes of these oxygen vacancies bound with one or two substitutional TM dopants. For the single oxygen vacancies, only the one of 1-charge state poses the magnetic moment of about 1 uB, and for the Vo-TM complexes, the results are different with the several TM ions.With the Combination of the defects analyses based on Photoluminescence spectra and magnetism results, we found the origin of the ferromagnetism is mostly related to the Vo+ defects. For the TM doped ZnO systems, the observed RT ferromagnetism can be explained by the direct effect of the Vo+ defects or the effect of the defects along with the ferromagnetic coupling among the TM dopants mediated by them. While in the pure ZnO, it is obviously the the Vo+ is response for the RT ferromagnetism.In the study of a number of TM-doped and undoped ZnO-based DMS, some different explaintions are found on the orgion of the ferromagnetism. In any sense, the present theoretic and experimental results show clearly that the Vo+ defect plays a concluded role in tuning the ferro-magnetism of the TM doped and undoped ZnO.