Preparation And Magnetism Of Zn_1-xTE_xO (TE=Mn,Co,Cu) Diluted Magnetic Semiconductors Bulk Samples

Diluted magnetic semiconductors (DMS),which integrate the magnetism and semiconducting properties, are very significant from the view of both basic research and device application. So far, research on diluted magnetic semiconductor is one of the hot topics in the world. In this thesis, magnetic transition metallic elements(TE=Mn, Co,Cu ) were introduced into ZnO by a standard solid-state reaction method, the magnetization behaviors and the origin of ferromagnetism of Zn1-xTExO samples were studied. The main content of the thesis is as follows: The study background and application perspectives of DMS are introduced. Some of basic properties of DMS and ZnO, such as lattice structure, magnetic effect,origin of ferromagnetism are also reviewed. To our knowledge, few reports deal with magnetic properties of TE-doped ZnO bulk samples. Based on a large of studies, we choose the preparation and magnetism of the TE-doped ZnO bulk samples to research. The preparation process and the possible magnetic interactions of the Zn1-xMnxO samples had been studied firstly. We find a good preparation method for Zn1-xMnxO based on the XRD and magnetization measurement. It is showed that the sintering atmospheres and temperature are important factors to Zn1-xMnxO samples. Different sintering atmospheres have remarkably effects on the magnetism properties of Zn1-xMnxO samples. The results indicate that the samples sintered in Ar gas show ferromagnetic behavior at room temperatures, but it disappears in samples sintered in air. The Zn1-xMnxO samples prepared at low sintering temperature and Mn-doped concentration show ferromagnetic ordering, in contrast, it will disappear at high sintering temperature and Mn-doped concentration. All the samples'magnetization is much smaller than theoretic value, it suggests that there are competitions of antiferromagnetic and ferromagnetic interactions between Mn ions. The structure and magnetization behaviors of Zn1-xCoxO samples have been experimentally investigated based on the study of the Zn1-xMnxO samples. The magnetizations of all the samples show that the Zn1-xCoxO samples prepared at low sintering temperature and Co doped concentration show ferromagnetic ordering, in contrast, it will disappear at high sintering temperature and Co doped concentration. By comparing the Zn1-xMnxO and Zn1-xCoxO samples, it is showed that the solubility of Mn-doped ZnO is lower than Co-doped ZnO, in contrast, the magnetization of Mn-doped ZnO is higher than Co-doped ZnO at the same concentration because that Mn2+ has five d-electrons and Co2+ has three d-electrons. Additional impurity Cu and Mn are co-doped into Zn1-xMnxO and Zn1-xCoxO samples respectively, and their magnetic properties have been investigated based on the study of the Zn1-xMnxO and Zn1-xCoxO samples. By comparing the Mn-doped ZnO and (Mn,Cu)-codoped ZnO samples, it is found that the additional p-type element Cu co-doped into Zn1-xMnxO is not good to add ferromagnetic ordering, in contrast, it decreases the magnetization of the Zn1-xMnxO samples; at the same time, the additional n-type element Mn co-doped into Zn1-xCoxO is good to add the sample's ferromagnetic ordering. Based on the XRD, it is suggested that all sample's crystal structure is Wurtzite under low doped concentration, and the secondary phase is not found under the sensitivity of our apparatus. Based on the structure analysis, magnetization measurement and preparation process, it is suggested the magnetism of the samples comes from itself intrinsically, not from the secondary phase。It is contradictory about the origin of the sample's magnetism, based on our studies, a possible explanation for the magnetization behaviors of the Zn1-xTExO samples is present according to n-carrier induced-double exchange mechanism. The magnetic ordering of Zn1-xTExO samples would not appear if there are not n-type carriers in samples. So far, it is reported that many DMS film samples not only Curie temperature are low,but also its reproducibility is not high. In contrast, the standard solid-state reaction is a good method for preparing diluted magnetic semiconductor, the Zn1-xTExO samples which we prepare have room-temperature ferromagnetic ordering and good reproducibility. Diluted magnetic semiconductors could be used to construct magnetic and electronic device that utilize simultaneously the spin and charge degrees of freedom of carrier. So, recent research on Zn1-xTExO ferromagnetic semiconductors will stimulate the development of spintronics.