Preparation And Magnetism Of TiO₂/SnO₂ Diluted Magnetic Semiconductors Bulk Samples

In recently years, 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 were introduced into TiO₂/SnO₂by a standard solid-state reaction method and sol-gel method. The magnetization behaviors and the origin of ferromagnetism of Ti_1-xMn_xO₂ samples were studied. The main content of the thesis is as follows:Some of basic properties of DMS and TiO₂, such as lattice structure, magnetic effect,origin of ferromagnetism are also reviewed. To our knowledge, most reports deal with magnetic properties of TE-doped TiO₂ thin film samples rather than bulk samples. Based on a large of studies, we choose the preparation and magnetism of the Mn-doped TiO₂ bulk samples to research.The preparation process and the possible magnetic interactions of the Ti_1-xMn_xO₂ samples had been studied firstly. We find a good preparation method for Ti_1-xMn_xO₂ based on the XRD and magnetization measurement. It is showed that the sintering atmospheres and temperature are important factors to Ti_1-xMn_xO₂ samples. Different sintering atmospheres have remarkably effects on the magnetism properties of Ti_1-xMn_xO₂ samples. The results indicate that the samples sintered in Ar gas show ferromagnetic behavior at room temperatures, but it weaks in samples sintered in air. The Ti_1-xMn_xO₂ samples prepared at low sintering temperature and Mn-doped concentration show ferromagnetic ordering, in contrast, it will weak 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 Ti_1-xMn_xO₂ samples have been experimentally investigated based on the study of the Ti_1-xMn_xO₂ samples. The magnetizations of all the samples show that the Ti_1-xMn_xO₂ 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. By comparing the Ti_1-xMn_xO₂ and Sn_1-xMn_xO₂ samples, in contrast, the magnetization of Mn-doped TiO₂ is higher than Mn-doped SnO₂ at the same concentration.Based on the XRD, it is suggested that all sample's crystal structure is Anatase 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。A possible explanation for the magnetization behaviors of the Ti_1-xMn_xO₂ samples is present according to n-carrier induced-double exchange mechanism. The magnetic ordering of Ti_1-xMn_xO₂ 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 Ti_1-xMn_xO₂ 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 Ti_1-xMn_xO₂ ferromagnetic semiconductors will stimulate the development of spintronics.