| History has proved over and over again, the development level of material science is an important symbol of human civilization advancement extent. The come out of new material with special property often lends to the great breakthrough of technology, even brings out a revolution in technology. The discovery of Ge transistor in Bell library in 1947, and the naissance of the first commercial transistor after five years, leading to the flourish development of microelectronics and the advent of the contemporary information, can be the greatest embodiment of this. The pioneer application of colossal magnetoresistance effect in the field of sensor, slide and memorizer and the attracted application foreground which showed in the field of spin transistor,entirely metallic computer and quanta-computer are the newest examples from the development of science to the fast transition of commercial application.In the investigative background of the colossal magnetoresistance material, this paper selects optimal hole-doping manganites as the mother material for our study, and uses different methods to compound it with high resistance oxides. The transport properties under zero and applied field of the compound samples are studied. The dissertation consists of six chapters:In chapter one, we made a summary of the crystal and electronic structure, the CMR effect of the manganese perovskites and the related mechanism. The works which have been done for the sake of enhancing the low field magnetoresisitance have been given. On the basis of this, we put forward the content and orientation of this thesis.In chapter two, the preparation techniques of the manganese perovskites have been introduced. Solid state reaction, which is the most convenient and easy method, is selected to prepare the composites. And the structure, micrograph and the electronic and magnetic transportation properties have been studied in La0.7Ca0.2Sr0.1MnO3. The preparation methods of nano-ZnO have also been presented.In chapter three, the La0.7Ca0.2Sr0.1MnO3/ZnO composites have been prepared by solid state reaction. The structure,micrograph and the electronic and magnetic properties of the composites have been particularly studied. And the mechanisms in the arisen phenomenon have been specially discussed. The results show that, ZnO segregated at the grain boundaries and the surfaces of the LCSMO grains and caused magnetic disorder. With the doping level of ZnO increase, the maximum magnetoresistance appeared from low temperature to high temperature (near room temperature).In chapter four, the La0.7Ca0.2Sr0.1MnO3/ZnO composites have been prepared through liquid phase method. The structure and electronic and magnetic properties of the composites have been investigated in contrast to the results via solid state reaction. There were great differences in electro-magnetic properties between the results of two methods.In chapter five, the La0.7Ca0.2Sr0.1MnO3/ZnFe2O4 composites have been prepared through the method of solid state reaction. The researches on the structure, electronic and magnetic properties have been done. It has been observed that the incorporation of ZnFe2O4 phase into LCSMO matrix lowers the metal-insulator transition temperature and the ferromagnetic order of LCSMO is weakened by addition of ZnFe2O4. With the increasing content of ZnFe2O4, the maximum room temperature magnetoresisitance appeared when the low temperature magnetoresisitance reaches to the maximum.Summarizations are concluded in chapter six. |
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