A study on magnetic, electrical properties and magnetoresistance effect of La1-X AMnO3-delta (A=vacancy , Sr) system
| Autor: | Guo-Ju Chen, 陳國駒 |
|---|---|
| Rok vydání: | 2000 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 89 The microstructure evolutions of polycrystalline La1-xAxMnO3- (A= vacancies and Sr; x=0 ~ 0.5) films during calcined processes for MOD and RF sputtering methods were studied. The effects of the substitution by vacancies and/or Sr ions at La sites on the magnetic and electrical properties of the La1-xAxMnO3- (A= vacancies and Sr; x=0 ~ 0.5) films were discussed. The experimental parametric dependence of magnetoresistance of films was also investigated. From the experimental results, the secondary phase of Mn3O4 shows in the films and the bulk samples while La deficiency higher than 0.2. By high-resolution transmission electron microscopy observations, the irradiation damages were found due to the introduction of vacancies. An insulator-metal transition was observed for all La1-xMnO3- films. At room temperature, the MR ratio of the x = 0.3 film was 8.4 % at the field up to 1.67T. The phase of LaSrMnO3 film is strongly affected by the substitution of Sr ions. By proper replacement of Sr ions, the average radius could be adjusted to be 1.23, and the magnetic transition temperature was elevated to 337K. Because of the magnetic transition temperature markedly exceeded well above room temperature, the magnetic spins aligned in parallel. It extends the application of the magnetoresistive LaSrMnO3 films at room temperature. As for the La0.7MnO3 films prepared by RF magnetron sputtering, the microstructure strongly depended on the buffer system. Stresses arising during post annealing were relaxed by forming defect structures in the films. The best magnetoresistive performance of about 30 %MR (measured at 150K and in an applied field of 1.67 T ) was obtained in the La0.7MnO3/YSZ/Si films grown at 450℃. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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