| Summary: | 碩士 === 國立臺灣大學 === 物理學研究所 === 90 === The Bi films with large ordinary magnetoresistance (OMR) effect have been successfully fabricated by dc magnetron sputtering with adequate post-annealing treatment. In order to obtain the preparation recipe, we have tried three different preparation conditions including post-annealing in the oven, in-situ post-annealing in the chamber and in-situ heating during sputtering.
It has been found that the 3μm Bi film obtained with post-annealing in the oven for 6 hours at 265oC, 6 degree below the melting point of Bi, exhibits a 300% MR ratio in the P-direction under 5 Tesla at room temperature. It can be claimed the largest OMR at room temperature ever found so far.
At low temperatures, it exhibits even larger MR ratio due to the enhancement of the mean free path of Bi. Besides, it shows different field dependence at various temperatures. For example, at 300K, the MR curve is concave. On the contrast, at 2K, it is “S” shape. In the intermediate region, e.g. 77K, it changes from concave to straight and finally becomes convex. It is due to the competition between temperature and field influence. The MR ratio obtained in the T-direction is also found to be smaller than that in the P-direction. It can be ascribed to the finite size effect. Furthermore, at very low temperatures, e.g. 2K, the Bi film exhibit distinct Shubnikov-de Hass (S-dH) oscillations that ensure the quality of this film.
The dominant factors that contribute to the large OMR are discussed in detail in this thesis.
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