摘要

本計劃之主要目的是希望提昇L1-xAxMnO3(A=Ca、Sr、Ba)在低磁場下的磁阻效應，材料以La0.7Sr0.3MnO3與La0.7Ca0.3MnO3為主軸，此二材料均在居禮溫度上下有順磁性－鐵磁性之磁性轉換，其中La0.7Sr0.3MnO3之轉換溫度約360K，較有應用之可能性，La0.7Ca0.3MnO3之轉換溫度則約250K。
分別於La0.7Sr0.3MnO3薄膜照射1.7MeV、3MeV不同能量之質子(Proton;H+)及以10KeV能量之質子照射La0.7Sr0.3MnO3與La0.7Ca0.3MnO3之薄膜，期望以此方法在單純之巨磁阻材料晶格中，製造『點缺陷』，這些缺陷將使得Hund耦合減弱，或產生其他加強或減弱磁阻效應(如SFT)之機制，得以更瞭解磁阻之效應。
使用之薄膜乃以PLD（Pulse Laser Deposition）成長，再將薄膜蝕刻成微橋狀，使得樣品在進行離子轟擊時能夠確保劑量均勻。
此後再進行基本之電性量測，如R-T曲線，及定溫磁阻量測，配合一部份之霍爾量測，以辨明此材料之導電機制與特性及瞭解磁阻材料與理論－Double Exchange、John-Teller effect、Spin Polarlized Tunneling…等之相關性。

Abstract
It is know that the crystal structure and the magnetic ordering in La1-xAxMnO3(A=Ca,Sr,Ba) may disrupted by introducing various defect. This disorder weakens the Hund coupling and, thus, the double-exchange interaction between Mn3+ and Mn4+. Combining with John-Teller distortion enhanced by the defects, the magnetoresistance (MR) effect is enhanced. Up to date, the generated defects were mostly columnar defects or chemical substitution defects. In this study we generated different type of defect, point defects, and inrestigate its effect on MR effect.
La0.7Sr0.3MnO3 and La0.7A0.3MnO3 films were deposit on LaAiO3 (001) and SrTiO3 (001) substrates by pulse laser deposition technique. Films were patterned with a standard photolithography. Point defects were introduced by irradiated high (1.7 and 3MeV) and low (10KeV) energy protons.
We found that, the low dose sample exhibits both conductivity and the low field MR enhancement. Which were believed due to introduce acceptor level and the magnetic structure defects. When the dose was high, the structure defects leaded strong scattering effect that lowed the conductivity. The MR in high dose sample was also enhanced near by transition temperature.

圖目錄 -----------------------------------------Ⅲ
表目錄 -----------------------------------------Ⅴ

第一章 簡介 -----------------------------------1
第二章 磁性物質理論基礎 -----------------------5
第一節 順磁性 ---------------------------------5
第二節 鐵磁性 ---------------------------------8
第三節 反鐵磁性 ------------------------------10
第三章 材料物理特性 --------------------------11
第一節 晶格結構 ------------------------------11
第二節 特性相圖與磁阻(MR)特性 ----------------13
第三節 雙交換交互作用 ------------------------15
第四節 John-Teller Effect --------------------17
第五節 低磁場巨磁阻效應 ----------------------19
第六節 磁雜質引起之自旋反轉 ------------------20
第七節 點缺陷之效應 --------------------------22
第四章 實驗方法與量測系統架設-----------------24
第一節 實驗方法 ------------------------------24
第一項 薄膜製備 ------------------------------25
第二項 黃光製程 ------------------------------25
第三項 人工製成點缺陷 ------------------------27
第四項 電性之量測 ----------------------------28
第二節 量測系統架設 --------------------------29
第一項 量測儀器 ------------------------------29
第二項 溫度控制系統 --------------------------30
第三項 量測程式撰寫 --------------------------33

第五章 結果與討論 --------------------------- 36
第一節 La0.7Sr0.3MnO3，1.7MeV與3MeV質子束照射 36
第二節 10KeV質子之植入------------------------42
第一項 La0.7Ca0.3MnO3-------------------------43
第二項 La0.7Sr0.3MnO3-------------------------57
第六章 結論 ----------------------------------57

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