摘 要

多層反鐵磁/鐵磁薄膜之交互作用一直以來都是研究的重點。在吾人初步以混合反鐵磁La0.67Sr1.33MnO4(214)及鐵磁La0.67Ca0.33MnO3 (113)塊材之研究上，發現低磁場磁阻之增強效益極為明顯，可以進一步以多層薄膜的方式，研究穿隧磁阻(TMR)。本研究由雙層薄膜開始，在SrTiO3(100)基板上，以離軸高週波濺鍍法成長113/ 214/ STO雙層薄膜，研究磁性交互作用及磁阻特性。實驗結果顯示，在高於214之相變溫度TN時，電性已因出現的磁擾動而顯現小凸峰。溫度在小凸峰溫度之上的磁阻特性完全和一般CMR薄膜相彷，呈負磁阻的特性；但在小凸峰溫度之下卻出現完全無法理解之奇異特性，在外加電流、磁場及樣品相對位置完全相同的幾何結構下，磁阻曲線隨樣品的姿態而改變。

Abstract

The interaction between the multilayer of Antiferromagnetic(AFM)/
Ferromagnetic(FM) film have been one of the focal point in scientific and technology. In our preliminary result the enhancement on the low field magnetoresistance of AFM-La0.67Sr1.33MnO4 and FM-La0.67Ca0.33MnO3 mixture is obvious. It is, therefore, worthwhile to make it into a form of multilayer as the tunneling magnetoresistance (TMR) structure. This project was planed to start at a bilayer film of AFM-La0.67Sr1.33MnO4/ FM-La0.67Ca0.33MnO3 on SrTiO3(100) substrate by an off-axis RF sputtering system. Experiment at high temperature region (T＞70K) exhibits normal colossal magnetoresistance (CMR) behavior. A small cusp appears in R-T curve between 50~70K which is believed due to the quantum fluctuation initiated from AFM layer acted on the AFM/FM interface. However, the MR properties at this region shows abnormal phenomenon. The MR curve strongly depends on the sample posture during measurement when the relative geometry between the applied field, the applied current and the sample surface is fixed. The reason of this abnormal phenomenon is not clear yet and worth for further study .

目 錄
第一章 簡介……………………………………………….01
第二章 理論基礎……………………………..…………...03
2-1 磁阻簡介……………..…………………………...03
2-2 Double-Exchange Model……………..…………..05
2-3 Jahn-Teller distortion…………………………….08
2-4 La1-xCaxMnO3……………………………………10
2-5 La1-x Sr1+xMnO4…………………………………..14
2-6 Exchange Bias……………………………………20
第三章 實驗方法………………..……………………...….21
3-1 實驗儀器設備之簡介……………………………..21
3-1-1 薄膜製程之濺鍍系統………………….….21
3-1-2 電性及磁阻量測系統……………………..23
3-2 樣品製備……………………………………….….28
3-3 電性及磁阻量測…………………….……………..30
第四章 結果與討論…………………………..……………….31
4-1 雙層薄膜特性……………….……………….....….…..31
4-2 薄膜品質……..………………………………………..33
4-2-1 La0.67Ca0.33MnO3 (113)………………………33
4-2-2 La0.67Sr1..33MnO4 (214)……..…….………....35
4-3 雙層薄膜電性量測…………………………...….…..37
4-4 雙層薄膜磁阻量測…………….…………………..40
4-4-1 垂直磁場…………….……………………...40
4-4-2 平行磁場……………………………….…...42
4-4-3 垂直磁場-樣品(90o)………………………...45
4-5 雙層薄膜交換磁異向性量測…………...…………...46
4-6 數據驗證……………………………………...………47
第五章 結論………………………………………………..….49
參考資料 ………………………………………………………50
附錄 ………………………………………………………52

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