臺灣博碩士論文加值系統

本研究選用鑭鋁氧(110)與鈦酸鍶(100)兩種基板，利用雷射濺鍍分別
製備b軸與c軸垂直基板的正交結構鉺錳氧薄膜，並研究其結構與磁特性。我們發現三個磁性轉折點，第一個轉折點發生於42K為尼爾溫度，是由錳的反鐵磁磁序引起的；第二轉折點可能為錳的自旋重新排列所導致的成長於兩種基板上的鉺錳氧其第二個轉折溫度有很大的不同；最後一個出現在低溫的轉折係因稀土元素鉺所引發的。其中，尼爾溫度和鉺的轉折不會因成長的基板而有所不同，然而錳的自旋重新排列轉折在不同的基板上卻有10K的差距，這可能是由於成長於不同基板上取向附生的應力所造成的差異。此外我們也針對低氧壓環境下製備薄膜會造成的影響做了討論。

We have investigated the structure and magnetic properties of b and c-axis-oriented multiferroic orthorhombic ErMnO3 (o-ErMO) films deposited on LaAlO3(110) and SrTiO3(001) substrate, respectively, by pulsed laser deposition. Three distinctive magnetic transitions were observed for o-ErMO films grown on both LAO and STO substrates. The first one locating around 42K is apparently associated to the antiferromagnetic ordering of Mn moment and, thus, it is assigned as the Neel temperature (TN). The second transition was observed near 18K for o-ErMO/LAO(110), which is markedly different from the transition at 28K for o-ErMO/STO(001). The last transition was dominated by the moments from erbium ions at lower temperatures. The two AFM transitions of Mn3+ and Er3+ moments appear to be rather insensitive to the substrates on which the films were grown. However, there is a 10-Kelvin difference in the spin reorientation transition identified for the Mn-moment when different substrates were used. This discrepancy seems to be more relevant to the strain arising from film/substrate epitaxy. Besides, in order to clarify the effect of low oxygen partial pressures on the magnetic structure, we also compare the structure and magnetic properties of the o-ErMO films prepared under very different oxygen partial pressures.

Table of Contents
Abstract (In Chinese) i
Abstract (In English) ii
Acknowledgement iv
Table of Contents v
List of Tables vi
List of Figures vii
Chap.1 Introduction 1
1.1. Background 1
1.2. Motivation 5
Chap.2 Fundamental physical properties of RMnO3 manganites 6
2.1 Superexchange 6
2.2 Double Exchange 8
2.3 Crystal Field Effect 9
2.4 Jahn-Teller Effect 11
2.5 Crystal structure of orthorhombic RMnO3 13
2.6 Model for magnetic structure of orthorhombic RMnO3 14
Chap.3 Experiments 18
3.1 Sample Preparation 18
3.1.1 Target Fabrication 18
3.1.2 Pulsed Laser Deposition (PLD 18
3.2 Characterization of Thin Film 20
3.2.1 X-ray diffraction (XRD) 20
3.2.2 α step profilometer 21
3.2.3 X-ray reflectivity (XRR) 22
3.2.4 Four-circle diffractometer (Φ scan) 22
3.2.5 Superconducting Quantum Interference Device (SQUID)23
3.2.6 X-ray Absorption Near Edge Spectroscopy (XANES) 24
Chap.4 Results and Discussion 27
4.1 The structural and magnetic properties of target 27
4.2 The characterization of o-ErMO thin film 30
4.2.1 The structural properties 30
4.2.2 The magnetic properties 43
4.3 The effect of low oxygen pressure during deposition 52
Chap.5 Summary 55
References 56

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