臺灣博碩士論文加值系統

摘 要
本文主要是以X光吸收光譜(X-ray Absorption Spectroscopy，XAS)及X光繞射(X-ray diffraction，XRD)，針對垂直磁異向性(Perpendicular magnetic anisotropy，PMA)的兩種奈米級磁性材料來作研究。樣品系統分別為CrPt3磊晶磁性合金薄膜以及FePt自組裝(Self-assembled)奈米磁性顆粒。
CrPt3磊晶薄膜系統之研究目的，是找尋此系統中產生垂直磁異向性(PMA)的可能原因及物理機制。實驗結果發現，垂直磁異向性產生的可能原因有二：第一、由於垂直膜面(plane-normal)與平行膜面(in-plane)部分的序化參數(order parameter)差異所導致，稱之為指向有序性(directional long-range chemical order)。第二、由延伸X光吸收精細結構(Extended X-ray absorption fine structure, EXAFS)結果發現，Cr-Cr原子配位層的鍵長，在垂直膜面(plane-normal)與平行膜面(in-plane)上的不同所引起的。
而在FePt自組裝(Self-Assembled)奈米顆粒的研究中，著重在觀察不同退火溫度下，對於奈米顆粒原子及電子結構上的影響。由EXAFS的分析結果，可以發現FePt奈米顆粒與外層包覆的介面活性劑的鍵結型態類似於Fe2O3的型態。且奈米顆粒與介面活性劑的結構，相當於Core-Shell結構。另一方面，從X光吸收近邊緣結構(X-ray absorption near edge structure, XANES)中，發現X光吸收邊緣(K-edge)隨著FePt奈米顆粒退火溫度的升高，而有往低能量移動的現象。目前推測此現象，可能是受到量子尺寸效應(quantum size effect)、表面效應(surface effect)、晶格結構變化(FCC轉變到FCT)及氧化態效應(oxidation effect)的貢獻所影響。

ABSTRACT
The author was focused on studying the advanced magnetic nano-scale materials by synchrotron X-ray absorption fine structure (XAFS) and X-ray diffraction (XRD) to understand the relationship between magnetic, atomic and electronic structure. Two different kinds of material systems in this study, namely, the CrPt3 expitaxial thin-film system, and the self-assembled FePt nanoparticles system. Both systems are the most potential materials in the future magnetic recording technologies.
CrPt3 thin films exhibit perpendicular magnetic anisotropy (PMA) and large Kerr rotation angles. In order to understand the PMA effect of the CrPt3 thoroughly, the directional chemical order S and polarization-dependent XAFS were measured. The best PMA effect can be found when the plane normal order parameter is the largest while the in-plane one is still low. At the same time, Cr-Cr bond-distance is slightly distorted by XAFS analysis. This anisotropic directional long-range chemical order might be due to the anisotropic interdiffusion and the compound formation between the Cr and Pt layer. For short-range order analysis, the PMA effect might be attributed to the difference of the Cr-Cr bond-distance between plane-normal and in-plane.
In the study of self-assembled FePt nanoparticles system, the superlattice structures and coalescence of self-assembled FePt nanoparticles were studied by XRD and XAFS techniques. During the annealing process, the XANES spectra (Fe K-edge) were found shifting to a higher energy as the annealing temperature increased. The shift of this iron K-edge might be attributed to the quantum size effect, surface effect or oxidation effect.

TABLE OF CONTENTS
ABSTRACT…………………………………………………………………………...4
ACKNOWLEDGMENT………………………………………………………………5
TABLE OF CONTENTS……………………………………………………………...6
LIST OF FIGURES……………………………………………………………………8
LIST OF TABLES……………………………………………………………………14
Chapter 1 Introduction……………………………………………………………….15
1.1 Longitudinal and Perpendicular Recording Media…………………………16
1.2 Self-Assembled Magnetic Nanoparticle Arrays…………………………….17
1.3 Magnetic anisotropy in ordered binary alloys………………………………18
Chapter 2 X-ray Absorption Fine Structure (XAFS)…………………………………19
2.1 X-ray Absorption Near Edge Structure(XANES)…………………………..20
2.2 Extended X-ray Absorption Fine Structure(EXAFS)……………………….22
2.3 Polarized-dependence XAFS……………………………………………….23
2.4 Branching ratio in XAFS……………………………………………………24
Chapter 3 Data analysis：X-ray Absorption Fine Structure…………………………26
3.1 XANES spectra simulation…………………………………………………26
3.2 EXAFS data analysis………………………………………………………..29
Chapter 4 Sample preparation………………………………………………………..31
4.1 CrPt3 epitaxial thin-films……………………………………………………31
4.2 Self-assembled FePt nanoparticles………………………………………….34
Chapter 5 CrPt3 epitaxial thin-films………………………………………………….36
5.1 Introduction of CrPt3 system………………………………………………..36
5.2 Experiment……………………………………………………………….…37
5.3 Results and Discussion……………………………………………………...38
5.4 Summary……………………………………………………………………41
Chapter 6 Self-assembled FePt nanoparticles………………………………………..53
6.1 Introduction of Self-assembled FePt nanoparticles system…………………53
6.2 Experiment………………………………………………………………….54
6.3 Results and Discussion……………………………………………………...54
6.4 Summary……………………………………………………………………58
Chapter 7 Conclusion……………………………………………………………...…69
REFERENCE………………………………………………………………………...71
APPENDIX A.1：The paper accepted by J. Magn. Magn. Mater…………………….75
APPENDIX A.2：The paper submitted to Appl. Phys. Lett………………………….76
APPENDIX A.3：The abstract submitted to the Conference on MMM’04……….….91
APPENDIX A.4：The abstract submitted to the Conference of APDSC’04…………92
APPENDIX A.5：The paper to be submitted…………………………………………93
APPENDIX A.6：物理雙月刊投稿文章…………………………………………...107
APPENDIX B.1：XRD analysis program by Visual C++ language source code……108
APPENDIX B.2：in-situ XAFS experiment setup………………………………….111
APPENDIX B.3：FEFF8.20 parameter for CrPt3(Cr K-edge) calculation………….113
APPENDIX B.4：The Raman and Fe LⅡ,Ⅲ-edge data for FePt nanoparticles……….116
APPENDIX C：Curriculum Vitae…………………………………………………...122

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