Influence of uniaxial anisotropy on the domain pinning fields in ferromagnetic Ga1-xMnxAs films
- 주제(키워드) domain pinning fields , magnetic anisotropy , ferromagnetic semiconductor
- 발행기관 고려대학교 대학원
- 지도교수 이상훈
- 발행년도 2011
- 학위수여년월 2011. 2
- 학위구분 석사
- 학과 일반대학원 물리학과
- 원문페이지 55 p
- 실제URI http://www.dcollection.net/handler/korea/000000025159
- 본문언어 영어
- 제출원본 000045642331
초록/요약
This thesis focused on the influence of uniaxial anisotropy on the domain pinning fields of ferromagnetic Ga1-xMnxAs films. The domain pinning fields of ferromagnetic Ga1-xMnxAs films were investigated using the planar Hall effect (PHE). Two in-plane components of GaMnAs films` anisotropy fields ( and ), which determine the direction of magnetic easy axes in the (001) plane, were obtained from the PHE`s angular dependence fitted with magnetic free energy within the scheme of the Stoner-Wohlfarth model. Since the cubic anisotropy ( ) is dominant at low temperature in GaMnAs, the effect of uniaxial anisotropy ( ) is normally ignored in the calculation of domain pinning field. In this study, the domain pinning fields were obtained both with and without consideration of the deviation angle of magnetic easy axes from the <100> crystallographic direction given as of each sample, where KC and KU are cubic and uniaxial anisotropy constants. The values of domain pinning fields are clearly different between the two methods of analysis and the discrepancy increases with . This indicates that the correct direction of the magnetic easy axis (i.e., the influence of uniaxial anisotropy) must be considered to obtain precise values of pinning fields in GaMnAs films. The results show a systematic increase (decrease) of domain pinning fields for crossing uniaxial hard (easy) direction as the deviation angle increases.
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CONTENTS
ABSTRACT…………………………………………………………………4
CONTENTS………………………………………………………………………6
FIGURES…………………………………………………………………………8
TABLES…………………………………………………………………………10
CHAPTER 1 INTRODUCTION………………………………………………11
1.1 Motivation…………………………………………………………11
CHAPTER 2 THEORIES ……………………………………………………13
2.1 Diluted magnetic Semiconductor……………………………………13
2.2 The Hall Effect of ferromagnetic film………………………………16
2.3 Magnetic Anisotropy of Ga1-xMnxAs………………………………19
2.3.1 Uniaxial anisotropy………………………………………20
2.3.2 Cubic anisotropy…………………………………………21
2.4 Free Energy density…………………………………………………24
2.4.1 In-plane Free Energy density……………………………25
2.4.2 Out-of-plane Free energy density………………………27
2.5 The domain Pinning field: Cowburn Model………………………28
CHAPTER 3 SAMPLE PREPARATION AND EXPERIMENTAL SETUP
……………………………………………………………………………………30
3.1 Sample preparation…………………………………………………30
3.2 Planar Hall effect measurement setup………………………………33
CHAPTER 4 RESULTS AND DISCUSSION………………………………36
4.1 Determination of deviation angle of magnetic easy axes…………36
4.2 Domain pinning fields………………………………………………42
4.3 Influence of uniaxial anisotropy……………………………………48
CHAPTER 5 CONCLUSION…………………………………………………52
REFERENCES…………………………………………………………………53
