Investigation of Pinning Field Distribution in Ga1-xMnxAs Ferromagnetic Semiconductor Film
- 주제(키워드) GaMnAs , distribution , pinning field , ferromagnetic
- 발행기관 고려대학교 대학원
- 지도교수 이상훈
- 발행년도 2009
- 제출일 2009-01-06
- 학위수여년월 2009. 2
- 학위명 석사
- 학과 일반대학원 물리학과
- 세부전공 고체물리전공
- 원문페이지 61 p
- 실제URI http://www.dcollection.net/handler/korea/000000007585
- 본문언어 영어
- 제출원본 000045534457
초록/요약
This thesis focused on the distribution of domain pinning fields in Ga1-xMnxAs ferromagnetic semiconductor film. A ferromagnetic Ga1-xMnxAs film with x=0.062 and a thickness of 100 nm, used in this study, was grown in a molecular beam epitaxy (MBE) machine. A piece of Ga1-xMnxAs film was annealed at 250 °C for 1 hour in air. The angle dependence of the planar Hall effect (PHE) has been measured and analyzed based on the magnetic free energy model, which consists of magnetic anisotropies and Zeeman effects. The only a single energy minimum exists along the external magnetic field direction under high field relative to magnetic anisotropies due to the dominant Zeeman effects. This leads to the coherent rotation of the magnetization in the form of a single domain state in both as-grown and annealed samples. On the other hand, the behavior of both samples is significantly different under relative low magnetic field. When field strength is reduced, other energy minima appear due to the nature of biaxial magnetic anisotropies. While the magnetization switches abruptly between the two energy minima in the as-grown sample, it changes gradually from one state to the other in the annealed sample. This different reversal behavior of magnetization is well understood by distribution of magnetic domain pinning fields. The pinning field distribution of the as-grown sample is localized on narrow region, which leads to behave like single domains in entire sample. In contrast, the pinning fields of the annealed sample have a wide distribution. This study provides valuable information on the magnetic domains in ferromagnetic Ga1-xMnxAs films.
more목차
Abstract 1
Contents 2
Figures 5
Chapter 1: Introduction 9
1.1 Spintronics 9
1.2 Diluted Magnetic Semiconductor: Ga1-xMnxAs 10
Chapter 2: Sample Preparation and Experiments 12
2.1 Sample Preparation 12
2.2 Setup for Magnetotransport Measurement 15
Chapter 3: Theories 17
3.1 Hall Effect of Ferromagnetic Material 17
3.2 Free Energy Density 20
3.3 Pinning Energy: Cowburn Model 23
Chapter 4: Quantitative Analysis of PHE 25
4.1 Introduction 25
4.2 Magnetization Reversal Process 26
4.3 Pinning Field Dependence of Magnetic Field 33
Chapter 5: Distribution of Pinning Fields 37
5.1 Introduction 37
5.2 Pinning Field Distribution: Single and Multi Phase 38
Chapter 6: Summary 53
References 55
