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Magnetic vortex based magnons in one-dimensional periodic arrays of soft ferromagnetic nanodisks : 일차원 강자성 나노 디스크 배열구조에서 자기소용돌이 기반의 마그논 연구
DC Field | Value | Language |
---|---|---|
dc.contributor.advisor | 김상국 | - |
dc.contributor.author | 한동수 | - |
dc.date.accessioned | 2017-07-13T05:39:15Z | - |
dc.date.available | 2017-07-13T05:39:15Z | - |
dc.date.issued | 2014-02 | - |
dc.identifier.other | 000000017079 | - |
dc.identifier.uri | https://hdl.handle.net/10371/117924 | - |
dc.description | 학위논문 (박사)-- 서울대학교 대학원 : 재료공학부, 2014. 2. 김상국. | - |
dc.description.abstract | Abstract
Magnetic Vortex Based Magnons in One-dimensional Periodic Arrays of Soft Ferromagnetic Nanodisks Dong-Soo Han Department of Materials Science and Engineering Seoul National University Lattice vibration modes are collective excitations in periodic arrays of atoms or molecules. These modes determine novel transport properties in solid crystals. Analogously, in periodical arrangements of magnetic vortex-state disks, collective vortex motions and vortex gyration mediated signal transport have been predicted. In this thesis, in particular, we focus on magnetic vortex-based magnonic behavior in one-dimensional (1D) periodic arrays of soft ferromagnetic nanodisks, and also provide a foundation for manipulation of the vortex-gyration based signal transfer. We, for the first time, experimentally demonstrate wave modes of collective vortex gyration in 1D periodic arrays of magnetic disks by using time-resolved scanning transmission x-ray microscopy. The observed modes are interpreted based on micromagnetic simulation and numerical calculation of coupled Thiele equations. Dispersion of the modes is found to be strongly affected by vortex polarization, chirality ordering, dimensional parameters of the constituent disk, and interdistance between neighboring disks. The effects of change in the primitive unit cells of 1D vortex arrays on collective vortex-gyration dispersion are also investigated through micromagnetic numerical and analytical calculations. As the primitive basis, we consider alternating constituent materials (NiMnSb vs. Permalloy) and alternating dimensions including constituent disk diameter and thickness. In the simplest case, that of one vortex-state disk of given dimensions and single material in the primitive cell, only a single branch of collective vortex-gyration dispersion appears. By contrast, two constituent disks different alternating materials, thicknesses and diameters yield characteristic two-branch dispersions the band widths and gaps of which differ in each case. Furthermore, we propose and demonstrate an efficient way to control coupled-vortex dynamics by means of an external perpendicular bias field. The results reveal that the dynamics properties, such as the eigenfrequencies and dispersion relations, of coupled-vortex arrays can be manipulated by the strength and direction of bias field. More interestingly, for antiparallel polarization ordering case, a single branch splits into two distinct branches under the non-zero bias field, and thus resulting in bandgap opening. This substantial work offers potential implementation into vortex-gyration based information processing devices with the advantages of endless endurance of switchable vortex states and vortex-gyration propagation, low-power signal input through resonant excitation of vortex gyrations, and low energy dissipation. Keywords: magnetic vortex, vortex dynamics, coupled dynamics, spin dynamics, magnonic crystal, spin waves Student number: 2008-20696 | - |
dc.description.tableofcontents | Abstract ii
Contents v List of Figures ix List of Tables xii Chapter1 Introduction 1 Chapter2 Research Background 5 2.1. Micromagnetics 6 2.1.1. Micromagnetic Energy 6 2.1.2 Magnetic Equilibrium and Browns Equations 12 2.1.3 Equation of motion of magnetization 14 2.2. Magnetic Vortex 17 2.2.1 What is a Magnetic Vortex 17 2.2.2 Dynamics of a Magnetic Vortex 23 2.2.3 Coupled Magnetic Vortex 25 Chapter3 Method 29 3.1 X-ray Magnetic Imaging Technique . 30 3.1.1 X-ray Magnetic Circular Dichroism (XMCD) 31 3.1.2 Full-field magnetic transmission soft X-ray microscopy (MTXM) 34 3.1.3 Scanning Transmission soft X-ray Microscopy (STXM) 37 3.1.4 Time-resolved measurement (pump-probe technique) 39 3.3 Micromagnetic simulations 40 Chapter4 Collective Vortex Oscillation Modes in a 1D chain Consisting of a Single-component Constituents 42 4.1 Sample preparation and experimental setup 43 4.2 Vortex-core gyration propagation along dipolar-coupled disks 46 4.3 Numerical calculation of N coupled Thiele equations for N coupled vortex gyrations 49 4.4 Discrete wave modes of collective vortex gyration in finite number of disks 53 4.4.1 Discrete wave modes for N coupled-vortex dynamics 53 4.4.2 Discrete wave modes in real sample 57 4.5 Dispersion relations of collective vortex gyration in 1D arrays of finite number of disks 61 4.6 Dispersion relation in 1D magnetic vortex-based magnonic crystal of infinite or semi infinite number of disks 65 4.7 Phase relation of the net in-plane magnetizations between the NN disks and dispersion relations 70 Chapter5 Collective Vortex Oscillation Modes in a 1D Chain Consisting of Bi-component Constituents 73 5.1 Model geometry 74 5.2 Vortex-core gyration propagation in the 1D chain consisting of bicomponent constituents 77 5.3 Dispersion relations in the 1D chain consisting of Bi-component Constituents 80 5.3.1 Micromangetic simulations results 80 5.3.2 Analytical derivation of dispersion relations 83 5.4 Spatial profiles of coupled core motions for specific collective gyration modes 86 5.5 Different types of basis and their dispersion relations 89 Chapter6 Bias field control of N-body coupled vortex oscillation 92 6.1 Perpendicular bias field effect on an isolated disk 94 6.2 Dipolar interaction and interaction integrals under the influence of perpendicular bias field 97 6.3 Normal modes in two coupled vortex oscillator under the influence of perpendicular bias field 100 6.4 Dispersion relation of 1D arrays of coupled vortex oscillators under the influence of perpendicular bias field 107 Chapter7 Summary 110 Appendix A. Experimental Setup 112 A.1 Thin film deposition 112 A.2 Lithography 114 A.3 Electrical measurement setup 118 Bibliography 122 Publication List 131 Patent List 135 International Conference Presentations 136 Domestic Conference 139 | - |
dc.format | application/pdf | - |
dc.format.extent | 6002440 bytes | - |
dc.format.medium | application/pdf | - |
dc.language.iso | en | - |
dc.publisher | 서울대학교 대학원 | - |
dc.subject | magnetic vortex | - |
dc.subject | vortex dynamics | - |
dc.subject | coupled dynamics | - |
dc.subject | spin dynamics | - |
dc.subject | magnonic crystals | - |
dc.subject | spin waves | - |
dc.subject.ddc | 620 | - |
dc.title | Magnetic vortex based magnons in one-dimensional periodic arrays of soft ferromagnetic nanodisks | - |
dc.title.alternative | 일차원 강자성 나노 디스크 배열구조에서 자기소용돌이 기반의 마그논 연구 | - |
dc.type | Thesis | - |
dc.description.degree | Doctor | - |
dc.citation.pages | 147 | - |
dc.contributor.affiliation | 공과대학 재료공학부 | - |
dc.date.awarded | 2014-02 | - |
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