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Reversal Dynamics of Magnetic Vortex Core in Soft Magnetic Nanoelements : 연자성 나노물질에서의 자기소용돌이 핵의 자화 반전 연구

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dc.contributor.advisor김상국-
dc.contributor.author유명우-
dc.date.accessioned2017-07-13T05:45:32Z-
dc.date.available2017-07-13T05:45:32Z-
dc.date.issued2015-02-
dc.identifier.other000000026161-
dc.identifier.urihttps://hdl.handle.net/10371/117999-
dc.description학위논문 (박사)-- 서울대학교 대학원 : 재료공학부, 2015. 2. 김상국.-
dc.description.abstractThis thesis addresses dynamics of ultrafast magnetic vortex core switching (≤ 1 ns) in soft magnetic nanoelements by micromagetic simulations. To find more efficient way to reverse the core magnetization, we used the radial and azimuthal spin-wave modes in thin magnetic nanodisks. We also examined the core switching in three-dimensional magnetic half-spheres.
First, we observed the radial spin-wave mode driven vortex core reversals using oscillating magnetic fields applied perpendicularly to the disk plane. It was found that when the field frequencies are tuned to the eigenfrequencies of radial spin-wave modes of the vortex structure, the threshold field amplitudes required for vortex-core switching are an order of magnitude smaller than those of static perpendicular fields within 1 ns. The reversal mechanism and associated underlying physics are completely different from well-known vortex-antivortex-pair-mediated core reversals.
Next, we also examined the azimuthal spin-wave modes driven vortex-core switching in soft magnetic nano-disks. We addressed the similarities and differences between the asymmetric core reversals in terms of the temporal evolutions of the correlated core-motion speed, locally concentrated perpendicular gyrofield, and magnetization dip near the original vortex core. The core-motion speed and the associated perpendicular gyrofield must reach their threshold values to meet the ultimate core-reversal criterion mz,dip ~ -p , where p is the polarization of the given vortex state. Also, we determined the perpendicularly bias field strength and direction dependence of the core-switching time and threshold exciting field strength required for the core reversals, which parameters are essential in the application aspect.
Finally, we studied the magnetization-reversal dynamics of soft magnetic half-spheres with vertically non-uniform vortex cores, and found a heretofore-unknown mechanism of vortex-core reversals in cylindrical dots. In the half-sphere geometry, another vortex core, the magnetization of which is opposite to the original core, is formed at the edge of the half-sphere after expulsion of the original core, thereby reversing the core. Core switching occurs either with or without chirality switching. The specific curved three-dimensional geometry of half-spheres can affect the core-reversal mechanisms.
The present studies offer deeper insights into the core switching dynamics as well as imparts further momentum to the realization of information storages based on the vortex structure and its dynamic properties.
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dc.description.tableofcontentsChapter 1 Introduction
References
Chapter 2 Research Background
2.1. Magnetic Vortex
2.1.1. Magnetic Vortex State
2.1.2. Eigenmodes in the Magnetic Vortex
2.2. Vector Network Analyzer (VNA)
2.2.1. VNA-FMR Measurement
2.2.2. Reflection VNA-FMR technique
2.2.3. Transmission VNA-FMR technique
2.3. Numerical Calculations for Spin Dynamics
2.3.1. Micromagnetics
2.3.2. Micromagnetic Simulations
References
Chapter 3 Spin-wave Modes in the Magnetic Vortex State
3.1. Introduction
3.2. Methods
3.2.1. Experimental Method
3.2.2. Micromagnetic Simulation Method
3.3. Results and Discussion
Appendix
References
Chapter 4 Radial Mode Driven Core Switching in Nanodisks
4.1. Introduction
4.2. Modeling
4.3. Results and Discussion
4.3.1. Eigenfrequencies of the Radial Spin-wave Modes
4.3.2. Radial Spin-wave Mode Driven Vortex Core Switching
4.3.3. Threshold Field and Switching Time
References
Chapter 5 Azimuthal Mode Driven Core Switching in Nanodisks
5.1. Introduction
5.2. Modeling
5.3. Results and Discussion
5.3.1. Azimuthal-mode-driven core reversals
5.3.2. Control of core reversals by perpendicular bias field
References
Chapter 6 Vortex Core Switching in Magnetic Half-spheres
6.1. Introduction
6.2. Modeling
6.3. Results and Discussion
6.3.1. Eigenmodes in a Magnetic Half-spheres
6.3.2. Gyrotropic Mode Driven Vortex Core Switching
References
Chapter 7 Summary

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dc.formatapplication/pdf-
dc.format.extent3633327 bytes-
dc.format.mediumapplication/pdf-
dc.language.isoen-
dc.publisher서울대학교 대학원-
dc.subjectMagnetism-
dc.subjectSpin Dynamics-
dc.subjectMagnetic Vortex-
dc.subjectVortex Core Switching-
dc.subject.ddc620-
dc.titleReversal Dynamics of Magnetic Vortex Core in Soft Magnetic Nanoelements-
dc.title.alternative연자성 나노물질에서의 자기소용돌이 핵의 자화 반전 연구-
dc.typeThesis-
dc.description.degreeDoctor-
dc.citation.pagesx, 133-
dc.contributor.affiliation공과대학 재료공학부-
dc.date.awarded2015-02-
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