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Micromagnetic study on magnetization dynamics considering spin-orbit interaction

  • 문정환 (대학원 신소재공학과 신소재공학전공)

초록/요약

In 1996, Slonczweski and Berger predicted the spin-transfer torque. When the current flows through ferromagnetic materials, the current is spin-polarized and carry spin angular moment. It can be transferred to the local magnetization in magnetic materials and exert a torque on the magnetization. In addition to the physical interest on this subject, it opens the new era of spintronics taking advantage of magnetization dynamics such as full magnetization reversal, steady-state precession, current induced domain wall motion, and modification of spin-wave properties. In the first part of this thesis, the current-induced resonant excitation of a magnetic vortex core is investigated by means of analytical and micromagnetic calculations. We find that the radius and phase shift of the resonant motion are not correctly described by the analytical equations because of the dynamic distortion of a vortex core. In contrast, the initial tilting angle of a vortex core is relatively free from the distortion and is affected by the nonadiabaticity of the spin-transfer torque. Thus, the nonadiabaticity can be determined experimentally by measuring the very initial motion of a vortex core. In the second part, we theoretically investigate the spin-motive force generated by a gyroscopic motion of a magnetic vortex in the presence of Rashba spin-orbit coupling.We show that the Rashba spin-orbit coupling induced spin-motive force depends not only on the polarity of a vortex core but also on the chirality of a vortex. Both polarity and chirality can be simultaneously determined by measuring voltage difference between two electrodes. The proposed method may be useful to electrically read the information of a magnetic vortex (polarity and chirality) for device applications, and to estimate the strength of Rashba spin–orbit coupling ina ferromagnet even when it is small. In the third part, we show the effect of interfacial Dzyaloshinskii-Moriya interaction on spin wave properties. Analytic expressions for spin-wave properties show that the interfacial Dzyaloshinskii-Moriya interaction leads to nonreciprocal spin-wave propagation, i.e., different properties for spin waves propagating in opposite directions. In favorable situations, it can increase the spin-wave attenuation length. Comparing measured spin-wave properties in ferromagnet/normal metal bilayers and other artificial layered structures with these calculations could provide a useful characterization of the interfacial Dzyaloshinskii-Moriya interactions. We also propose the experimental method to determine the magnitude of Dzyaloshinskii-Moriya interaction by measuring the frequency shift.

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목차

Abstract
1 Theoretical Background
1.1 Introduction
1.2 Spin-transfer torque
1.2.1 Spin-transfer torque in spin-valve structure
1.2.2 Spin-transfer torque in collective magnetic texture
1.3 Spin-motive force
1.4 Micromagnetic modeling
2 Current-induced resonant motion of a mangetic vortex core : effect of nonadiabatic spin torque
2.1 Background
2.2 Analytical approach
2.3 Micromagnetic modeling
2.4 Results and discussions
2.5 Summary
3 Electrical detection of polarity and chirality of a magnetic vortex using spin-motive force caused by Rashba spin-orbit coupling 25
3.1 Background
3.1.1 Spin-motive force
3.1.2 Enhanced spin-motive force induced by Rashba spin-orbit coupling
3.2 Analytical approach
3.3 Modeling results and discussions
3.4 Summary
4 Spin-wave propagation in the presence of interfacial Dzyaloshinskii-Moriya interaction
4.1 Background
4.1.1 Dzyaloshinskii-Moriya interaction
4.1.2 Spin-wave theory
4.2 Modeling results and discussions
4.3 Summary
Appendices
A Effect of enhanced damping due to spin-motive force on
field-driven domain wall motion
B Effect of enhanced damping caused by spin-motive force on vortex dynamics
Bibliography
Curriculum Vitae

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