Title Page
Abstract
Contents
Chapter 1. Introduction 14
1.1. Dzyaloshinskii-Moriya Interaction 15
1.2. Conventional ferromagnetic systems exhibiting PMA 16
1.3. Magnetic domains and DWs 17
1.4. DW dynamics in creep regime 18
1.5. Types of chiral DW induced by DMI 22
1.6. Asymmetric DW speed scheme for DMI measurement 23
Chapter 2. Experimental setup 26
2.1. Branch of interfacial phenomena and challenges 27
2.2. Approach for isolating single interface 28
2.3. Magneto-optical Kerr effect (MOKE) 29
2.4. In-vacuum MOKE system 30
2.5. Verification of DW creep in single interface systems 32
Chapter 3. Magnetic layer thickness dependence of DMI 36
3.1. Background 37
3.2. Sample fabrication 38
3.3. Magnetic layer thickness dependence of DMI 39
Chapter 4. Non-magnetic layer thickness dependence of DMI 40
4.1. Background 41
4.2. Sample fabrication 41
4.3. Non-magnetic layer thickness dependence of DMI 42
4.4. Correlation between DMI and lattice constant 46
4.5. Utilization of the correlation: chirality engineering 49
Chapter 5. Formation of interface and DMI 52
5.1. Background 53
5.2. Experimental approach 53
5.3. Layer-resolved contributions of DMI 56
5.4. Universal length of interface: transition from surface to interface 64
Chapter 6. DW roughness scheme for DMI measurement 68
6.1. Background 69
6.2. Sample fabrication 69
6.3. Determination of DW roughness 70
6.4. Quantification of DMI from DW roughness 74
Chapter 7. Conclusion and outlook 77
References 79
Author's Biography 87
국문 초록 93
Figure 1.1. Schematic of the atomic geometry of DMI. a, Counterclockwise chirality. b, Clockwise chirality. 15
Figure 1.2. Schematic of conventional system. a, diagram of layered structure. b, magnetic domains, and domain-walls (DWs) on the film. 17
Figure 1.3. Schematic diagram of magnetization configuration inside DWs. 18
Figure 1.4. Plot of vDW as a function of Hz−µ with µ=1/4. The solid line is the best fitting of the creep scaling law.[이미지참조] 20
Figure 1.5. Plot of creep scaling constant α with respect to effective Co thickness tCo − tDead for the series of films of Pt/Co/Pt (black) and Pt/Co/TiO₂/Pt (red)....[이미지참조] 21
Figure 1.6. Graphic illustration of three distinct chirality of DW. Each DW type is denoted in the figure. The green symbols indicate the magnetization direction... 22
Figure 1.7. Schematic drawings of Eqs. (1.3) and (1.4) with respect to Hx. The green vertical line indicates the symmetric axis, corresponding to −HDMI.[이미지참조] 24
Figure 1.8. Plot of vDW with respect to Hx for different DW chirality. a, CW, b, Bloch, and c, CCW. The colored vertical line indicates the positions of their...[이미지참조] 25
Figure 2.1. Schematic of interfacial phenomena and conventional magnetic structures. 27
Figure 2.2. Schematic of isolating single interface. 29
Figure 2.3. Schematic diagram of MOKE. The polarization of the lights (pink arrows) reflected from up-domain (grey) and down-domain (black) regions,... 30
Figure 2.4. Schematics of experimental setup of in-vacuum MOKE system. The system consists of the deposition chamber, characterization chamber, MOKE... 32
Figure 2.5. MOKE image of domains in Pt(2.5)/Co(0.8). The grey (black) region indicates up (down) domain. 33
Figure 2.6. Plot of vDW as a function of H⁻¹/⁴ from tCo=0. 5 nm to tCo=1. 4 nm. The solid lines indicate the best fitting with the creep-scaling law.[이미지참조] 34
Figure 2.7. Plot of α with respect to tCo (black) and tCoeff (red) respectively. The solid lines indicate the best linear fitting, and the vertical black dashed line...[이미지참조] 35
Figure 3.1. Schematic of sample structures of Pt/Co. 38
Figure 3.2. Plot of HDMI with respect to tCo. The dashed line guides the eyes.[이미지참조] 39
Figure 4.1. Schematic of sample structures of Pt/Co. 42
Figure 4.2. Plots of vDW as a function of Hx with constant Hz for the Pt/Co single interface films with different tPt. The red vertical line indicates the...[이미지참조] 43
Figure 4.3. Plots of HDMI and D with respect to tPt. a, Plot of HDMI with respect to tPt. b, Plot of D with respect to tPt. The dashed line in each panel...[이미지참조] 45
Figure 4.4. XRD spectra for the films with different tPt. The spectra near the Pt fcc (111) peak are shown. The colored vertical line indicates the peak position....[이미지참조] 46
Figure 4.5. Correlation between c and D. a, Plot of c with respect to tPt. The black dashed horizontal line indicates the bulk value of the Pt fcc (111) lattice...[이미지참조] 48
Figure 4.6. Plots of vDW as a function of Hx with constant Hz for the Pt/Co/Pt tri-layered films with different tPt . The colored vertical line indicates the...[이미지참조] 50
Figure 5.1. Schematic diagram of deposition process of various materials X. The used materials X is denoted in the figure. 54
Figure 5.2. Methodology for deriving the layer-resolved contributions of interfacial DMI. a, Measurement of HDMI in structure of Pt(2.5)/Co(0.9) single...[이미지참조] 55
Figure 5.3. Plot of HDMITot and HDMIx with respect to tx for X=Al.[이미지참조] 57
Figure 5.4. Plot of HDMITot and HDMIx with respect to tx for X=Cu.[이미지참조] 58
Figure 5.5. Plot of HDMITot and HDMIx with respect to tx for X=Nb.[이미지참조] 59
Figure 5.6. Plot of HDMITot and HDMIx with respect to tx for X=Nb.[이미지참조] 60
Figure 5.7. Plot of HDMITot and HDMIx with respect to tx for X=Hf.[이미지참조] 61
Figure 5.8. Plot of HDMITot and HDMIx with respect to tx for X=Ta.[이미지참조] 62
Figure 5.9. Schematic diagram of the coverage of the deposition process. 63
Figure 5.10. Plot of theoretical D with respect to number of Ta layer from the first-principles calculation for the Pt(3 ML)/Co(3 ML)/Ta(0-3 ML) structures. 64
Figure 5.11. Plot of ∑HDMIx /HDMIxTot with respect to tx. The blue region indicates surface dominant regime. The purple region indicates transition...[이미지참조] 66
Figure 6.1. Schematic drawing of DW writing process. a, Schematic drawing of the sample with the magnetic wire (light gray area) and gold wire (yellow area).... 71
Figure 6.2. Determination of DW roughness. a, MOKE images for Hx=0. b, MOKE images for Hx=182 mT. c, The histogram of w for Hx=0 (green)...[이미지참조] 73
Figure 6.3. Quantification of DMI based on DW roughness and DW asymmetric speed for the Pt/Co/Pt film. a, Plot of w(Hx) with respect to Hx. b, Plot of...[이미지참조] 75