As and Epitaxial-Growth MnSi Thin Films - OPUS Würzburg

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50 4. Epitaxial lift-off of (Ga,Mn)As thin films H 3390 3380 3370 3360 270 3360 3370 3380 3390 0 315 225 180 45 90 135 70 nm (Ga,Mn)As on 30 nm STO J H 14920 14900 14880 14860 14840 14860 14880 14900 14920 270 315 225 0 180 70 nm as-grown J 45 135 90 Fig. 4.6: Saturation magnetization measurements with rotating in-plane applied field. Both devices have current flowing along the [110] direction. The lifed-off layer shows a dominant uniaxial hard axis along the current direction at 45 ◦ , compared with the as-grown layer (on top of the AlAs sacrificial layer) with resistance maximum along 0 ◦ [100] and 90 ◦ [010]. in the as-grown layer (AlAs sacrificial layer) to rotating towards the [110] direction as the sample is placed on top of the 30-nm STO tunnel barrier. The lattice constant of crystalline STO is at ≈ 0.3905 nm, which is at least 30% smaller than the GaAs lattice constant a GaAs = 0.565 nm. Aside from the possibility of the strain being released on the material as it is removed from the AlAs barrier, a sizeable compressive strain might also be the reason for the rotation of the anisotropies and reduction into a single hard axis for the lifted-off layer. Indeed several studies have already been done on the effect of strain on the magnetic anisotropies in (Ga,Mn)As.[Weni 07, Hump 07] In order to further check the types of anisotropies present in the lifted-off material, we also perform variable field measurements at different angles. Shown in Figure 4.7 are the the resistance polar plots (RPP) for a lifted-off 70 nm layer on STO/Si and a reprinted reference RPP for a 70 nm (Ga,Mn)As layer from [Papp 07a]. The lifted-off layer shows the typical elongation along [110], suggesting uniaxial contribution to the anistropic magnetoresistance along [110], also clear from Figure 4.6. This behavior actually places the lifted-off layer closer to (Ga,Mn)As grown on GaAs substrate, suggesting release of stress from the sacrifical layer instead of a large lattice mismatch resulting in large compressive strain. Indeed, strain relaxation is observed in [Greu 11] as the (Ga,Mn)As is released from the sacrificial layer. As a final test of the differences in the magnetic anisotropies in the as-grown and lifted-off layers, we perform low-field Hall measurements. From Figure 4.8, a substantial difference between the switching fields for the as-grown and ELO layers is observed in out-of-plane Hall measurements. The result is consistent with [Greu 11]. The release of the stress from the AlAs sacrificial layer was shown to reduce the saturation field for the magnetization.
4.4. Magnetotransport in ELO-processed (Ga,Mn)As Films 51 From the MR and Hall measurements, we see that the ELO process preserves the general features of the (Ga,Mn)As 70-nm as-grown film, particularly the magnetic anisotropy, 60 40 20 0 20 40 60 60 40 20 0 20 40 60 Fig. 4.7: Resistance polar plots for 70 nm (Ga,Mn)As thin films. On the left is the resistance polar plot for a 70 nm (Ga,Mn)As film deposited via ELO on top of 30-nm thick STO on n-type Si. The plot shows uniaxial contribution along the [110] and clear biaxial contribution. On the right is a reprinted reference RPP for a film of similar thickness grown on GaAs from [Papp 07a], showing uniaxial contribution along [¯110]. Reprinted image from [Papp 07a]. 400 200 STO 30 nm 20000 10000 as-grown RHall( ) 0 -200 R Hall ( ) 0 -10000 -400 -0.3 -0.2 -0.1 0.0 0.1 0.2 0.3 Magnetic Field (T) -20000 -0.3 -0.2 -0.1 0.0 0.1 0.2 0.3 Magnetic Field (T) Fig. 4.8: Magnetization measurements with out-of-plane applied field and current along GaAs[110] for both samples. There is a marked difference in the switching fields between both measurements, showing reduction on the ELO-transferred layer on top of a 30-nm thick STO layer. (H 30nmSTO ≈ 50mT versus H as−grown ≈ 100mT) The change is consistent with observations from [Greu 11]. The difference in the resistance values might arise from the difference in the signal extraction for both sets of data. The as-grown layer was measured directly from transverse contacts while for the ELO layer the signal had to be extracted from out-of-plane magnetoresistance measurements.
Page 1 and 2:
Characterization of Novel Magnetic
Page 3 and 4: Contents Zusammenfassung 4 Summary
Page 5 and 6: Zusammenfassung Um einerseits ein f
Page 7 and 8: Zusammenfassung 3 auf die anomale t
Page 9 and 10: Summary The study of magnetic phase
Page 11 and 12: Summary 7 bandstructure affecting t
Page 13 and 14: Chapter 1 Introduction Spin electro
Page 15 and 16: 11 states in the MnSi. Chapter 9 fi
Page 17 and 18: Chapter 2 Diluted Ferromagnetic Sem
Page 19 and 20: 2.1. Basic properties of (Ga,Mn)As
Page 21 and 22: 2.3. Electrical Control of Magnetiz
Page 23 and 24: 2.4. (Ga, Mn)As and the Metal-Insul
Page 25 and 26: 2.4. (Ga, Mn)As and the Metal-Insul
Page 27 and 28: 2.5. Summary 23 2.5 Summary A brief
Page 29 and 30: Chapter 3 Electric Control of Magne
Page 31 and 32: 3.2. Electrical control of magnetiz
Page 45 and 46: 3.3. Reproducible Conductance Fluct
Page 47 and 48: 3.4. Summary 43 changed significant
Page 49 and 50: Chapter 4 Epitaxial lift-off of (Ga
Page 51 and 52: 4.2. Test Barrier Material 47 Fig.
Page 53: 4.4. Magnetotransport in ELO-proces
Page 57 and 58: 4.5. Electrical gating of ELO-proce
Page 59 and 60: Chapter 5 Basic properties of Ferro
Page 61 and 62: 5.1. Bulk properties of MnSi 57 (a)
Page 63 and 64: 5.2. Expitaxially-grown MnSi Thin F
Page 65 and 66: 5.2. Expitaxially-grown MnSi Thin F
Page 67 and 68: 5.3. Skyrmions, Chirality and Magne
Page 69 and 70: 5.3. Skyrmions, Chirality and Magne
Page 71 and 72: 5.4. Summary 67 tions. MnSi provide
Page 73 and 74: Chapter 6 Epitaxial Growth of MnSi
Page 75 and 76: 6.2. Material Characterization 71 F
Page 77 and 78: 6.2. Material Characterization 73 M
Page 79 and 80: 6.3. Device Fabrication 75 Fig. 6.5
Page 81 and 82: 6.4. Temperature-dependent measurem
Page 83 and 84: 6.5. Summary 79 expected for the he
Page 85 and 86: Chapter 7 Magnetotransport with H
Page 87 and 88: 7.1. Hall Measurements 83 0 J || [-
Page 89 and 90: 7.1. Hall Measurements 85 0.40 R xy
Page 91 and 92: 7.1. Hall Measurements 87 is two or
Page 93 and 94: 7.1. Hall Measurements 89 6 J || [1
Page 95 and 96: 7.1. Hall Measurements 91 0.02 0.00
Page 97 and 98: 7.1. Hall Measurements 93 0.100 -55
Page 99 and 100: 7.1. Hall Measurements 95 0.15 R xy
Page 101 and 102: 7.1. Hall Measurements 97 Magnetore
Page 103 and 104: 7.2. Summary 99 T c . The sign of t
Page 105 and 106:
Chapter 8 Magnetotransport with In-
Page 107 and 108:
8.1. Magnetotransport Measurements
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Page 111 and 112:
Page 113 and 114:
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Page 119 and 120:
8.2. Summary 115 8.2 Summary Low ma
Page 121 and 122:
Chapter 9 Conclusions & Outlook In
Page 123 and 124:
Appendix A Fabrication of Four-Term
Page 125 and 126:
A.2. Optimized final process 121 Fi
Page 127 and 128:
A.2. Optimized final process 123 95
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Appendix B Epitaxial lift-off techn
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127 Evap 2 Wire Rinse in water 1min
Page 133 and 134:
Bibliography [Abra 96] E. Abrahams
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131 [Edmo 03] K. Edmonds. Journal o
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133 [Ishi 77] Y. Ishikawa, G. Shira
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135 [Mudu 05] P. K. Muduli, K.-J. F
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137 [Rich 10] A. Richardella, P. Ro
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139 [Vila 07] L. Vila, R. Giraud, L
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Acknowledgements First ofall I woul
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As and Epitaxial-Growth MnSi Thin Films - OPUS Würzburg

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