As and Epitaxial-Growth MnSi Thin Films - OPUS Würzburg

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114 8. Magnetotransport with In-Plane Applied Fields 0.10 0.08 0.03 R PHE (ohm) xy 0.06 0.04 0.02 0.00 0.07 -0.3 -0.2 -0.1 0.0 0.1 0.2 0.3 Magnetic Field (T) R PHE xy (ohm) 0.02 0.01 0.00 -0.3 -0.2 -0.1 0.0 0.1 0.2 0.3 Magnetic Field (T) 0.10 R PHE (ohm) xy 0.06 0.05 0.04 R PHE xy (ohm) 0.09 0.08 0.07 -0.3 -0.2 -0.1 0.0 0.1 0.2 0.3 Magnetic Field (T) -0.3 -0.2 -0.1 0.0 0.1 0.2 0.3 Magnetic Field (T) Fig. 8.15: Antisymmetric part of the PHE signal for the 20-nm layer. Current direction is along [ 213]. ¯ Curves are from 0 to 180 degrees with 15 degree steps. Fig. 8.16: PHE curves for the 12-nm grown film with current along MnSi[¯211] and 0 degree magnetic field direction along MnSi[01-1] at various angles (0 to 180 degrees, 15 degree steps), including the antisymmetric and symmetric parts of the signals. The curves are shifted for clarity. between thesize oftheantisymmetric signal forbothsamples, ifwe combine with previous observations that the distribution of chiral domains in the grown films are different.
8.2. Summary 115 8.2 Summary Low magnetic field characterization proves to be a goodtool in probing the magnetization behavior and unraveling key difference between the grown films. For future measurements of the properties of MBE-grown MnSi thin films, variable angle low field measurements may be as important as high field in-plane and out-of-plane measurements in determining the effects of net chirality, the induced in-plane uniaxial strain [Karh 10] or spin-spin interactions [Enge 12] in the properties of these materials at the ground state. We point out the following key points in this work: • The constant-field magnetoresistance forthe 20-nmfilm shows arememory or relaxation effect which does not appear in the 12-nm film. From [Karh 10], they attribute glassy behavior of grown films through disorder and the presence of both chiral domain types in the sample. This is consistent with the higher RRR measured for the thinner film (comparable with [Li 13], indicating crystalline quality) •Themagnetoresistancefurtherexploresthedifferenceintheratiooftheexistenceofboth chiral domain in the grown samples. The 20-nmlayer shows parabolicfield (∝ H 2 ) dependence, consistent with a nearly ferromagnetic state, which is could possibly be explained with presence of both ferromagnetic and anti-ferromagnetic domains in the sample. The 12-nm film’s low field linear (∝ H) magnetoresistance also shows weak ferromagnetic behavior, which could suggest single chiral type in the thin film.[Mori 85] Longitudinal magnetoresistance curves were used to determine the effects of the measured in-planeanisotropyfromSQUIDmagnetizationmeasurements. However, polar-plotsshow no sharp switching between easy and hard axis directions for both the 20 and 12-nm layers. This probably arises from demagnetization effects caused by the shape anisotropy of the Hall bar.[Ahar 98, Baue 12] • The planar Hall effect or PHE, on the other hand, proves itself as a useful tool in determining the magnetization easy axis of the crystal. The magnetization switching shows the relative difference between the uniaxial anisotropy strengths between the two samples. For the 20-nm layer, the magnetization rotates slowly to the easy axis at a maxima of 40 mT, while the 12-nm layer shows a sharp switch at ≈ 20 mT. More importantly, thiscanalsobeameasure oftheexistence ofbothchiraldomaintypeswithinthematerial. • Symmetrization shows both a symmetric and antisymmetric part of the PHE signal. PHE, by definition in metals, should be symmetric with field through its dependence on the magnetoresistance. A plausible reason that may possibly explain the effect is an Umkehr effect (second order Hall term) arising from induced crystalline anisotropy due to strain during the growth of MnSi[111] on Si[111].[Mudu 05] Non-coplanar spins configura-
Page 1 and 2:
Characterization of Novel Magnetic
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Contents Zusammenfassung 4 Summary
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Zusammenfassung Um einerseits ein f
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Zusammenfassung 3 auf die anomale t
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Summary The study of magnetic phase
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Summary 7 bandstructure affecting t
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Chapter 1 Introduction Spin electro
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11 states in the MnSi. Chapter 9 fi
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Chapter 2 Diluted Ferromagnetic Sem
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2.1. Basic properties of (Ga,Mn)As
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2.3. Electrical Control of Magnetiz
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2.4. (Ga, Mn)As and the Metal-Insul
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2.4. (Ga, Mn)As and the Metal-Insul
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2.5. Summary 23 2.5 Summary A brief
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Chapter 3 Electric Control of Magne
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3.2. Electrical control of magnetiz
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3.3. Reproducible Conductance Fluct
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3.4. Summary 43 changed significant
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Chapter 4 Epitaxial lift-off of (Ga
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4.2. Test Barrier Material 47 Fig.
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4.4. Magnetotransport in ELO-proces
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4.4. Magnetotransport in ELO-proces
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4.5. Electrical gating of ELO-proce
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Chapter 5 Basic properties of Ferro
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5.1. Bulk properties of MnSi 57 (a)
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5.2. Expitaxially-grown MnSi Thin F
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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
Page 117: 8.1. Magnetotransport Measurements
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
Page 129 and 130: Appendix B Epitaxial lift-off techn
Page 131 and 132: 127 Evap 2 Wire Rinse in water 1min
Page 133 and 134: Bibliography [Abra 96] E. Abrahams
Page 135 and 136: 131 [Edmo 03] K. Edmonds. Journal o
Page 137 and 138: 133 [Ishi 77] Y. Ishikawa, G. Shira
Page 139 and 140: 135 [Mudu 05] P. K. Muduli, K.-J. F
Page 141 and 142: 137 [Rich 10] A. Richardella, P. Ro
Page 143 and 144: 139 [Vila 07] L. Vila, R. Giraud, L
Page 145: Acknowledgements First ofall I woul
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As and Epitaxial-Growth MnSi Thin Films - OPUS Würzburg

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