The aim of the current thesis was to investigate the preparation of MnSi film on Si substrates. The preparation process includes room temperature sputtering Mn films with different thicknesses and flash-lamp annealing with different energy density (annealing temperature). Systematic investigations on their structural, electrical, magnetic, and magneto-transport properties were performed. The key findings are summarized below:
Thin films with the B20-MnSi phase on Si(100) substrates were fabricated for the first time. They exhibit magnetic skyrmion behaviour. In comparison with Si(111) substrates, Si(100) substrates are more preferred from the practical application point of view. The nucleation of B20-MnSi on Si(100) is believed to be triggered by the fast solid-state phase reaction between Mn and Si via ms-range flash-lamp annealing. Compared with the corresponding bulk material, our films show an increased Curie temperature of around 43 K. The magnetic and transport measurements reveal that skyrmions in B20-MnSi on Si(100) made by sub-seconds solid-state reaction are stable within much broader field and temperature windows than bulk MnSi. The parasitic MnSi1.7 phase can be further minimized or eliminated by optimizing the annealing conditions, the quality of the deposited Mn film, and its interface with the Si substrate. Our work demonstrates a promising route for the fabrication of B20-type transition metal silicides for integrated and/or hybrid spintronic applications on Si(100) wafers, which are more preferable for industry applications.
The growth of MnSi films on Si(111) substrates has been widely realized by solid phase epitaxy or molecular beam epitaxy since the lattice mismatch and symmetry fit better. One problem is the parasitic MnSi1.7 phase. By controlling the reaction parameters using strongly non-equilibrium flash lamp annealing, we have achieved full control over the phase formation of Mn-silicides in thin films from single-phase B20-MnSi or MnSi1.7 to mixed phases. The obtained films are highly textured and reveal sharp interfaces to the Si substrate. The obtained B20-MnSi films exhibits a high Curie temperature of 41 K. The skyrmion phase can be stabilized over broad temperature and magnetic field ranges. We propose flash-lamp-annealing-induced transient reaction as a general approach for phase separation in transition-metal silicides and germanides and for growth of B20-type films with enhanced topological stability.
By comparing the magnetic properties of MnSi films grown on both Si(111) and Si(100) substrates by ourselves and by others in literature, we found one common feature. It is the increased Curie temperature of around 41-43 K for all MnSi films. It is much higher than 29.5 K for bulk MnSi. We try to understand the puzzling Curie temperature widely reported in MnSi films. We have prepared MnSi films with a large variation regarding their thickness, crystallinity, strain and phase separation. Particularly, polycrystalline MnSi films on Si(100) and textured MnSi films on Si(111), both with different mixture ratio with MnSi1.7 have been grown and systematically characterized. Surprisingly, all obtained MnSi films exhibit a high Curie temperature at around 43 K. The skyrmion phase has also been detected in these films. However, we find no correlation between the increased Curie temperate and the film thickness, strain, lattice volume or the mixture with MnSi1.7. Our work has not provided a conclusive picture for this question, but is rather calling a revisit, especially to the effect by the interface, stoichiometry and point defects. Further studies are essential to understand the B20 transition-metal silicide/germanides films and therefore to utilize them for spintronic applications.:Contents
Abstract iii
Kurzfassung v
1. Introduction 1
1.1 B20 compounds and magnetic skyrmions 1
1.2 B20 MnSi with magnetic Skyrmions 8
1.2.1 Crystallization process 10
1.2.2 Phase diagram of Mn-Si binary compounds 13
1.2.3 Bulk B20-MnSi 14
1.2.4 B20-MnSi thin film 18
1.2.5 B20-MnSi nanowire 25
1.3 Fast annealing method 27
1.4 Objectives and the structure of the thesis 30
2. Experiment 32
2.1 Sample preparation 32
2.1.1 DC magnetron sputtering 32
2.1.2 Sub-second annealing 35
2.2 Structure characterization: X-ray diffraction 40
2.3 Property characterization 41
2.3.1 Magnetic properties 41
2.3.2 Magneto-transport properties 44
3. B20-MnSi films grown on Si(100) substrates with magnetic skyrmion signature 46
3.1 Introduction 46
3.2 Experiment 47
3.3 Results and Discussions 48
3.4 Conclusions 56
4. Phase selection in Mn-Si alloys by fast solid-state reaction with enhanced skyrmion stability 57
4.1 Introduction 57
4.2 Experiment 59
4.3 Results 61
4.3.1 MnSi and MnSi1.7 phase reaction 61
4.3.2 Magnetic Skyrmion 68
4.3.3 Discussion 76
4.4 Conclusion 78
5. On the Curie temperature of MnSi films 80
5.1 Introduction 80
5.2 Experiment 82
5.3 Results 83
5.4 Conclusion 89
6. Summary and outlook 90
6.1 Summary 90
6.2 Outlook 91
6.2.1 Film thickness effect on formation of (111)-textured B20-MnSi 91
6.2.2 MnSi1.7% influence on Skyrmion stability 96
6.2.3 Preparation of other transition-metal monosilicides and germanides 98
Acknowledgement 99
References 101
Publication list 117
Curriculum Vitae 119
Erklärung 120
| Identifer | oai:union.ndltd.org:DRESDEN/oai:qucosa:de:qucosa:76189 |
| Date | 08 October 2021 |
| Creators | Li, Zichao |
| Contributors | Nielsch, Kornelius, Helm, Manfred, Liu, Enke, Zhou, Shengqiang, Technische Universität Dresden |
| Source Sets | Hochschulschriftenserver (HSSS) der SLUB Dresden |
| Language | English |
| Detected Language | English |
| Type | info:eu-repo/semantics/publishedVersion, doc-type:doctoralThesis, info:eu-repo/semantics/doctoralThesis, doc-type:Text |
| Rights | info:eu-repo/semantics/openAccess |
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