- Titel
- Defektinduzierter magnetischer Phasenübergang in CrSBr
- Zitierfähige Url:
- https://nbn-resolving.org/urn:nbn:de:bsz:14-qucosa2-1046323
- Übersetzter Titel (EN)
- Defect induced magnetic phase transition in CrSBr
- Erstveröffentlichung
- 2026
- Datum der Einreichung
- 02.02.2026
- Datum der Verteidigung
- 15.04.2026
- Abstract (EN)
- The discovery of intrinsic two-dimensional (2D) magnets such as CrI₃ and Cr₂Ge₂Te₆ has opened exciting opportunities for spintronics and quantum technologies. However, these initial 2D magnets suffer from chemical instability under ambient conditions and low magnetic ordering temperatures, necessitating encapsulation and limiting their practical application. In contrast, chromium sulfur bromide (CrSBr) has emerged as a compelling alternative: it is a van der Waals magnetic semiconductor that uniquely combines robust ambient stability with a direct ~ 1.5 eV band gap and a high Néel temperature of ~ 131 K. CrSBr therefore overcomes both the environmental and temperature constraints associated with earlier 2D magnets. This dissertation presents a comprehensive study of CrSBr, spanning from systematic characterization of its intrinsic properties to intentional tuning of its magnetic ground state via defect engineering. First, we characterize pristine CrSBr and clarify its intrinsic magnetism, resolving a long-debated anomaly around 40 K. Magnetization measurements on high-quality CrSBr crystals reveal no sign of the previously reported low-temperature phase transition, confirming that the A-type antiferromagnetic order is the only phase below the Néel temperature (TN ≈ 131 K). These findings indicate that the ~ 40 K magnetic anomaly observed in some studies originates from extrinsic effects. Building on this understanding, the dissertation then explores ion irradiation as a controlled means of tuning CrSBr’s magnetic ground state. By introducing an optimal density of defects through helium-ion bombardment, an interlayer ferromagnetic coupling is induced, resulting in a transition from the native antiferromagnetic state to a ferromagnetic state with a Curie temperature (TC) up to ~ 110 K. The induced ferromagnetic phase retains the crystal lattice and magnetic anisotropy of pristine CrSBr. Under moderate irradiation fluences, a “rise and fall” behavior is observed: the induced ferromagnetic coupling first strengthens with increasing defect density, then beyond an optimal point, the ferromagnetic order is progressively degraded. At higher irradiation levels, the induced long-range ferromagnetic order is fully suppressed and transition to paramagnetism accompanied by a structural phase transition, highlighting a threshold of disorder tolerance beyond which long-range magnetism collapses. Overall, these results demonstrate the ability to generate “ferromagnetism on demand” in an air-stable 2D magnet and establish defect engineering as a powerful strategy for tailoring magnetic properties. This dissertation bridges fundamental studies of 2D magnetism with pathways toward practical implementations in future spintronic and quantum technologies.
- Freie Schlagwörter (DE)
- 2D-Magnete, 2D-Halbleiter, Defekte, Ionenbestrahlung, Induzierter Ferromagnetismus
- Freie Schlagwörter (EN)
- 2D magnets, 2D semiconductor, Defects, Ion irradiation, Induced ferromagnetism
- Klassifikation (DDC)
- 538
- Klassifikation (RVK)
- UP 6300
- GutachterIn
- Prof. Dr. Artur Erbe
- Prof. Dr. Farsane Tabataba-Vakili
- Den akademischen Grad verleihende / prüfende Institution
- Technische Universität Dresden, Dresden
- Sonstige beteiligte Institution
- Helmholtz-Zentrum Dresden-Rossendorf, Dresden
- Version / Begutachtungsstatus
- publizierte Version / Verlagsversion
- URN Qucosa
- urn:nbn:de:bsz:14-qucosa2-1046323
- Veröffentlichungsdatum Qucosa
- 12.06.2026
- Dokumenttyp
- Dissertation
- Sprache des Dokumentes
- Englisch
- Lizenz / Rechtehinweis
CC BY-NC-ND 4.0- Inhaltsverzeichnis
1. Introduction 3 1.1 Two-dimensional (2D) magnetic materials 3 1.1.1 Categories of Magnetic Materials 3 1.1.2 The magnetic Exchange Interaction 4 1.1.3 Emergence and Significance of 2D Magnetic materials 5 1.2 CrSBr 7 1.2.1 Crystal structure 7 1.2.2 Electronic band structure 8 1.2.3 Magnetic properties 10 1.2.4 Electronic properties 12 1.2.5 Optical properties 15 1.3 External control of the magnetic properties of CrSBr 18 1.3.1 Strain-driven properties 18 1.3.2 Electrostatic doping-induced properties 19 1.3.3 Chemical doping-induced properties 21 1.3.4 Hetero-stacking induced properties 23 1.4 Hypothesis and organization of this thesis 25 1.5 Proposed Approach 28 1.5.1 Sample Preparation 29 1.5.2 Structural and Magnetic Characterization 29 2. Intrinsic magnetic properties of the layered antiferromagnet CrSBr 31 2.1 Introduction 32 2.2 Experiment 33 2.3 Results and Discussions 34 2.4 Conclusion 41 3 Ferromagnetic Interlayer coupling in CrSBr crystals Irradiated by Ions 42 3.1 Introduction 43 3.2 Experiment 44 3.3 Results and Discussions 47 3.4 Conclusion 61 4 Rise and Fall of the Ferromagnetism in CrSBr Flakes by Non-magnetic Ion Irradiation 62 4.1 Introduction 63 4.2 Experiment 64 4.3 Results and Discussions 65 4.4 Conclusion 72 5 The structural and magnetic phase transition in CrSBr with further increasing irradiation fluence 73 5.1 Introduction 73 5.2 Experiment 75 5.3 Results and Discussion 76 5.4 Conclusion 81 6 Summary and outlook 82 6.1 Summary 82 6.2 Outlook 83 Bibliography 86 Publication List (during PhD study) 93 Curriculum Vitae 95 Acknowledgement 97 Abbreviations & Acronmys 99