- 學位論文
缺陷和介面在二維磁性凡德瓦異質結構中的作用
The role of defects and interface in 2D magnetic van der Waals heterostructures
摘要
自從2017年二維磁性在單層三碘化鉻(CrI3)和碲化鉻鍺(CrGeTe3)中被觀察到後，二維凡德瓦磁性系統由於其在基礎物理中的重要性和低功耗器件中的潛在應用，受到了廣泛的研究。特別是，含有二維磁性材料的凡德瓦異質結構為通過介面效應來操縱二維磁性的研究提供了一個新的平台。三碘化鉻因其有趣的層數相關和堆疊相關磁性現象而成為最被廣泛研究的二維凡德瓦磁性材料。在此論文中，我們使用第一性原理計算研究了由三碘化鉻和二維過渡金屬二硫族化物組成的凡德瓦異質結構中的層間磁耦合。在第三章中，我們發現儘管AB堆疊的雙層三碘化鉻表現出層間鐵磁耦合，但在三碘化鉻/二碲化鉬(MoTe2)/三碘化鉻三層結構中，兩層三碘化鉻之間的層間磁耦合變成了反鐵磁。由於凡德瓦異質結構中的層間磁耦合主要由超交換作用機制主導，我們基於超交換作用理論對這一結果進行了討論。我們將層間耦合的變化歸因於超交換路徑的改變。在第四章中，我們研究了三碘化鉻的固有磁性與二硒化鉬(MoSe2)和二硒化鉑(PtSe2)中的缺陷誘導磁性之間的層間磁耦合。我們的結果顯示，過渡金屬空缺誘導的磁矩與相鄰的鐵磁性三碘化鉻之間的層間磁耦合是鐵磁耦合。在最後一部分，受北京理工大學吳漢春教授的實驗結果啟發，我們探討了二硒化錸(ReSe2)/石墨烯中皺摺結構誘導磁性和缺陷誘導磁性的可能性。我們發現，單靠皺摺不能解釋在二硒化錸/石墨烯異質結構中觀察到的磁響應。
並列摘要
Since the discovery of 2D magnetism in monolayer CrI3 and CrGeTe3 in 2017, 2D van der Waals (vdW) magnetic systems have been intensively studied because of their importance in fundamental physics and prospective applications in low-power devices. In particular, vdW heterostructures containing 2D magnetic materials have offered a new platform for studying the manipulation of 2D magnetism via interfacial effect. Chromium triiodide (CrI3) is the most intensively studied 2D vdW magnetic material for its interesting layer-dependent and stacking-dependent magnetism. In this dissertation, we investigate the interlayer magnetic coupling in vdW heterostructures composed of CrI3 and 2D transition metal dichalcogenides (TMDs) using first principle calculation. In Chapter 3, we found that while the AB stacking bilayer CrI3 exhibits interlayer ferromagnetic coupling, the interlayer magnetic coupling between two layers of CrI3 becomes antiferromagnetic in the CrI3/MoTe2/CrI3 trilayer structure. Since the interlayer magnetic coupling in vdW heterostructures is dominated by the superexchange mechanism, this result is discussed based on superexchange theory. We attribute the change of interlayer coupling to the modification of superexchange path. In Chapter 4, we investigate the interlayer magnetic coupling between intrinsic magnetism in CrI3 and defect-induced magnetism in molybdenum diselenide (MoSe2) and Platinum diselenide (PtSe2). Our result shows that the transition metal vacancy-induced magnetic moments couple ferromagnetically to the adjacent ferromagnetic CrI3. In the last part, motivated by the experimental results of our collaborator, Prof. Han-Chun Wu at the Beijing Institute of Technology, we explore the possibilities of wrinkle structure induced magnetism and defect-induced magnetism in ReSe2/graphene. We found that wrinkles alone cannot account for the observed magnetic response in ReSe2/graphene heterostructure.