| 中文题名： | 二维范德华材料磁性调控的理论研究 |
| 姓名： | |
| 保密级别： | 公开 |
| 论文语种： | 中文 |
| 学科代码： | 070205 |
| 学科专业： | |
| 学生类型： | 硕士 |
| 学位： | 理学硕士 |
| 学位类型： | |
| 学位年度： | 2022 |
| 校区： | |
| 学院： | |
| 第一导师姓名： | |
| 第一导师单位： | |
| 提交日期： | 2022-06-13 |
| 答辩日期： | 2022-06-01 |
| 外文题名： | Tunable magnetic properties of two-dimensional van der Waals |
| 中文关键词： | |
| 外文关键词： | Two dimensional van der Waals materials ; Heisenberg exchange coefficients ; Spin waves ; Charge transfer ; Coercivity ; Anisotropy energy |
| 中文摘要： |
单层二维磁性范德华材料CrI3的发现为研究原子尺度薄磁体的基本物理性质和高集成度磁性器件提供了理想的材料平台。研究表明应变可以极大地改变自旋交换作用，调控平面内、外反铁磁和平面内铁磁之间的相变，使单层CrI3显示出丰富的磁相图。但是应变是否会对材料的磁激发有影响还尚不清楚。除了发挥单个二维材料的性能，范德华异质结构能够将各个材料的优越性能结合起来，实现不同的功能。电荷转移在异质结构的界面上起着关键作用，它会影响材料的电子结构，最终影响材料的物理性质。然而，一旦界面形成，电荷转移就很难在外部进行控制。本文基于第一性原理的密度泛函理论主要对二维材料的磁性调控进行了研究，主要包含以下两个工作：
通过第一性原理计算确定了双轴应变下单层CrI3的海森堡交换作用系数，我们发现只有把Cr原子最近邻、次近邻、第三近邻交换作用都考虑进来时，才能较为准确地描述海森堡交换作用系数，并分析了其中直接交换与超交换的贡献。在此基础上，我们发现并讨论了CrI3的自旋激发随应变的变化，展示了应变对单层CrI3的磁基态及磁激发的调控作用，我们的结果对研究CrI3的自旋波行为有重要的参考价值。 |
| 外文摘要： |
The discovery of the single-layer two-dimensional magnetic van der Waals material CrI3 provides an ideal material platform for studying the fundamental physical properties of atomically thin magnets and highly integrated magnetic devices. The study shows that strain can greatly change the spin-exchange interaction, regulating the phase transition between in-plane, out-of-plane antiferromagnetism, and in-plane ferromagnetism,
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enabling monolayer CrI3 to display a rich magnetic phase diagram. But whether strain has an effect on the magnetic excitation of the material is unclear. In addition to exploiting the properties of a single two-dimensional material, van der Waals heterostructures can combine the superior properties of individual materials to achieve different functions. Charge transfer plays a key role at the interface of the heterostructure, which affects the electronic structure of the material and ultimately the physical properties of the material. However, once the interface is formed, the charge transfer is difficult to control externally. In this paper, the first-principles-based density functional theory mainly studies the magnetic regulation of two-dimensional materials, mainly including the following two works: The Heisenberg exchange coefficient of monolayer CrI3 under biaxial strain was determined by first-principles calculations. We found that only when the nearest-neighbor, second-neighbor, and third-neighbor exchange interactions of Cr atoms are taken into account, it can be described more accurately Heisenberg exchange interaction coefficient, and analyzed the contribution of direct exchange and superexchange. On this basis, we found and discussed the variation of the spin excitation of CrI3 with strain, and demonstrated the regulation of the magnetic ground state and magnetic excitation of monolayer CrI3. Our results are important for the study of the spin wave behavior of CrI3 reference value. Through first-principles calculations we report electrically controllable charge transfer in Fe3GeTe2/Cr2Ge2Te6/Fe3GeTe2 all-magnetic van der Waals heterostructures, which can be exploited to selectively modify the magnetic properties of the top or bottom Fe3GeTe2 electrodes. The directional charge transfer from metallic Fe3GeTe2 to semiconducting Cr2Ge2Te6 remarkably modifies magnetic anisotropy energy of Fe3GeTe2, leading to the dramatically suppressed coercivity. This study demonstrates a new approach to electronically control the magnetism of Fe3GeTe2, paving the way for the emergence of spintronic devices based on van der Waals magnets. |
| 参考文献总数： | 83 |
| 馆藏号： | 硕070205/22018 |
| 开放日期： | 2023-06-13 |
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