EAPSI: Thickness Dependence of the Magnetic Properties of the Ferromagnetic Insulator Cr2Ge2Te6

该奖项支持的研究和教育活动侧重于研究Cr2 Ge 2 Te 6（一种称为铁磁绝缘体（FMI）的材料）中磁性随厚度变化的演变。 Cr2 Ge 2 Te 6在凝聚态物理学中很有趣，因为它是少数既具有铁磁性又具有绝缘体的材料之一。该项目的第一部分将采取Cr2 Ge 2 Te 6晶体，并剥离它们，直到我们有一组具有不同厚度的几个晶胞的样品。 接下来，将使用称为微霍尔磁力测量的技术研究样品的磁性。 通过研究样品的磁性，可以获得关于永磁体的强度如何随厚度演变的信息。 如果时间允许，Cr2 Ge 2 Te 6的小薄片将与另一种具有类似晶体结构的拓扑绝缘体材料结合在一起。 测量夹层结构的特性可以提供有关电子在两种材料界面处如何行为的信息。 铁磁绝缘体和拓扑绝缘体之间的这种界面可能存在诸如量子反常霍尔效应之类的新物理现象。本项目将在中国科学院物理研究所李永清教授的指导下进行，该项目涉及铁磁绝缘体（FMI）Cr2 Ge 2 Te 6的磁性层的研究。 物理研究所的Yongqing Li教授已经获得了这种材料的高质量单晶，这种材料是一种层状铁磁绝缘体，可以剥离到几个原子层的厚度。一个近期目标是研究磁性随厚度变化的演化。由于样品体积小，磁性将用微霍尔磁强计和表面敏感微克尔显微镜测量。 在对FMI的磁性有了很好的了解之后，研究小组将探索将剥离的Cr2 Ge 2 Te 6集成到拓扑绝缘体（TI）上。 PI还将对混合FMI/TI结构进行初始磁输运测量。 该奖项属于东亚和太平洋夏季研究所计划，支持美国研究生的夏季研究，由NSF和中国科技部共同资助。

The research and education activities supported by this award focus on studying the evolution of magnetism as a function of thickness in Cr2Ge2Te6, a type of material known as a ferromagnetic insulator (FMI). Cr2Ge2Te6 is interesting in condensed matter physics because it is one of only a small number of materials that is both ferromagnetic and an insulator. The first part of the project will take crystals of Cr2Ge2Te6, , and exfoliate them down until we have a set of samples with varying thicknesses of a few unit cells. Next, the magnetic properties of the samples will be studied using a technique known as micro-Hall magnetrometry. By studying the magnetic properties of the samples, one can obtain information about how the strength of the permanent magnet evolves with thickness. If time permits, small flakes of Cr2Ge2Te6 will be combined in a sandwich with another material, a topological insulator, of similar crystal structure. Measuring the properties of the sandwich structure can provide information about how the electrons behave at the interface of the two materials. Such an interface between a ferromagnetic insulator and a topological insulator may host novel physical phenomena such as the quantum anomalous Hall effect. This project will be conducted under the mentorship of Professor Yongqing Li at the Institute of Physics, Chinese Academy of Sciences.This projects involves a study of the magnetic properties of ultrathin layers of the ferromagnetic insulator (FMI) Cr2Ge2Te6. Professor Yongqing Li at the Institute of Physics has obtained high quality single crystals of this material, which is a layered ferromagnetic insulator that can be exfoliated down to few atomic layers in thickness. One near term goal is to study the evolution of the magnetism as a function of thickness. Because of the small volumes of the ultrathin specimens, the magnetic properties will be measured with micro-Hall magnetometry and surface-sensitive micro-Kerr microscopy. After gaining good understanding of the magnetic properties of the FMI, the team will explore integrating the exfoliated ultrathin Cr2Ge2Te6 onto a topological insulator (TI). The PI will also perform initial magnetotransport measurements on the hybrid FMI/TI structure. This award under the East Asia and Pacific Summer Institutes program supports summer research by a U.S. graduate student and is jointly funded by NSF and the Ministry of Science and Technology of China.