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重点是研究Cr2Ge2Te6（一种被称为铁磁绝缘体（FMI）的材料）的磁性随厚度的变化。Cr2Ge2Te6在凝聚态物理中很有趣，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用Cr2Ge2Te6晶体，并将其剥离，直到我们有一组具有不同厚度的几个单位细胞的样品。接下来，将使用一种称为微霍尔磁法的技术来研究样品的磁性。通过研究样品的磁性，可以得到永磁体强度随厚度变化的信息。如果时间允许，小片的Cr2Ge2Te6将与具有类似晶体结构的另一种材料（拓扑绝缘体）结合在一起。测量三明治结构的性质可以提供关于电子在两种材料界面上的行为的信息。铁磁绝缘体和拓扑绝缘体之间的这种界面可能会产生新的物理现象，如量子反常霍尔效应。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。本项目涉及铁磁绝缘体（FMI） Cr2Ge2Te6超薄层的磁性研究。物理研究所的李永清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的变化。由于超薄样品体积小，因此将使用微霍尔磁强计和表面敏感微克尔显微镜测量其磁性能。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超薄Cr2Ge2Te6集成到拓扑绝缘体（TI）上。PI还将对FMI/TI混合结构进行初始磁输运测量。该奖项隶属于东亚和太平洋暑期研究所项目，由美国国家科学基金会和中国科技部共同资助，支持美国研究生的暑期研究。

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.