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

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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.