Since the discovery of graphene in 2004, research on two-dimensional materials has entered the field of scientists' vision. So far, researchers have discovered at least dozens of two-dimensional materials with completely different properties, including insulators, semiconductors, metals, and more. Recently, Professor Zhang Yuanbo's team from the Department of Physics at Fudan University made a significant breakthrough in the field of two-dimensional magnetic materials - discovering a new type of magnetic two-dimensional material Fe3GeTe2, providing a new ideal system for studying two-dimensional itinerant magnetism. In addition, through lithium-ion intercalation regulation, the research team has achieved a ferromagnetic transition temperature above room temperature in Fe3GeTe2 thin layers, providing new possibilities for the development of ultra-high density, gate voltage adjustable, and room temperature usable magneto electronic devices based on this material in the future.

On October 22nd (London time), the study titled "Room Temperature Ferromagnetism Controlled by Gate Voltage in Two Dimensional Iron Germanium Tellurium" was conducted

（“Gate-tunable Room-temperature Ferromagnetism in Two-dimensional Fe3GeTe2”） The title was published in the academic journal Nature. Professor Zhang Yuanbo from the Department of Physics at Fudan University is the corresponding author of the paper, while Deng Yujun, a doctoral student from the Department of Physics in 2016, and Yu Yijun, a postdoctoral fellow, are co authors of the paper.

With the successful separation of graphene, a single atomic layer graphite material, the concept of two-dimensional materials was officially proposed. Graphene is a thin sheet composed of only one layer of carbon atoms. As a two-dimensional material, graphene corresponds to graphite as its parent material, which is a layered material formed by stacking two-dimensional materials through interlayer van der Waals interactions. Since the 1970s, layered materials have attracted considerable attention due to research in fields such as charge density waves, superconductivity, and lithium batteries. Preparing small units in layered materials - a single layer - for research is like opening a book and carefully reading a page. In depth research on two-dimensional materials may not only help us unravel the mysteries of these layered parent materials, but also lead us to discover physics hidden within them that do not exist in three-dimensional systems. More importantly, all atoms in two-dimensional materials are exposed on the surface, and the parts of the "body" that are not hidden are easier to manipulate compared to three-dimensional materials

In recent years, magnetic two-dimensional materials have become a new research hotspot. In the relevant research of Zuixin, researchers used insulating layered magnetic materials Cr2Ge2Te6 and CrI3 as the research objects, and detected the two-dimensional magnetism in the materials using optical means. But these materials are all insulating, and the ferromagnetic transition temperature is much lower than room temperature, which poses great obstacles in the preparation and application of electronic devices.

On the basis of previous research, Zhang Yuanbo's team used metallic layered materials as the research object. After two years of exploration and a year of continuous experiments, they finally obtained a new type of two-dimensional magnetic material Fe3GeTe2. Zhang Yuanbo's team found through experiments that single-layer Fe3GeTe2 still exhibits ferromagnetic long program and out of plane magnetic anisotropy at low temperatures. More importantly, Zhang Yuanbo's team utilized their own developed technology to intercalate Fe3GeTe2 thin layers with lithium ions, raising the ferromagnetic transition temperature of the sample above room temperature, providing the possibility for future electronic device fabrication using this material.

A new approach: a novel sample cleavage method　　

In the field of two-dimensional materials, the traditional tape cleavage method is a commonly used way to prepare single-layer materials by cleaving layered materials. The tape cleavage method, which has been used in academia for over a decade, is very effective but also very simple and primitive, with unavoidable defects. There are few materials that can be cleaved using this method, and the cleavage ability is limited. For research teams, breaking through traditional methods and exploring new paths is the only way to obtain the monolayer of two-dimensional magnetic materials they are studying, and even further expanding to many other unknown two-dimensional materials.

After difficult exploration and continuous experimentation, Zhang Yuanbo's team finally developed a new sample cleavage method - using the strong adhesion and large contact area between alumina and Fe3GeTe2 to prepare single-layer samples. This method has high preparation efficiency and strong cleavage ability, and will also provide new methods and research ideas for effective cleavage of other layered materials similar to Fe3GeTe2 cleavage difficulty. It is the discovery of new cleavage methods that enables research teams to further investigate the electrical transport properties of this magnetic two-dimensional material.

Image caption: a: Atomic structure of single-layer Fe3GeTe2. b: Schematic diagram of a new mechanical cleavage method using alumina. c: The phase diagram of Fe3GeTe2 with respect to thickness and temperature. d: Room temperature magnetism of Fe3GeTe2 thin layer.

According to Zhang Yuanbo, the newly discovered magnetic two-dimensional material Fe3GeTe2 in this study will provide a possibility for scientists to develop ultra-high density, gate voltage adjustable, and room temperature usable magnetic electronic devices based on this material in the future. The newly discovered two-dimensional material cleavage method will expand new ideas for the research of two-dimensional materials in the future.

Basic research is not application-oriented, but exploring various possibilities. New materials and new physical properties are the starting point of our research, "said Zhang Yuanbo. For the research team, there are still more possibilities waiting for them to discover and explore in the future.