Recently, the High Magnetic Field Science Center of the Hefei Institute of Physical Science, Chinese Academy of Sciences cooperated with researchers from the Institute of Solid State Physics to carry out a series of research on two-dimensional ferromagnetic/antiferromagnetic materials. Magnetic carbon nanosheets) and two-dimensional magnetic material type development (two-dimensional organic antiferromagnetic polymers) progress. Relevant results were published in the journals of C and ( ) respectively.
Magnetic materials are the basis of spintronic devices. The research and development of two-dimensional magnetic materials provides the possibility to realize spintronic devices with smaller size and lower energy consumption in the future, so it has become a new favorite in the field of material physics. At present, there are two aspects of research in this field that have attracted much attention: one is to increase the Curie temperature of the two-dimensional system, preferably above room temperature; the other is to broaden the types of two-dimensional magnetic materials. In addition to inorganic materials, organic materials are also needed. Yes, in addition to ferromagnetic ones need antiferromagnetic ones.
Figure 1: Schematic diagram of room temperature ferromagnetic carbon nanosheets induced by zigzag boundaries
Figure 2: Coverage and magnetic data of 2D antiferromagnetic multi-radical nanosheets
Currently, most 2D magnetism is achieved by mechanically exfoliating 3D magnetic crystals. The intrinsic Curie temperature of such systems is usually very low (< 250 K). To increase the Curie temperature, in addition to element doping and external field regulation, defect engineering is also one of the important options. Theory and experiments have proved that strong magnetic coupling can also be established between sp2 electrons in non-metallic and light element systems, and it is possible to achieve a transition temperature above room temperature. Therefore, it is also promising to introduce magnetism through defect engineering (doping, adsorption, point defects, edges, free radicals, etc.) on originally nonmagnetic 2D materials, and this external magnetism is expected to achieve higher transition temperatures. .
Through cooperative research, the project team used the Woods reaction to synthesize amorphous carbon nanosheets embedded with graphite nanocrystals, and found that the ferromagnetic intensity at room temperature caused by the zigzag boundary (edge) of graphite nanocrystals can reach 0./g, which is higher than before. high. It has been reported that the room-temperature ferromagnetism of graphite induced by point defects is two orders of magnitude larger. Combining further experiments and first-principles calculations, the researchers found that the magnetic properties of carbon nanosheets mainly depend on the distance between the zigzag boundaries. As the distance decreases from 3.6 nm to 0.8 nm, the magnetic coupling between the boundaries changes from ferromagnetic to antiferromagnetic. Room temperature ferromagnetism is a prerequisite for the application of two-dimensional magnetic materials. These findings provide feasibility for the application of carbon-based magnetic materials.
On the other hand, behind the extensive research on inorganic 2D magnetic materials, the preparation of 2D organic magnetic materials still faces challenges. So far, only one 2D organic ferromagnetic material has been discovered, and 2D organic materials with antiferromagnetic behavior remain to be developed. The project team first designed and synthesized three (2,3,5,6-tetrachloro-4-ethynylphenyl) methyl radicals as monomers, and then prepared free-standing Two-dimensional organic magnetic multiradical (OMP) nanosheets. Through the magnetic exchange coupling between radicals, the obtained 2D OMP nanosheets have antiferromagnetic properties, and the Neel temperature reaches 42.5K. To the best of our knowledge, this is the first demonstration of a novel 2D organic structured man-made material with antiferromagnetic properties as a fundamental building block for 2D organic spintronic devices. This work was chosen as the cover of this issue.
The above research work has been supported by the National Natural Science Foundation of China, the National Key Research and Development Program, and the Key Research Project of Frontier Science of the Chinese Academy of Sciences.