On the other hand, silicon has a suitable energy level gap, good carrier mobility, and the most abundant reserves in the earth, thus becoming the basis of the modern semiconductor industry, and is the material of choice for the next generation of micro-nanoelectronic devices. At present, silicon is mainly used to control logic information by the degree of freedom of conductance formed by its charge in various devices. However, as the feature size of the device continues to evolve toward the micro-nano scale, this manipulation is encountering bottlenecks in integration and energy consumption. Exploring the use of silicon's spin freedom to achieve the integration of logic and storage, reducing device energy consumption, is widely recognized as one of the important ways to solve this problem. Numerous studies have focused on the generation of spin polarization in silicon materials, but the spin polarization that creates internal enthalpy in silicon structures remains challenging.








Controlling the magnetic properties of silicon by strain and carrier concentration


In response to the above two problems, the team of Nanostructured Institute of Mechanical Structural Mechanics of Nanjing University of Aeronautics and Astronautics discovered that the magnetic graphene nanoribbons placed on the silicon substrate have a two-stage linear magnetoelectric effect with bias modulation (PRL 103, 187204, 2009). Recently, the team followed the research idea of the low-dimensional structure's peculiar force-electro-magnetic coupling effect, using the first-principles calculation of the system to find that the most common Si(001) surface can be on the silicon surface under the action of the gate voltage. Spin magnetism is spontaneously formed, and the local spin magnetic moment tends to be ferromagnetically coupled. The surface magnetism originates from the localized electronic state caused by the surface reconstruction of the silicon, which generates an electron-electron interaction under charge doping and undergoes exchange splitting. Further research has found that the use of strained silicon technology can further enhance the ferromagnetism of the silicon surface and form the electrical transport properties of semimetals that conduct only a single spin channel.








Ferroelectric reversal and magnetoelectric coupling of silicon surface








At the same time, the team found that the silicon dimer on the Si(001) surface has spontaneous polarization due to symmetry destruction, and the overall performance has strong antiferroelectricity even under the action of hole doping. This makes the above ferromagnetism and antiferroelectricity rarely coexist on the surface of the silicon containing hole carriers. More interestingly, under the action of the external electric field, the dimer of the silicon surface is reversed by the electrostatic force, so that the surface reconstruction of the silicon is rearranged along the direction of the electric field to form a ground state with ferroelectricity. . At the same time as the antiferroelectric-ferroelectric transition, the entire silicon surface changes from ferromagnetic to non-magnetic, demonstrating that the silicon surface containing hole carriers has mutually coupled electrical and magnetic sequences, for the first time in the absence of metallic elements. Multiferroic properties are achieved on pure silicon surfaces. In addition, the use of strained silicon technology or increased carrier concentration can significantly reduce the electric field strength required to drive the antiferroelectric-ferroelectric transition on the silicon surface, revealing the unique force-electro-magnetic coupling effect of the silicon surface.


This work provides a scientific basis and possible technical approach for the development of silicon-based magnetoelectric devices.