Theoretical and experimental progress of two-dimensional ferromagnetic semiconductors

In the era of big data, the demand for non-volatile and efficient storage and processing of massive electronic information has promoted the rapid development of electronic information technology. As the core material of transistors, semiconductor materials are widely used in various electronic devices. However, due to the increasingly significant "heat dissipation" and "quantum tunneling" effect of traditional semiconductor devices at the nanoscale, it is difficult to meet people's demand for more miniaturized electronic information equipment. Therefore, it is urgent to develop new functional semiconductor materials. The appearance of magnetoresistance information storage technology makes people pay more attention to the magnetic properties of devices. At the same time, spintronics, which is a new discipline, is developed to study the correlation between electron charges and spin properties. As the core material of new functional spintronic devices, ferromagnetic semiconductors have attracted wide attention due to their unique magnetoelectric properties. In recent years, the discovery of two-dimensional ferromagnetic materials has opened a new stage for the development of ferromagnetic semiconductors. However, according to Mermin-Wagner's theory, due to the strong thermal fluctuations in two-dimensional materials at finite temperatures, a two-dimensional system with long-range magnetic order has been thought to be non-existent. It is found that the effect of thermal fluctuation on magnetic order can be offset by the magnetic anisotropy of the system. Moreover, it is found that there is an inherent long-range magnetic order in the two-dimensional CrGeTe3 and CrI3 structures. This provides a platform for the research of two-dimensional magnetic semiconductors. In this review, we focus on the room temperature magnetic order stability of two-dimensional ferromagnetic semiconductors, taking CrGeTe3, CrI3, and other typical two-dimensional magnetic semiconductors as examples, to introduce the recent experimental progress of two-dimensional ferromagnetic semiconductors. At the same time, in the theoretical research, this paper introduces the two-dimensional magnetic semiconductors and their magnetic properties discovered by structural search and design in recent years. The existing two-dimensional magnetic semiconductor is modified by surface adsorption, charge doping and stress application. Based on the two-orbit model based on the tightly bound approximation, the Curie temperature can be increased by enhancing the ferromagnetic exchange interaction and weakening the antiferromagnetic exchange interaction, and the significance of magnetic anisotropy is discussed. Finally, we briefly prospect the future development of two-dimensional ferromagnetic semiconductors from two aspects of p electron magnetism and low energy consumption electronic magnetic control. It is hoped that this review will enlighten people to understand two-dimensional ferromagnetic semiconductors and magnetic coupling mechanism comprehensively.