J. Am. Chem. Soc., 140, 11519–11525 (2018)
Two-dimensional (2D) ferromagnetic semiconductors have been recognized as the most promising candidates for next-generation low-cost, high-performance and nano-scale spintronic applications such as spin field-effect transistors and quantum computation/communication. However, as one of the 125 important scientific issues raised by Science journal in 2005 that “is it possible to create magnetic semiconductors that work at room temperature?”, how to achieve a feasible ferromagnetic semiconductor with high Curie temperature is still a long-standing challenge despite of tremendous efforts have been devoted in this field since 1960s. The recent discovery of 2D ferromagnetic semiconductors Cr2Ge2Te6 and CrI3 has evoked new research interests in 2D intrinsic ferromagnetic semiconductors. But the low Curie temperature (< 45 K) of these materials is still badly hindering their industrial applications.
Recently, a group led by Professor Erjun Kan and Professor Hongjun Xiang gives a clue to solve this problem. They proposed that, by using two isovalent transition metal ions to construct an alloy compound, an intrinsic ferromagnetic semiconductor with Curie temperature up to room-temperature may be achieved. This chemical approach is based on a solid physical mechanism that, the superexchange interactions between adjacent magnetic ions could be enhanced by an on-site energy level staggering of d orbtials, as demonstrated by a simple double-orbital model. Because the exchange fields of different transition metal ions are usually different, the isovalent alloying may result in a large energy level staggering of d orbitals, leading to a significant enhancement of ferromagnetic couplings. They further used first-principles calculation methods to predict several double-metal ferromagnetic semiconductors, whose Curie temperatures are improved by 3–5 times in comparison with the single-metal basis materials. This work has revealed a new physical mechanism of enhancing ferromagnetic coupling in semiconductors without introducing any impurities or carriers and demonstrated the possibility of room-temperature ferromagnetic order in 2D semiconductors.
Fanlong Ning (Zhejiang University, Hanzhou, China)