FERROMAGNETIC SEMICONDUCTOR

Toward intrinsic room-temperature ferromagnetism in two-dimensional semiconductors

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)

doi: 10.1088/1674-4926/40/8/080201