Structural, electronic, and magnetic properties of MSi2N4 (M=Tm, Pa, Np) monolayers

Abstract Recently, a new two-dimensional (2D) MoSi 2 N 4 layered material was successfully synthesized [Science 369(2020)670], attracting significant attention from the research community. Following up on this work, we have successfully predicted other three stable MSi 2 N 4 (M=Tm, Pa, Np) monolayers in the 2D MA 2 Z 4 family using the CALYPSO structural prediction method combined with first-principles calculations. The energy band structure calculations show that the TmSi 2 N 4 monolayer is a ferromagnetic (FM) semimetal, and the PaSi 2 N 4 monolayer is a FM metal. In contrast, NpSi 2 N 4 monolayer is a FM semiconductor with Curie temperature of 812 K, which is higher than those of the vast majority of 2D FM semiconductor materials. The Curie temperature of NpSi 2 N 4 monolayer is attributed to the large magnetic moments of Np atoms and the strong exchange coupling interactions between the adjacent Np atoms. Interestingly, the Curie temperature of the NpSi 2 N 4 monolayer can be further enhanced through reasonable modulation of biaxial strain. It is about 1008 K under a biaxial tensile strain of 3%. The present findings deepen our understanding of the structural and magnetic properties of MSi 2 N 4 (M=Tm, Pa, Np) monolayers, and offer important insights for the design and synthesis of multifunctional nanoelectronic devices.