First-principles predictions of new superhard magnetic clathrate material β-C₃N₂ through atom embeddedness

Using first-principles calculations, we predict the coexistence of mechanical superhardness and the controllable magnetism in the clathrate material β-C₃N₂ through the implant of the external atom into the intrinsic cage structure. Taking hydrogen-doping (H@β-C₃N₂) and fluorine-doping (F@β-C₃N₂) as examples, our calculations indicate these two doped configurations are stable and discover that they belong to antiferromagnetic semiconductor and ferromagnetic semi-metal, respectively. These intriguing magnetic phase transitions originate from their distinctive band structures around the Fermi level and can be well understood by the three-dimensional Hubbard model with half-filling occupation and the Stoner model. Moreover, the high Vickers hardness of 49.0 GPa for H@β-C₃N₂ and 48.2 GPa for F@β-C₃N₂ are obtained, suggesting they are clathrate superhard materials as their host. Therefore, the incorporations of H and F in β-C₃N₂ give rise to new types of superhard antiferromagnetic semiconductor and superhard ferromagnetic semimetal, respectively, which could have potential applications in harsh conditions. Our work provides an effective strategy to design a new class of highly desirable multifunctional materials with excellent mechanical properties and magnetic properties, which may arouse spintronic applications in superhard materials in the future.