Superhard bulk C 4 N 3 compounds with metal-free magnetism assembled from two-dimensional C 4 N 3 : a first-principles study.

Enriching the electronic properties of superhard materials is very important to extend their applications, and some superhard materials with metallic or superconducting characteristics have been designed via theoretical or experimental methods. However, their magnetic features have scarcely been studied, since most of them are limited to nonmagnetic ordering. Here, with the help of first-principles calculations, a series of C 4 N 3 compounds are designed by stacking C 4 N 3 sheets with different sequences. As expected, some of them exhibit both magnetic and superhard characteristics. Notably, all these compounds exhibit dynamic and mechanical stabilities, indicating that their dynamic and mechanical stabilities are independent of the stacking sequence. Among them, the ABC-stacked one is energetically favorable, and it exhibits antiferromagnetic ordering and has a hardness of ∼54.0 GPa, and the electronic calculations show that it is a semiconductor with a direct band gap of ∼1.20 eV. Besides, the magnetism of all magnetic C 4 N 3 compounds is caused by the lower coordinated atoms, and the magnetic moments are located on three-fold C or two-fold coordinated N atoms. Additionally, the magnetic property is deeply dependent on the external pressure. This work opens a potential way to design magnetic superhard materials and can arouse their applications in the spintronic field.