Structural, electronic and magnetic properties of 3d transition metals embedded graphene-like carbon nitride sheet: A DFT + U study

• TMs embed in the cavity of g-CN regularly and keep intact of the planar structure.
• There is Jahn–Teller distortion inevitably under hexagonal crystal field.
• Nonmagnetic and semiconducting g-CN can be modulated to be magnetic and metallic.
• Magnetic coupling between TMs varies dramatically with the change of distance.

Using first-principles calculations, we have investigated the structural, electronic and magnetic properties of 3d transition-metals (TMs) embedded two dimensional graphene-like carbon nitride sheet (TMs@g-CN). Our results show that TMs embed in the cavity of g-CN sheet regularly and keep intact of the planar structure, though there is Jahn–Teller distortion inevitably. Additionally, the nonmagnetic and semiconducting sheet can be significantly modulated to be magnetic and metallic behaviors induced by the resonant impurity states between TMs 3d and g-CN 2p orbitals. Moreover, we also explore the magnetic coupling of TMs@g-CN and find that it varies dramatically with the change of the distance between TMs, i.e., from ferromagnetic (FM) to antiferromagnetic (AFM) transition. Finally, the underlying physical mechanism of the above findings is discussed.