Ferromagnetism Triggered By N-defect Complexes In Graphitic Carbon Nitride

Recently,the realization of long-range ferromagnetic order in two-dimensional van der Waals crystals leads to the advancement of the spintronics,but the absence of intrinsic magnetism limits the applications of graphene in spintronics.It remains a challenge to induce robust long-range ferromagnetism in the graphene.A number of factors,e.g.atomic vacancies,functionalization of hydrogen?oxygen?atoms,and nitrogen doping,could induce localized magnetic moments.However,orderly magnetism can only be generated if long-range exchange coupling is formed between the induced local magnetic moments.In these strategies for exploring the magnetism of graphene,the substitutional N-doped graphene attracts much attentions as it exhibits robust ferromagnetism.Studies have shown that the concentration,configuration and magnetic interaction of N-defect complexes can affect the magnetism of graphene,and there is still some ambiguity and even controversy.It has been generally recognized that doping nitrogen in high concentration is considered as an important factor for graphene-like structures to induce long-range magnetic order.The trimerized pyridine?TPY?,graphitic N?GN?and graphitic 3N?G3N?are prevalent N-defect complexes,and can get up to high concentration.At low concentrations,their effects on the local magnetic moment of graphene have been widely studied,but their effects on the long-range magnetic order are still insufficient in graphene with high nitrogen concentration.In this paper,based on a variety of N-defect complexes such as TPY,GN and G3N,three new graphitic carbon nitride structures with energetic stability in chemical formula of C₁₀N₆,C₉N₇ and C₇N₉ are proposed by using the RG² code.We systematically assess the stability,electronic and magnetic properties based on first-principles calculations.The results show that both C₁₀N₆ and C₉N₇ are half metals,while C₇N₉ is a spin-polarized metal.The itinerant p electrons occupy the spin-polarized narrow bands near the Fermi level,which induces Stoner ferromagnetism in the C₁₀N₆ and C₉N₇.The direct exchange between the delocalized magnetic moment of the itinerant?electrons is responsible for the ferromagnetism in the C₇N₉.The magnetic moment is determined by both spin-polarized electronic structures and long-range magnetic interaction which depends on various factors such as the configuration and separation of N-defect complexes.In the C₁₀N₆ the interaction of D-TPYs induces ferromagnetism of 2.00?_B magnetic moment with both?and?components,while the interaction between TPY and GN?G3N?quenches?decreases?the?component of magnetic moment in the C₉N₇?C₇N₉?.Intriguingly,besides the magnetic interactions between the itinerant?electrons,we also find the direct magnetic interaction between localized in-plane unpaired electrons.Our results will assist to the exploration of magnetism for graphene-like,hoping to motivate experimenters to generate long-range magnetism in graphene-like materials.