▎ 摘　　要

The lack of intrinsic spin polarization in graphene as well as in its several composites limits their usage as suitable spintronic material. Using long-range dispersion corrected density functional theory, we explore the structural, electronic, magnetic, and optical properties of recently synthesized [Liu, Q Zhang, J. Langmuir 2013, 29, 3821-3828] two-dimensional graphitic carbon nitride (g-C3N4) stacked graphene (C3N4@graphene) where 3d transition metals (TMs) are embedded in the cavity of g-C3N4 (TM-C3N4@ graphene). The incorporation of TMs modifies the structure of C3N4@graphene negligibly and keeps graphene almost as in its pristine form. TM inclusion makes the narrow-gap semiconducting C3N4@graphene as metallic. Charge-transfer analysis shows that the TM-C3N4 transfers electrons from the 3d-orbital of TM to the conduction band of graphene, making it n-doped in nature. Importantly, Cr, Fe, Co, and Ni embedded C3N4@graphene shows long-range ferromagnetic coupling among TMs in their ground state. The magnetic ordering appears due to suitable ferromagnetic d-p exchange interaction, which is absent in paramagnetic V- and Mn-C3N4@graphene sheets. Furthermore, calculated high charge carrier densities of the n-doped graphene layer in these nanocomposites are quite promising for its usage in ultrafast electronics. Performing Heisenberg model based Monte Carlo simulations, we predict the Curie temperatures for Cr- and Fe-C3N4@graphene as 381 and 428 K, respectively. Moreover, these sheets also demonstrate prominent visible light response, which gives us a clue about their probable photocatalytic activity. Thus, the present study exhibits the true multifunctional behavior of TM-C3N4@graphene by demonstrating its usage in various fields, such as memory devices, spintronics, ultrafast electronics, photocatalysis, etc.