Graphitic-nitrogen-enhanced ferromagnetic couplings in nitrogen-doped graphene

Nitrogen doping is a promising approach to induce the basal-plane localized magnetic moments in $\mathit{sp}$-electron-only graphene sheets. Enhancing the magnetic couplings among the moments can contribute to the high Curie temperature ${T}_{C}$ and large ratio of ferromagnetism (FM), which is vital for real applications in spintronic devices; however, it is still challenging. Here, we experimentally demonstrate that graphitic nitrogen (N-Q) could enhance the ferromagnetic couplings of localized magnetic moments provided by the defective N in nitrogen-doped graphene (NG). Nearly pure FM at 2 K is obtained in ${\mathrm{NG}}_{16.04}$ (N-Q/N = 16.04 at. %) with a ${T}_{C}$ up to 397.5 K, while the room-temperature saturated magnetization is high as $\ensuremath{\sim}0.4$ emu/g. The rich $\mathrm{C}\ensuremath{\rightarrow}\mathrm{N}$ electrons contributed by the high ratio of the N-Q complex dominantly devote itinerant magnetism and enhance the interactions among the pyrrolic N (N-5) and/or pyridinic N complexes. Our density functional theory simulation results provide the configurations of (trimerized N-5)-triazinic N-Q along certain directions with enhanced sublattice-independent FM, which are proposed to be the magnetic structures in ${\mathrm{NG}}_{16.04}$. Our investigation reveals that introducing the N-Q can serve as an ideal route for the long-range spin correlations and thus full ferromagnetic couplings in graphene.