| Summary: | From density functional theory investigations helped with crystal chemistry rationale, single-atom C, embedded in layered hexagonal CC’<sub>n</sub> (<i>n</i> = 6, 12 and 18) networks, is stable in a magnetic state with M(C) = 2 μ<sub>B</sub>. The examined compositions, all inscribed within the P6/mmm space group are characterized as increasingly cohesive with n, figuring mono-, bi- and tri-layered honeycomb-like C’6 networks respectively. The spin projected total density of states shows a closely half-metallic behavior with a gap at minority spins (↓) and metallic majority spins (↑). Such results together with the large C-C intersite separation and the integer 2 μ<sub>B</sub> magnetization, let us propose an intra-band mechanism of magnetic moment onset on carbon 2<i>p</i> states. Support is provided from complementary calculations assuming a C<sub>2</sub>C’<sub>12</sub> structure with planar 2C with d(C-C) = 2.46 Å resulting into a lowering of the magnetization down to the 0.985 μ<sub>B</sub>/C atom and a ferromagnetic order arising from interband spin polarization on C where one nonbonding spin polarizes whereas the other is involved with the bonding with the other carbon. Illustration of proofs is provided with the magnetic charge density projected onto the different atoms, showing its prevalence around C, contrary to the C’<sub>n</sub> (C’6 layers), as well as electron localization function ELF.
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