Electronic and magnetic properties of diiron in extended carbon networks Fe2C6 and Fe2C12 from first principles

From density functional DFT investigations helped with crystal chemistry rationale, diiron (pairs of Fe), mostly known in molecular diiron nona-carbonyl Fe2(CO)9 and diiron-mono-carbide Fe2C carbide, are embedded in hexagonal C6 substructures. Generated Fe2C6 and Fe2C12 are shown to be more cohesive than the mono-carbide on one hand, and increasingly cohesive from hexa- C6 to dodeca- C12 on the other hand. From energy differences, the ground state is spin-polarized SP, versus a non-spin-polarized NSP configuration, and identified as ferromagnetic versus a higher energy anti-ferromagnetic hypothesis. The projection of the magnetic charge density on Fe and C, shows that only Fe carries the magnetic moment, while carbon receives charges from Fe as illustrated by the electron localization function ELF 3D and 2D mapping. SP configuration induces an enlarged c/a hexagonal ratio, versus NSP, while a(hex.) remains constant thanks to the rigid C6 carbon substructure network, resulting in an anisotropic magneto-volume response. This feature, essentially due to in-plane diiron, is discussed from the energy-volume (E, V) NSP and SP equations of state EOS and derived quantities like volume- and d(Fe-Fe)- changes of the magnetization.
Comment: 18 pages, 1 Table, 5 Figures