Multiple Spin State Analysis of Magnetic Nano Graphene

抄録

  Recent experiments have suggested a possibility of room-temperature ferromagnetism in graphite-like materials. We analyzed multiple spin states in asymmetric graphene molecules to find the mechanism responsible for ferromagnetism. First principle density functional theory was applied to calculate ground state spin density, energy, and atom position depending on each spin state. Molecules with dihydrogenated zigzag edges like C₆₄H₂₇, C₅₆H₂₄, C₆₄H₂₅, C₅₆H₂₂, and C₆₄H₂₃ indicated that the highest spin state in every molecule is the most stable having an energy difference of kT = 3000 K with the next spin state. In contrast, nitrogen substituted molecules like C₅₉N₅H₂₂, C₅₂N₄H₂₀, C₆₁N₃H₂₂, C₅₄N₂H₂₀, and C₆₃N₁H₂₂ demonstrated opposite results where the lowest spin state was the most stable. The magnetic stability of graphene molecules can be explained through three key factors depending on the edge specified localized spin state, the exchange interaction between parallel spins inside a molecule, and optimized atom position. We intend to apply these results to design carbon-based magnets, ultra high density information storage, and spintronic devices.