Void-Defect Induced Magnetism and Structure Change of Carbon Materials -Ⅰ: Graphene Nano Ribbon

Abstract

Void-defect is a possible origin of ferromagnetic-like feature of pure carbon material. Applying density functional theory to void-defect induced graphene-nano-ribbon (GNR), a detailed relationship between multiple-spin-state and structure change was studied. An equilateral triangle of an initial void having six electrons is distorted to isosceles triangle by re-bonding carbon atoms. Among possible spin-states of Sz=0/2, 2/2, 4/2 and 6/2, the most stable state was Sz=2/2. The case of Sz=4/2 is remarkable that initial flat ribbon turned to three dimensionally curled one having highly polarized spin configuration at ribbon edges. Total energy of Sz=4/2 was very close to that of Sz=2/2, which suggests coexistence of flat ribbon and curled ribbon. As a model of three dimensional graphite, bi-layered AB stacked GNR was analyzed for cases of different void position of α-site and β-site. Spin distribution was limited to the surface layer, nothing to the back layer. Distorted void triangle show 60degree clockwise rotation from αto β-site, which was consistent with experimental observation using the scanning tunneling microscope. This study revealed that void-defect in GNR induces unusual polarized spin state, different with usual ferromagnetic one. [ To be published on Journal of the Magnetics Society of Japan (2021), e-mail to Norio Ota: n-otajitaku@nifty.com ]