Halfmetal and SGS in armchair BNC nanoribbons Z
Half-metal and SGS in armchair BNC nanoribbons Z. M. Liu( 刘宗民) and Z. Q. Yang(杨中芹) Phys. Dept. , Fudan Univ. , Shanghai, People’s Republic of China Introduction : We perform first-principles calculations based on density functional theory to study electronic and magnetic properties of armchair BNC nanoribbons. We find armchair BNC nanoribbons present half-metal (HM) with 1. 0 u. B in the systems where N do not pair to B in the unit cell. The C atoms at the edges are mainly responsible for the local magnetic moment. Especially, for the nanoribbons with the both edges composed by CNCC and BNCC atoms transform to spin gapless semiconductors (SGS) from HM where both edges saturated with H. The reason is that H is compete to the atoms at one edge that mainly contribute to the band near fermi level at X poin make the spin band near fermi level. Method: Ab initio calculations within density functional theory (DFT). (a) A: Systems with unpaired N atoms (b) (a) 9 -CCCC-NCCB (b) 10 -CCCC-CCBN (c) 11 -CCCC-CBNC Model: , FIG. 1. Schematic illustrations of two typical armchair BCN nanoribbons : 13 -CNCC(a) , 13 CCCC-CCCC (b). Blue (dark grey), pink (light grey), and grey balls denote nitrogen, boron, and carbon atoms, respectively. The ribbons are periodic and infinitely long along the x direction. The dashed rectangles give the unit cells of the systems. (a) 10 -CNCC-CCBN FIG. 2. The energy bands of armchair BCN nanoribbons: 9 CCCC- NCCB(a), 10 -CCCC-CCBN (b), and 11 -CCCC-CBNC (c). (b) H-H (c) H_down (d) H_up (e) (f) (a) FIG. 3. The energy bands of armchair BCN nanoribbons: 10 -CNCC-CCBN (a), 10 -CNCC-CCBN(H-H)(b), 10 -CNCC-CCBN(H_down) (c) and 10 -CNCC-CCBN(H_up)(d). The spin density of the 10 -CNCC-CCBN(e) and 10 -CNCC-CCBN(H_up)(d) nanoribbon at EF. CNCC-BNCC B or N not pair Band N HM M (total magnetic moment) B: Systems with paired N and B atoms B and N pair or not Band M (total magnetic moment) CCCC-CCCC no HM 0. 3 -0. 6 u. B 1. 0 u. B CCCC-NCCB N HM 1. 0 u. B CCCC-CCCN N HM 1. 0 u. B CCCC-BCCC no HM 0. 7 u. B CNCC-CNCC N HM 1. 0 u. B CNCC-BCCC no HM 0. 7 u. B CCBN-BCCC B MM ~0. 1 u. B CNCC-CCCC no HM 0. 5 u. B CCBN-CCCC B NM 0 CCBC-CCCN no MM 0 FIG. 4. The spin-unpolarized density of states of 7 -CCCC, 11 -CNCC-BCCC, 12 CCBC-CCBN -CNCC-CCCC and 12 -CCCC–BCCC nanoribbons. no NM 0 no MM 0 CCBC-CCBC B MM 0. 5 -0. 1 u. B CCBC-CCCC B NM 0 There is a very sharp peak at Fermi level for nanoribbons in the FIG. 4. According to Stoner Rule, there is a spin splitting at Fermi level CCBN-CCBN Conclusion: CNCC-BNCC, CCCC-NCCB, CCCC-CCCN, and CNCC-CNCC nanoribbon that with N not paired to B presents halfmetal with the total magnetic monment 1. 0 u. B. For CNCC-BNCCand CNCC-CNCC armchair can change to spin gapless semiconductors (SGS) from HM where the up edge saturated with H. Magnetism is found in CCCC-CCCC, CCCC-BCCC, CNCC-CCCC system where B and N atoms pair to each other. It can be explained well according to Stoner Rule.
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