Stability of the antiferromagnetic ground state in strained finite-sized zigzag carbon nanotubes

DALOSTO, S.D; RUIZ, CARLOS; SILVIA TINTE

San Francisco

Congreso; American Chemical Society; 2014

American Chemical Society

It was recently reported that the ground state of an open-ended finite-sized zigzag and hydrogen atoms terminated carbon nanotube (CNT) is antiferromagnetic (AFM) (Hod, O.; Scuseria, G. E. ACS Nano 2008, 2, 2243). The AFM spin density consists in spin up at one edge and spin down at the opposite one. The energy difference (ΔE = EFM -EAFM) with the above lying higher spin multiplicity ferromagnetic state decreases monotonically with the length of the CNT, and ms can change from 1 to 3 depending on the length and diameter of the CNT. Interestingly, for lengths superiors to 2.8 nm, ΔE is lower than 1 kBT (T = 298 K) which has motivated us to computationally investigate the possibility to turn the AFM ground state of short-segment CNT to a FM state by mean of longitudinal, radial and torsional strain. We study CNT(7,0,L) with a diameter 0.55 nm and length L = 0.93, 1.56, 2.20, 2.85, 3.38 nm. For all the studied strains, we found that the AFM ground state is preserved and the above lying FM state has ms = 2. (i) For longitudinal compressive strains, ΔE increases thus the AFM state is the most favorable state . Instead, as the expansive strain increases, first ΔE decreases destabilizing the AFM state until a strain value of ∼7% is reached. Then for higher strain, ΔE increases. (ii) For compressive radial strain, ΔE decreases up to ∼0.004 KBT at the maximum strain imposed of 14%. This result indicates that this is the correct avenue to obtain a FM state. For expansion of radial strain, the AFM state becomes more stable. (iii) Torsion strain stabilizes the AFM and was not further studied. We rationalized the finding in terms of the spin-spin interaction and propose a possible way to obtain nanomagnetism in pristine but strained finite-sized zigzag CNTs.