Magnetization in CNT induced by nitrogen doping and enhanced by transversal electric field application

Density-functional theory (DFT) is employed to study the induced magnetization in nitrogen-doped arm-chair carbon nanotubes (ACNT:N) and assess the effect of application of electric field. Three fashions of dopants’ distributions were considered: (i) N-dopant atoms in a sequence of a chain along the ACNT; (ii) N-dopant atoms in alternating position with carbon atoms in a chain along the ACNT; and (iii) N-dopant atoms randomly distributed on the surface of ACNT. The results show that: (a) In absence of electric field, pristine and randomly N-doped ACNTs are paramagnetic. (b) Ferromagnetism/anti-ferromagnetism can be achieved when N-dopant atoms are close like in (sequenced or alternating) chain with number of N-dopant atoms odd/even, respectively. (c) Critical transversal electric field Fc ≅ 2 V/Å is needed for bandgap ionization of zigzag CNT (ZCNT) and found to be in excellent agreement with the experimental data. (d) Stronger transversal electric fields, F ≥ 4 V/Å, would be able to induce magnetization in ACNT:N. Assuming z-direction to be along the ACNT axle, then N-atom’s P_z orbital would contribute to σ-bonding whose energies are far deeper away from Fermi energy; so M_z = 0, and M→ = M_xi^ + M_yj^ would always be radical to ACNT:N. The strong transversal field has the ability to tune the contributions of the π-bond electrons into building up the magnetization causing ferromagnetism and anti-ferromagnetism. Our results are benchmarked to the experimental data and theoretical results available in the literature. The relevance of our work to spintronic and gas-sensing devices is further discussed. Graphical abstract: [Figure not available: see fulltext.]