Half-metallic finite zigzag single-walled carbon nanotubes from first principles

Abstract

Density-functional calculations predict half-metallicity in zigzag single-walled carbon nanotubes of finite length with the two ends saturated with hydrogen. We have analyzed the change of the ␣-and ␤-spin electronic gaps under the influence of an electric field applied along the nanotube axis. The half-metallic behavior, in which the electronic gap is zero for one spin flavor and nonzero for the other, is obtained for a critical electric field of 3.0/ w V / Å, where w is the length of the nanotube. This critical field is the same as that predicted for graphene nanoribbons. By a detailed analysis of the spin structure of the ground state, we show the relevance of the edge states, electronic states spatially localized at the carbon atoms of the nanotube boundaries, on the on-set of half-metallicity, and on the magnetic properties of the finite semiconducting zigzag nanotubes.

van der Waals interaction in magnetic bilayer graphene nanoribbons

“…We find that the magnetic moments are mainly located at the edges and decay exponentially when moving into the central part of the ribbon, in agreement with previous results. 10,39 Notice that the interlayer interaction between edges suppresses the site magnetization: for the planar cases, the magnetization value is about 0.25μ b . This is the case for all the magnetic configurations with AB β stacking and the AB α ones with FM intralayer coupling; see Fig.…”

“…5(a). 10,39 It should be noted that the nanoribbon gaps may be underestimated in a GGA calculation. 40 The use of other functionals, such as the hybrid Heyd-Scuseria-Ernzerhof, 41 would correct this effect; in any case, the gap decrease with increasing width and the abrupt jumps associated with the magnetic changes will certainly hold in calculations employing other functionals, but with the quenching of magnetic moments taking place at larger widths.…”

Electronic and magnetic properties of Fe clusters inside finite zigzag single-wall carbon nanotubes

“…16 Our aim is to analyze the interplay between the singular magnetic properties of the finite ZNTs and the large magnetization of the encapsulated Fe clusters. As we have shown in a previous work, 15 the ZNTs present electronic properties associated to edge states similar to those of zigzag graphene ribbons, 17 therefore our study could be of relevance in analyzing the properties of proposed magnetoresistive devices based on zigzag graphene ribbons. 18 Furthermore, as far as finite ZNTs can be considered as organic molecules containing π electrons, our results can be useful in the interpretation of the local spin polarization at the organicferromagnetic interface, which has been recently described both theoretically and experimentally.…”

“…As for other finite ZNTs, 15 the ground state presents an AFM spin configuration along the tube, with zero total magnetic moment (μ T = 0). As an example, the spin structure of the ground state of the long (10,0) ZNT is given in Fig.…”

“…The two ends show opposite orientation of the atomic magnetic moments. [12][13][14][15] Other states are close in energy to the ground state: magnetic states (M) with net total magnetic moment μ T different from zero (in some of these, the magnetic moments at the two edges show the same orientation [13][14][15], and a nonmagnetic (NM) state showing local spin compensation along the nanotube. The energy difference E(μ 0 T ) − E(AFM) between the lowest-lying magnetic state (with total magnetic moment μ 0 T ) and the ground state (AFM) decreases monotonically when the length of the nanotube increases, up to a point where the difference becomes lower than room temperature.…”