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Bistability in Fe, Co and Ni Wires Inside Carbon Nanotubes

Rodrigues RB and Diniz EM

Encapsulation of nanowires by carbon nanotubes is a very efficient manner of protect the nanowire from external influences, as oxidation. Moreover, it permits to produce strictly linear chains of atoms if the carbon nanotube is very narrow. Although many theoretical studies have been performed concerning this subject, a few take in account the effects of the Peierls distortion, which dimerizes the chain. To contribute to this topic, here we report first principles calculations based on density functional theory of Fe, Co and Ni nanowires encapsulated by narrow zigzag or armchair carbon nanotubes. Ours findings predict that Fe nanowire has a minimum energy configuration for a dimerized geometry and a deep local minimum for a non-dimerized one. Also we find that Co and Ni have a regular-spaced configuration as the lowest-energy geometry, but Co nanowire exhibits a local minimum for a dimerized configuration, whose energy barrier is independent on the nanotube diameter and chirality. Moreover we find that all nanowires transfer electrons to the nanotube and the magnetic moments of the dimerized nanowires are at least 50% smaller than the corresponding for the non-dimerized ones. In some cases there exists a vanishing of the magnetic moment even when the non-dimerized nanowire has a non-zero value. Such findings can help to predict structural, electronic and magnetic properties of nanowires encapsulated by carbon nanotubes and give an insight concerning if the differences of those two geometries for the nanowires can produce experimentally detectable data.