Intrinsic Magnetism in Single-Walled Carbon Nanotubes of Finite Length

Abstract

The magnetic properties of axially confined hydrogenated single-walled carbon nanotubes (SWCNTs) of the (n, 0) type, as well as cross-linking architectures based on these units, are systematically explored by use of density functional theory. Emphasis is placed on the relation between the ground state magnetic moments of SWCNTs and zigzag graphene nanoribbons (ZGNRs). Comparison between SWCNTs with n = 5–24 and ZGNRs of equal length gives rise to two basic questions: (1) how does the nanotube curvature affect the antiferromagnetic order known to prevail in ZGNRs, and (2) to what extent do the magnetic moments localized at the SWCNT edges deviate from the zero-curvature limit n/3 μ_B? The studies on single SWCNTs are extended to cross-linking carbon nanotubes (CLCNTs) composed of three axially confined single-walled carbon nanotubes (SWCNTs) of the (10,0) type. Three CLCNT models, differing from each other by the structure of the contact regions of the three SWCNT constituents, are explored in terms of their geometric, electronic, and magnetic properties. Various magnetic phases, as obtained by combining finite SWCNTs in ferromagnetic (FM) or antiferromagnetic (AFM) coordination, are distinguished. The characteristics of these phases are shown to depend on the contact region geometry which plays an essential role in defining the order of their stabilities. Prospects of applying either of the two systems analyzed here, SWCNTs and CLCNTs, as transmission elements in spintronics are discussed.