Antiferromagnetic behavior in single-wall carbon nanotubes

Abstract

The electronic properties of single-wall carbon nanotubes (SWNTs) have been studied using dc magnetization and electron spin resonance (ESR). The dc magnetization displays a weak diamagnetic susceptibility of $\ensuremath{\approx}{10}^{\ensuremath{-}7}\phantom{\rule{0.3em}{0ex}}\mathrm{emu}∕\mathrm{g}$. ESR measurements reveal a narrow resonance line of low intensity and metallic line shape. The spin susceptibility shows a major Pauli contribution at high temperatures $(T>150\phantom{\rule{0.3em}{0ex}}\mathrm{K})$ and an appreciable Curie component at lower temperatures. A marked drop of the spin susceptibility is observed at $T<14\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, pointing to the opening of a spin gap at low temperatures. The underlying mechanism is discussed in terms of an electronic instability of the SWNTs or the occurrence of defect-mediated spin magnetism.