Magnetic anisotropies of aligned carbon nanotubes

Angle-dependent conduction-electron spin resonance and static magnetic-susceptibility measurements of bulk, aligned, and partially purified carbon nanotube films show anisotropies reflecting the anisotropic character of the tubes. The Pauli susceptibility (above 40 K) of the tubes corresponds to about 10¹⁸ spins/cm³, consistent with a semimetal. The g factors and their anisotropies are temperature dependent. The intrinsic tube resistivity is approximately an order of magnitude lower than the dc resistivity of the films. Qualitative changes below 40 K in the resistivity, the spin susceptibility, the g factors, and their anisotropies give evidence for charge-carrier localization.