  We report the observation of the intrinsic magnetic susceptibility of highly
purified SWCNT samples prepared by a combination of acid treatment and density
gradient ultracentrifugation (DGU). We observed that the diamagnetic
susceptibility of SWCNTs increases linearly with increasing nanotube diameter.
We found that the magnetic susceptibility divided by the diameter is a
universal function of the scaled temperature. Furthermore, the estimated
magnetic susceptibilities of pure semiconducting and pure metallic SWCNT
samples suggest that they respond differently to changes in carrier density,
which is consistent with theory. These findings provide experimental
verification of the theoretically predicted diameter, temperature, and
metallicity dependence of the magnetic susceptibility.
