Magnetic heterogeneity and alignment of single wall carbon nanotubes

Magnetic alignment studies demonstrate that a fraction of acid purified single wall carbon nanotubes (SWNTs) exhibit both linear-orbital (diamagnetic and/or paramagnetic) and ferromagnetic (FM) anisotropies, The latter are unexpected, as prior studies have assumed that remaining FM impurities are encapsulated and play no role in SWNT alignment. The data imply a FM easy axis aligned with the nanotube, permit direct estimates of the FM moment size, and provide a more accurate measure of the SWNT.magnetic anisotropy. In light of recent observations of FM proximity effects in nanotubes, our observation of attached or intrinsic FM anisotropy in these systems is an important consideration for future studies of carbon nanotube magnetism.