ESR evidence for disordered magnetic phase from ultra-small carbon nanotubes embedded in zeolite nanochannels

A multi-frequency electron spin resonance (ESR) study provides evidence for the occurrence of low-temperature ferromagnetic/spin-glass behavior in aligned arrays of sub-nanometer single-walled carbon nanotubes confined in zeolite nanochannels, owing to sp2-type non-bonding carbon-associated localized states with density of ≈3×1019/g. Features related to the much anticipated conduction ESR are not detected. In the paramagnetic phase, the ESR linewidth is found to be weakly dependent on microwave frequency.