Unique magnetism observed in single-wall carbon nanohorns

The magnetic properties of single-wall carbon nanohorns (SWNH) were studied by electron spin resonance (ESR) and static magnetic susceptibility measurements. The SWNHs were ESR active with linewidth (DeltaH) of similar to 6 G in vacuo at room temperature. DeltaH was susceptible to the partial pressure Of O-2 and became 53 G at I atmospheric pressure of O-2, while the integrated ESR intensity was independent on O-2 pressure and behaved as Curie-like, suggesting an intrinsic ESR origin with localized electron spin character. The diamagnetic susceptibility for SWNHs indicated a value smaller than that of randomly oriented graphite by an order of magnitude, but showing a magnitude comparable to those Of C-60 and C-70. It is suggested that the large diamagnetism expecting for sp(2) networked carbon materials will be canceled by the Van Vleck constant paramagnetism.