Electron spin resonance of K-doped single-wall carbon nanohorns and single-wall carbon nanotubes

K-doping into the aggregate of single-wall carbon nanohorns (SWNHs) and into the bundle of single-wall carbon nanotubes (SWNTs) are introduced in this study. Electron spin resonance (ESR) of the pristine SWNHs and SWNTs show that the pristine SWNHs are ESR active and the linewidth (Delta H) is susceptive to the partial pressure of O-2, while the pristine SWNTs are ESR silent. Delta H of K-doped SWNHs becomes wider by a factor of similar to 2 than that of the pristine one. For K-doped SWNTs, the Dysonian type ESR comes to be observed. Details of the ESR features are discussed.