Magnetism of adsorbed oxygen on carbon nanohorns

Magnetic susceptibilities for adsorbed O2 on heat-treated single-wall carbon nanohorns (HT-SWNHs) showed anomalous features as compared with those on as-grown SWNHs. Magnetism for the latter case was similar to that for bulky solid O2, indicating the magnetic phase transitions associated with gaseous to liquid and in solid states (γ–β and β–α). On the other hand, magnetism associated with γ–β transition was not observed for O2 adsorbed on HT-SWNHs. For HT-SWNHs, O2 can get into the interior of SWNH from the nano-windows, which were opened by heat-treatment, and solidify. We therefore concluded that the γ–β transition was suppressed in the nano-meter sized space.