Paramagnetic transitions and weak-diamagnetism in sulfur-doped buckypapers and graphene-oxide composites

The appearance of coexisting ferromagnetic and superconductive phenomena in graphite‑sulfur and amorphous carbon‑sulfur composites has recently attracted an important attention. In this work we propose a novel re-investigation of the carbon‑sulfur doping mechanism performed by employing carbon nanotube networks (cm-scale buckypapers) and graphene-oxide films as host-materials. In the buckypaper-case, the presence of multiple sulfidation processes involving formation of 1) carbon‑sulfur and 2) metal-sulfide phases was demonstrated. Presence of carbon‑sulfur bonding was identified by employing both Raman spectroscopy and X-ray photoelectron spectroscopy. The conductive and magnetic properties of the sulfur-rich areas within the buckypaper were also investigated. An enhanced carbon‑sulfur bonding was then identified in sulfur-doped graphene-oxide films. In this latter case we demonstrate an almost complete annihilation of ferromagnetic-signals. ESR-spectroscopy of this second-type of system revealed the appearance of a paramagnetic transition for g ~ 2.08 at T ~ 77 K, possibly originating from the carbon‑sulfur bonding. A weak enhancement in the diamagnetic component could be interestingly detected below T ~ 60 K as a consequence of sulfur doping, after subtraction of the percolative ferromagnetic signals.