Magnetic phase transition for defect induced electron spins from fully metal–semiconductor separated SWCNTs

摘要

ESR experiments from PtRhRe grown and highly semiconductor—metal separated single-walled carbon nanotubes(SWCNTs) were performed at 9.45 GHz and temperatures Tbetween 0.39 and 200 K. No explicit evidence was found for aresponse from itinerant electrons in the metallic tubes. Rather,in both the metallic (M) and the semiconducting (SC) tubes,the ESR signal originates from quasi-localized defect spinsbut interactions with free electrons render the two systemscharacteristically different. The spin susceptibility was ofCurie–Weiss type for T≥10 K. For annealed samples it dropsfor lower T indicating a transition to a ferromagnetic state.Linewidths decrease and increase with increasing T for M andSC tubes, respectively. As a consequence they cross for the twosystems. Interaction of spins with free carriers in M tubes viaan RKKY type mechanism and increase of linewidth withtemperature for SC tubes due to spin–lattice interaction issuggested to be responsible for this.