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

• Published in: physica status solidi (b) Vol. 249; no. 12; pp. 2562 - 2567
• Main Authors: Havlicek, M., Chernov, A., Jantsch, W., Wilamowski, Z., Yanagi, K., Kataura, H., Rümmeli, M. H., Malissa, H., Kuzmany, H.
• Format: Journal Article
• Language: English
• Published: Berlin WILEY-VCH Verlag 01-12-2012; WILEY‐VCH Verlag
• Subjects: ESR; magnetic phase transition; SC-M separation; SWCNT
• ISSN: 0370-1972; 1521-3951
• DOI: 10.1002/pssb.201200426

ESR experiments from PtRhRe grown and highly semiconductor—metal separated single‐walled carbon nanotubes (SWCNTs) were performed at 9.45 GHz and temperatures T between 0.39 and 200 K. No explicit evidence was found for a response 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 spins but interactions with free electrons render the two systems characteristically different. The spin susceptibility was of Curie–Weiss type for T ≥ 10 K. For annealed samples it drops for lower T indicating a transition to a ferromagnetic state. Linewidths decrease and increase with increasing T for M and SC tubes, respectively. As a consequence they cross for the two systems. Interaction of spins with free carriers in M tubes via an RKKY type mechanism and increase of linewidth with temperature for SC tubes due to spin–lattice interaction is suggested to be responsible for this.