Ferromagnetism in Graphene Nanoribbons: Split versus Oxidative Unzipped Ribbons

• Published in: Nano letters Vol. 12; no. 3; pp. 1210 - 1217
• Main Authors: Rao, S. S, Jammalamadaka, S. Narayana, Stesmans, A, Moshchalkov, V. V, Tol, J. van, Kosynkin, D. V, Higginbotham-Duque, A, Tour, J. M
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 14-03-2012
• Subjects: Clusters; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Cross-disciplinary physics: materials science; rheology; Crystallization - methods; Electromagnetic Fields; Electron paramagnetic resonance; Electron spin resonance; Exact sciences and technology; Exchange; Ferromagnetism; Fullerenes and related materials; diamonds, graphite; Graphene; Graphite - chemistry; Macromolecular Substances - chemistry; Magnetic properties; Magnetic properties and materials; Magnetic properties of nanostructures; Magnets; Materials science; Materials Testing; Molecular Conformation; Nanostructure; Nanostructures - chemistry; Nanostructures - ultrastructure; Oxidation-Reduction; Particle Size; Physics; Ribbons; Small particles and nanoscale materials; Specific materials; Studies of specific magnetic materials; Surface Properties; HYSCORE; Magnetism; graphene nanoribbons; ESR; exchange bias; Experimental result; Magnetization; Graphene; Ferromagnetic materials; Nanotape; Electron paramagnetic resonance; Carbon; Potassium; Magnetic properties
• ISSN: 1530-6984; 1530-6992
• DOI: 10.1021/nl203512c

Two types of graphene nanoribbons: (a) potassium-split graphene nanoribbons (GNRs), and (b) oxidative unzipped and chemically converted graphene nanoribbons (CCGNRs) were investigated for their magnetic properties using the combination of static magnetization and electron spin resonance measurements. The two types of ribbons possess remarkably different magnetic properties. While a low-temperature ferromagnet-like feature is observed in both types of ribbons, such room-temperature feature persists only in potassium-split ribbons. The GNRs show negative exchange bias, but the CCGNRs exhibit a “positive exchange bias”. Electron spin resonance measurements suggest that the carbon-related defects may be responsible for the observed magnetic behavior in both types of ribbons. Furthermore, information on the proton hyperfine coupling strength has been obtained from hyperfine sublevel correlation experiments performed on the GNRs. Electron spin resonance finds no evidence for the presence of potassium (cluster) related signals, pointing to the intrinsic magnetic nature of the ribbons. Our combined experimental results may indicate the coexistence of ferromagnetic clusters with antiferromagnetic regions leading to disordered magnetic phase. We discuss the possible origin of the observed contrast in the magnetic behaviors of the two types of ribbons studied.