Journal
NANO LETTERS
Volume 12, Issue 3, Pages 1210-1217Publisher
AMER CHEMICAL SOC
DOI: 10.1021/nl203512c
Keywords
Magnetism; graphene nanoribbons; exchange bias; ESR; HYSCORE
Categories
Funding
- Flemisch Government
- IAP network of the Belgian Government
- NSF [DMR-0654118]
- State of Florida
- Federal Aviation Administration [2007-G-010]
- Air Force Office of Scientific Research [FA9550-09-1-0581]
- Air Force Research Laboratory through University Technology Corporation [09-S568-064-01-C1]
- MI-SWACO
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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 dusters 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.
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