Journal
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS
Volume 401, Issue -, Pages 70-76Publisher
ELSEVIER
DOI: 10.1016/j.jmmm.2015.10.012
Keywords
Graphene; Doping; Ferromagnetic ordering; Defects; Density functional theory; X-ray photoelectron spectroscopy; Magnetization
Funding
- DOE-BES-DMS [DEFG02-99ER45795]
- U.S. DOE [DE-AC02- 05CH11231]
- Ohio Supercomputing Center
- NSF [DMR 1307740]
- US National Science Foundation [CMMI-1246800]
- Directorate For Engineering
- Div Of Civil, Mechanical, & Manufact Inn [1246800] Funding Source: National Science Foundation
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While studying magnetism of d- and f-electron systems has been consistently an active research area in physics, chemistry, and biology, there is an increasing interest in the novel magnetism of p-electron systems, especially in graphene and graphene-derived nanostructures. Bulk graphite is diamagnetic in nature, however, graphene is known to exhibit either a paramagnetic response or weak ferromagnetic ordering. Although many groups have attributed this magnetism in graphene to defects or unintentional magnetic impurities, there is a lack of compelling evidence to pinpoint its origin. To resolve this issue, we systematically studied the influence of entropically necessary intrinsic defects (e.g., vacancies, edges) and extrinsic dopants (e.g., S-dopants) on the magnetic properties of graphene. We found that the saturation magnetization of graphene decreased upon sulfur doping suggesting that S-dopants demagnetize vacancies and edges. Our density functional theory calculations provide evidence for: (i) intrinsic defect demagnetization by the formation of covalent bonds between S-dopant and edges/vacancies concurring with the experimental results, and (ii) a net magnetization from only zig-zag edges, suggesting that the possible contradictory results on graphene magnetism in the literature could stem from different defect-types. Interestingly, we observed peculiar local maxima in the temperature dependent magnetizations that suggest the coexistence of different magnetic phases within the same graphene samples. (C) 2015 Elsevier B.V. All rights reserved.
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