Non-equilibrium processing of ferromagnetic heavily reduced graphene oxide

Discovery of ferromagnetism with simultaneous bandgap opening in graphene[1] provides an attractive platform towards multifunctional spintronic devices. However, device integration of graphene and reduced graphene oxide (rGO) is hindered by scalability and high temperature required for reducing GO....

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Bibliographic Details
Published in:Carbon (New York) 2019-11, Vol.153, p.663-673
Main Authors: Gupta, Siddharth, Narayan, Jagdish
Format: Article
Language:English
Subjects:
Band gap
Carbon
Carrier density
Coercivity
Crossovers
Direct laser writing
Electron mobility
Energy gap
Ferromagnetism
Graphene
High temperature
Magnetic properties
Magnetic saturation
Magnetism
Magnetoresistance
Magnetoresistivity
Position (location)
Raman spectroscopy
Spin-orbit interactions
Supercooling
Temperature dependence
Thin films
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Summary:Discovery of ferromagnetism with simultaneous bandgap opening in graphene[1] provides an attractive platform towards multifunctional spintronic devices. However, device integration of graphene and reduced graphene oxide (rGO) is hindered by scalability and high temperature required for reducing GO. In this paper, we present a nonequilibrium approach for direct laser writing heavily reduced GO films by melting amorphous carbon in ambient conditions. Nanosecond laser irradiation melts carbon, which regrows into rGO in low undercooling conditions. These rGO films exhibit room-temperature ferromagnetism with a high saturation magnetization of 7.0 emu/g and 40 Oe coercivity. The intrinsic ferromagnetic ordering triggers a broad negative magnetoresistance (MR) cusp from 20 to 50 K. An anomalous crossover from weak localization (WL) to weak antilocalization (WAL) is observed below 5 K, suggesting a substantial enhancement in spin-orbit coupling strength, opening a new route to access topological states in rGO. The rGO films exhibit 12.6 cm2/Vs electron mobility with n-type carrier concentration of 1.2 × 1021/cc. Raman spectroscopy and temperature-dependent transport investigations in rGO suggest low-disorder, following 2D Mott variable range hopping (VRH) mechanism with a bandgap of ∼0.22 eV and 3 nm localization length. These findings open a definitive pathway for tuning electrical and magnetic properties in graphene-based materials with laser-writing. [Display omitted]
ISSN:0008-6223
1873-3891
DOI:10.1016/j.carbon.2019.07.064