Observation of magnetic edge state in graphene nanoribbons

Joly, Vincent; Kiguchi, Manabu; Hao, Si Jia; Takai, Kazuyuki; Enoki, Toshiaki; Sumii, Ryohei; Amemiya, Kenta; Muramatsu, Hiroyuki; Hayashi, T.; Kim, Yoong Ahm; Endo, Morinobu; Campos-Delgado, Jessica; López–Urías, Florentino; Botello-Méndez, Andrés R.; Terrones, Humberto; Terrones, Mauricio; Dresselhaus, M. S.

doi:10.1103/physrevb.81.245428

Cited by 139 publications

(86 citation statements)

References 34 publications

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“…This is nevertheless in agreement with the expected high-temperature stability of s-p electron magnetism 25,26 , as well as experiments reporting room temperature magnetism in defective graphitic samples 5,27,28,29 .…”

supporting

confidence: 78%

Room-temperature magnetic order on zigzag edges of narrow graphene nanoribbons

Magda

Jin

Hagymási

et al. 2014

Nature

707

627

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Magnetic order emerging in otherwise non-magnetic materials as carbon is a paradigmatic example of a novel type of s-p electron magnetism predicted to be of exceptional hightemperature stability 1 . It has been demonstrated that atomic scale structural defects of graphene can host unpaired spins 2,3 . However, it is still unclear under which conditions longrange magnetic order can emerge from such defect-bound magnetic moments. Here we propose that in contrast to random defect distributions, atomic scale engineering of graphene edges with specific crystallographic orientation -comprising edge atoms only from one sublattice of the bipartite graphene lattice -can give rise to a robust magnetic order. We employ a nanofabrication technique 4 based on Scanning Tunneling Microscopy to define graphene nanoribbons with nanometer precision and well-defined crystallographic edge orientations.While armchair ribbons display quantum confinement gap, zigzag ribbons narrower than 7 nm reveal a bandgap of about 0.2 -0.3 eV, which can be identified as a signature of 2 interaction induced spin ordering along their edges. Moreover, a semiconductor to metal transition is revealed upon increasing the ribbon width, indicating the switching of the magnetic coupling between opposite ribbon edges from antiferromagnetic to ferromagnetic configuration. We found that the magnetic order on graphene edges of controlled zigzag orientation can be stable even at room temperature, raising hope for graphene-based spintronic devices operating under ambient conditions.The intrinsic magnetism of graphite has a long and controversial history 1 . The origin of the measured magnetic signal is generally attributed to atomic scale structural defects locally breaking the sub-lattice balance of the bipartite hexagonal lattice 5,6 . However, the unambiguous identification of the structural sources of the measured magnetic signal has proven challenging as they are buried inside the bulk of the material. The isolation of single graphene layers 7 opens new prospects in this direction 8,9 as their atomic structure is fully accessible for imaging and controlled modification. In particular, graphene edges of specific (zigzag) crystallographic orientation comprising carbon atoms from only one sub-lattice of the bipartite hexagonal lattice are predicted to host magnetic order 10 , in striking contrast to armchair edges incorporating an equal number of carbon atoms from both sublattices.The strong influence of edge orientation on the electronic structure of graphene nanoribbons had However, the random orientation of the edges and the influence of a possible strong edge-substrate hybridization 21 did not allow full access to the nature of edge-magnetism in graphene. Though the 4 magnetic order is expected to persist to some extent on zigzag segments of randomly oriented graphene edges, the mixing of different edge types are expected to substantially weaken the effect 19,22 . Therefore, the lack of experimental control over the edge orientation seems one of the main ...

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supporting

confidence: 78%

Room-temperature magnetic order on zigzag edges of narrow graphene nanoribbons

Magda

Jin

Hagymási

et al. 2014

Nature

707

627

View full text Add to dashboard Cite

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“…Permalloy (Py, Ni 80 Fe 20 ) is then deposited by electron-beam evaporation directly followed by a thin Au capping layer, to form contacts 3 and 0.5 mm wide, separated by 1 or 4 mm. After lift-off, a final XeF 2 gas exposure fluorinates the remaining portions of the top graphene layer not covered by the Py contacts to a resistance of 50 GO just before electrical measurement, ensuring that no parallel conductance paths exist, and eliminating possible edge state conduction and possible magnetic effects 37,38 . Further sample fabrication details can be found in the Supplementary Methods and Supplementary Fig.…”

Section: Methodsmentioning

confidence: 99%

Homoepitaxial tunnel barriers with functionalized graphene-on-graphene for charge and spin transport

Friedman

Erve

et al. 2014

Nat Commun

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The coupled imperatives for reduced heat dissipation and power consumption in high-density electronics have rekindled interest in devices based on tunnelling. Such devices require mating dissimilar materials, raising issues of heteroepitaxy, layer uniformity, interface stability and electronic states that severely complicate fabrication and compromise performance. Twodimensional materials such as graphene obviate these issues and offer a new paradigm for tunnel barriers. Here we demonstrate a homoepitaxial tunnel barrier structure in which graphene serves as both the tunnel barrier and the high-mobility transport channel. We fluorinate the top layer of a graphene bilayer to decouple it from the bottom layer, so that it serves as a single-monolayer tunnel barrier for both charge and spin injection into the lower graphene channel. We demonstrate high spin injection efficiency with a tunnelling spin polarization 460%, lateral transport of spin currents in non-local spin-valve structures and determine spin lifetimes with the Hanle effect.

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“…It is interesting to study whether some of these predictions can be extended to finite size multilayer graphene stacks (such as ribbons and flakes). Moreover, due to recent advances in fabrication of less than 10 nm wide nanoribbons with the control of their edge morphology [10][11][12] and observing magnetic edge states in few-layer graphene ribbons 13,14 , our studies of interplay of magnetism and electric field effects in multilayer nanoribbons have important implications in interpreting experiments.…”

Section: Introductionmentioning

confidence: 99%

Effects of edge magnetism and external electric field on energy gaps in multilayer graphene nanoribbons

2010

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Using first principles density functional theory, we study the electronic structure of multilayer graphene nanoribbons as a function of the ribbon width and the external electric field, applied perpendicular to the ribbon layers. We consider two types of edges (armchair and zigzag), each with two edge alignments (referred to as α-and β-alignments). We show that, as in monolayer and bilayer armchair nanoribbons, multilayer armchair nanoribbons exhibit three classes of energy gaps which decrease with increasing width. Non-magnetic multilayer zigzag nanoribbons have band structures that are sensitive to the edge alignments and the number of layers, indicating different magnetic properties and resulting energy gaps. We find that energy gaps can be induced in ABCstacked ribbons with an perpendicular external electric field, while in other stacking sequences, the gaps decrease or remain closed as the external electric field increases.

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Observation of magnetic edge state in graphene nanoribbons

Cited by 139 publications

References 34 publications

Room-temperature magnetic order on zigzag edges of narrow graphene nanoribbons

Room-temperature magnetic order on zigzag edges of narrow graphene nanoribbons

Homoepitaxial tunnel barriers with functionalized graphene-on-graphene for charge and spin transport

Effects of edge magnetism and external electric field on energy gaps in multilayer graphene nanoribbons

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