Long Spin Relaxation Times in Wafer Scale Epitaxial Graphene on SiC(0001)

Maassen, T.; Berg, J. J. van den; IJbema, Natasja; Fromm, Felix; Seyller, Thomas; Yakimova, Rositza; Wees, B. J. van

doi:10.1021/nl2042497

Cited by 122 publications

(101 citation statements)

References 27 publications

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“…After growth, the graphene samples are hydrogenated by an atomic hydrogen source in an ultrahigh vacuum chamber, for different exposure times. Successful hydrogenation is testified by an enhancement of the sp 3 -defect associated Raman D-peak, whose intensity increases with treatment time (Fig. 1c and d), as discussed in more detail in the supplementary information.…”

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confidence: 88%

Interface-Induced Room-Temperature Ferromagnetism in Hydrogenated Epitaxial Graphene

et al. 2013

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Due to the predominantly surface character of graphene, it is highly suitable for functionalization with external atoms and/or molecules leading to a plethora of new and interesting phenomena. Here we show ferromagnetic properties of hydrogenfunctionalized epitaxial graphene on SiC. Ferromagnetism in such a material is not directly evident as it is inherently composed of only non-magnetic constituents. Our results nevertheless show strong ferromagnetism, which cannot be explained by simple magnetic impurities. The ferromagnetism is unique to hydrogenated epitaxial graphene on SiC, where interactions with the interfacial buffer layer play a crucial role. We argue that the origin of the observed ferromagnetism is governed by electron correlation effects of the narrow Si-dangling-bond (Si-DB) states in the buffer layer exchangecoupled to localized states in the hydrogenated graphene layer. This forms a quasithree-dimensional ferromagnet with a Curie temperature higher than 300 K.Owing to its capability of ballistic transport over micrometer distances 1 , as well as its very long spin relaxation time and spin relaxation length 2, 3 , graphene represents a close-to-ideal material for spintronic applications 4 . In this context, considerable effort has recently been directed to rendering graphene ferromagnetic via chemical modification. Thus far, ferromagnetic order in graphene has been attained through covalent functionalization, involving the linkage of radical species like the spin-bearing carbon atom of an organic molecule or hydrogen atoms to the graphene layer [5][6][7][8][9][10][11][12][13][14][15][16][17] . Along these lines, functionalization of epitaxial graphene by aryl radicals has been reported to yield disordered magnetism, comprising a mixture of ferromagnetic, superparamagnetic and antiferromagnetic regions 18 .With the aid of combined atomic and magnetic force microscopy, it could be proven that these randomly dispersed regions are constituted by the attached moieties. This lack of a periodic functionalization pattern of the graphene sheet prevents the achievement of long range ferromagnetic order, thus limiting the use of such samples in spintronic devices.Furthermore, room temperature ferromagnetism has been detected in partially hydrogenated epitaxial graphene grown on silicon carbide (SiC), and attributed to hydrogen monomers bonded to the graphene sheet 12 . Despite these accomplishments, however, both the mechanism underlying the ferromagnetic ordering, and the role played by the SiC substrate used for the epitaxial graphene growth, has not yet been clarified. Here, we experimentally demonstrate that spin ordering within hydrogenated epitaxial graphene critically depends on the presence of the underlying buffer layer. In addition, it is shown that the created magnetic 3 areas are distributed over the entire graphene sheet, thus enabling to effectively tune the overall magnetization through the density of attached hydrogen atoms.To explore the ferromagnetism in epitaxial graphene, we use samples ...

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confidence: 88%

Interface-Induced Room-Temperature Ferromagnetism in Hydrogenated Epitaxial Graphene

et al. 2013

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“…5,6 The initial spin transport studies were mainly performed on single-layer [7][8][9][10] and bilayer exfoliated graphene, 9,11 and large-area graphene [12][13][14][15] deposited on conventional SiO 2 substrates. Although enhanced spin-relaxation times have been reported for bilayer graphene-based devices compared with those based on a single layer, the relatively low spin diffusion constants overall yield a lower spin-relaxation length of only 1-2 μm, 9,11 far below the theoretical predictions.…”

Section: Introductionmentioning

confidence: 99%

Electronic spin transport in dual-gated bilayer graphene

et al. 2016

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The elimination of extrinsic sources of spin relaxation is key to realizing the exceptional intrinsic spin transport performance of graphene. Toward this, we study charge and spin transport in bilayer graphene-based spin valve devices fabricated in a new device architecture that allows us to make a comparative study by separately investigating the roles of the substrate and polymer residues on spin relaxation. First, the comparison between spin valves fabricated on SiO 2 and BN substrates suggests that substrate-related charged impurities, phonons and roughness do not limit the spin transport in current devices. Next, the observation of a fivefold enhancement in the spin-relaxation time of the encapsulated device highlights the significance of polymer residues on spin relaxation. We observe a spin-relaxation length of~10 μm in the encapsulated bilayer, with a charge mobility of 24 000 cm 2 Vs − 1 . The carrier density dependence on the spin-relaxation time has two distinct regimes; no4 × 10 12 cm − 2 , where the spin-relaxation time decreases monotonically as the carrier concentration increases, and n ⩾ 4 × 10 12 cm − 2 , where the spin-relaxation time exhibits a sudden increase. The sudden increase in the spin-relaxation time with no corresponding signature in the charge transport suggests the presence of a magnetic resonance close to the charge neutrality point. We also demonstrate, for the first time, spin transport across bipolar p-n junctions in our dual-gated device architecture that fully integrates a sequence of encapsulated regions in its design. At low temperatures, strong suppression of the spin signal was observed while a transport gap was induced, which is interpreted as a novel manifestation of the impedance mismatch within the spin channel. INTRODUCTIONGraphene is considered to be a promising spin-channel material for future spintronics applications 1 because of its high-electronic mobility, 2 weak spin-orbit coupling 3,4 and a negligible hyperfine interaction. 5,6 The initial spin transport studies were mainly performed on single-layer 7-10 and bilayer exfoliated graphene, 9,11 and large-area graphene 12-15 deposited on conventional SiO 2 substrates. Although enhanced spin-relaxation times have been reported for bilayer graphene-based devices compared with those based on a single layer, the relatively low spin diffusion constants overall yield a lower spin-relaxation length of only 1-2 μm, 9,11 far below the theoretical predictions. 16 One approach suggested for achieving a longer distance spin communication is to increase the spin diffusion constants by fabricating higher mobility devices. 8,17 For charge transport, it has been shown that the carrier mobility of graphene devices on SiO 2 is mainly limited by interfacial charged impurities, surface roughness, and phonons. [18][19][20] The demonstration of an order-of-magnitude improvement in the mobility of graphene encapsulated between atomically flat, charge trap free boron nitride crystals 21,22 has triggered the recent spin transport studies...

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“…However, the spin injection measurements based on a non-local spin valve geometry [44,54,55] revealed surprisingly short spin relaxation times of only about 100 − 200ps, being only weakly dependent on the charge density and temperature. The longest spin relaxation time has been measured up to now is also in the order of a few ns [88]. There are many explanations for short spin relaxation times in graphene.…”

Section: Spin Transport In Disordered Graphenementioning

confidence: 98%

Charge and Spin Transport in Disordered Graphene-Based Materials

Tuan

2016

Springer Theses

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Long Spin Relaxation Times in Wafer Scale Epitaxial Graphene on SiC(0001)

Cited by 122 publications

References 27 publications

Interface-Induced Room-Temperature Ferromagnetism in Hydrogenated Epitaxial Graphene

Interface-Induced Room-Temperature Ferromagnetism in Hydrogenated Epitaxial Graphene

Electronic spin transport in dual-gated bilayer graphene

Charge and Spin Transport in Disordered Graphene-Based Materials

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