Electrical Spin Injection into Graphene through Monolayer Hexagonal Boron Nitride

Yamaguchi, Takeshi; Inoue, Yoshihisa; Masubuchi, Satoru; Morikawa, Sei; Onuki, Masahiro; Watanabe, Kenji; Taniguchi, Takashi; Moriya, Rai; Machida, Tomoki

doi:10.7567/apex.6.073001

Cited by 99 publications

(99 citation statements)

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“…Metal, semiconductor, and insulator 2D materials have been studied, and various functional electronics and opto-electronics devices have been demonstrated with these materials [4][5][6][7]. Further, these 2D materials could be potentially applied in the field of spintronics [8]; for example, long-distance spin transport has been demonstrated in graphene/h-BN heterostructures [9], and spin polarized tunneling has been demonstrated through graphene [10] and h-BN [11,12]. In these experiments, the source for the spin-polarized electrons is a ferromagnetic metal fabricated by the evaporation technique; thus, the interface between the ferromagnetic and non-magnetic materials involves chemical bonding.…”

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confidence: 99%

Construction of van der Waals magnetic tunnel junction using ferromagnetic layered dichalcogenide

Arai

Moriya

Yabuki

et al. 2015

Applied Physics Letters

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We investigate the micromechanical exfoliation and van der Waals (vdW) assembly of ferromagnetic layered dichalcogenide Fe 0.25 TaS 2 . The vdW interlayer coupling at the Fe-intercalated plane of Fe 0.25 TaS 2 allows exfoliation of flakes. A vdW junction between the cleaved crystal surfaces is constructed by dry transfer method. We observe tunnel magnetoresistance in the resulting junction under an external magnetic field applied perpendicular to the plane, demonstrating spin-polarized tunneling between the ferromagnetic layered material through the vdW junction.*E-mail: moriyar@iis.u-tokyo.ac.jp; tmachida@iis.u-tokyo.ac.jp 2 Recently, studies on two-dimensional (2D) materials such as graphene, hexagonal boron nitride (h-BN), and transition metal dichalcogenides (TMDs) have received considerable attention [1,2]. These materials exhibit layered structure in the bulk form, and the van der Waals (vdW) force connects each of the layers. Thus, these crystals can easily be exfoliated down to monolayer and used to construct heterostructures of different 2D materials connected by vdW force [3]. Metal, semiconductor, and insulator 2D materials have been studied, and various functional electronics and opto-electronics devices have been demonstrated with these materials [4][5][6][7]. Further, these 2D materials could be potentially applied in the field of spintronics [8]; for example, long-distance spin transport has been demonstrated in graphene/h-BN heterostructures [9], and spin polarized tunneling has been demonstrated through graphene [10] and h-BN [11,12]. In these experiments, the source for the spin-polarized electrons is a ferromagnetic metal fabricated by the evaporation technique; thus, the interface between the ferromagnetic and non-magnetic materials involves chemical bonding. On the other hand, the vdW interface does not require any chemical bonding at the junction, in principle. Therefore, layered ferromagnetic 2D materials could possibly be used for constructing vdW heterostructures with spintronic functions. Moreover, the vdW hetrostructure could provide another degree of freedom that has not been possible in the conventional spintronics device; such as controlling the interlayer twist [13,14] In Fig. 1(c), optical micrographs of the exfoliated flake and their vdW junction are shown. The area of vdW junction is 67.8 µm 2 . The quality of the vdW interface is analyzed using cross-sectional transmission electron microscopy (TEM), as shown in Fig. 1(d). The TEM image revealed the layered structure of each Fe 0.25 TaS 2 flake with a stacking period of 0.61 nm; this period is close to the reported value for the bulk material [18]. The vdW contact between the flakes is clearly visible in the TEM image [ Fig. 1(d)].The TEM reveals that vdW junction displays different TEM contrast from the flake; this behavior is attributed to the presence of a native oxide layer existing at the surface of cleaved Fe 0.25 TaS 2 . The presence of Ta 2 O 5 oxide layer in the topmost layer of the exfoliated Fe 0.25 TaS 2 surface i...

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confidence: 99%

Construction of van der Waals magnetic tunnel junction using ferromagnetic layered dichalcogenide

Arai

Moriya

Yabuki

et al. 2015

Applied Physics Letters

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“…Tunnel devices typically require mating dissimilar materials and maintaining monolayer level control of thickness, raising issues that severely complicate fabrication and compromise performance. The recent discoveries of intrinsically twodimensional (2D) materials 4 , such as graphene and h-BN have created new perspectives on tunnel barriers [5][6][7][8] . Their strong inplane bonding promotes self-healing of pinholes 9 and a welldefined layer thickness, important because the tunnel current depends exponentially on the barrier thickness.…”

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“…In addition, the mobility of graphene is significantly degraded by coupling to phonons or charged impurities/defects in an adjacent oxide. Consequently, significant effort has focused on exploiting other carbon-thin films and 2D materials such as h-BN or MoS 2 as a substrate, gate dielectric or tunnel barrier for graphene devices 7,8,10,18,19 . This improves operating characteristics, but significantly complicates the fabrication, and often relies on sequential mechanical exfoliation to produce a few device structures.…”

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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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“…5,6 The latest findings of intrinsically 2-D materials, 7 like h-BN and graphene have formed new perceptions on tunnel barriers. [8][9][10][11] It is interesting to utilize graphene a 2-D material comprising a single sheet of carbon atoms organized in a honeycomb lattice arrangement, as a highmobility transport tunnel barrier. Graphene shows unique in-plane spin transport properties as well, including long spin diffusion lengths due to its low spin-orbit coupling, [12][13][14] which has fueled ideas for novel spin based devices.…”

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Tuning the tunneling magnetoresistance by using fluorinated graphene in graphene based magnetic junctions

Meena

Choudhary

2017

AIP Advances

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Spin polarized properties of fluorinated graphene as tunnel barrier with CrO2 as two HMF electrodes are studied using first principle methods based on density functional theory. Fluorinated graphene with different fluorine coverages is explored as tunnel barriers in magnetic tunnel junctions. Density functional computation for different fluorine coverages imply that with increase in fluorine coverages, there is increase in band gap (Eg) of graphene, Eg ∼ 3.466 e V was observed when graphene sheet is fluorine adsorbed on both-side with 100% coverage (CF). The results of CF graphene are compared with C4F (fluorination on one-side of graphene sheet with 25% coverage) and out-of-plane graphene based magnetic tunnel junctions. On comparison of the results it is observed that CF graphene based structure offers high TMR ∼100%, and the transport of carrier is through tunneling as there are no transmission states near Fermi level. This suggests that graphene sheet with both-side fluorination with 100% coverages acts as a perfect insulator and hence a better barrier to the carriers which is due to negligible spin down current (I↓) in both Parallel Configuration (PC) and Antiparallel Configuration (APC).

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Electrical Spin Injection into Graphene through Monolayer Hexagonal Boron Nitride

Abstract: We demonstrate electrical spin injection from a ferromagnet to a bilayer graphene

Cited by 99 publications

References 31 publications

Construction of van der Waals magnetic tunnel junction using ferromagnetic layered dichalcogenide

Construction of van der Waals magnetic tunnel junction using ferromagnetic layered dichalcogenide

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

Tuning the tunneling magnetoresistance by using fluorinated graphene in graphene based magnetic junctions

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