Tunnel magnetoresistance of a single-molecule junction

Saffarzadeh, Alireza

doi:10.1063/1.3050347

Cited by 23 publications

(17 citation statements)

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“…In a ZGNR, a gate potential may shift the spin-up and spin-down states differently and therefore, spin filters and spin switches can be achieved without magnetic contacts. [6,19,20]. For this purpose, we have shown in Fig.…”

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confidence: 99%

A spin-filter device based on armchair graphene nanoribbons

Saffarzadeh

Farghadan

2011

Applied Physics Letters

117

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The coherent spin-polarized electron transport through a zigzag-edge graphene flake (ZGF), sandwiched between two semi-infinite armchair graphene nanoribbons, is investigated by means of Landauer-Buttiker formalism. To study the edge magnetism of the ZGF, we use the half-filled Hubbard model within the Hartree-Fock approximation. The results show that the junction acts as a spin filter with high degree of spin polarization in the absence of magnetic electrodes and external fields. By applying a gate voltage the spin-filtering efficiency of this device can be effectively controlled and the spin polarization can reach values as high as 90%.Graphene nanoribbons (GNRs) and graphene junctions are good candidates for electronic and spintronic devices due to high carrier mobility, long spin-relaxation times and lengths, and spin-filtering effect [1][2][3]. In fact, the conduction electrons in carbon-based materials can move very long distances without scattering due to their small spin-orbit coupling and low hyperfine interaction. For instance, in GNRs with zigzag edges, electronic transport is dominated by edge states which have been observed in scanning tunneling microscopy [4]. These states are expected to be spin-polarized and make zigzag-edge GNR (ZGNR) junctions attractive for nanoscale spintronic applications such as spin filters [5][6][7][8][9][10][11][12]. In order to achieve a spintronic device, it is very important to find nonmagnetic materials where a spin-polarized current can be injected and flowed without becoming depolarized. The ground state of ZGNRs has an antiferromagnetic spin configuration where the total spin (S) is zero. However, when the system has different number of A-and B-sublattice sites, the total spin of the ground state is 2S = N A − N B [13] and by appropriate designing, one can form a ferromagnetic spin configuration at the zigzag edges. Most of the previous studies on spinfiltering effects have been focused on the junctions, which consist of ZGNR electrodes.In this letter, a GNR junction which operates as a spin-filter in the absence of an external electric field is presented and the influence of edge atoms on spin transport through the junction will be examined. We also investigate the sensitivity of the spin polarization to the gate voltage to obtain a maximum value for this polarization. An interesting feature of our system is that, in spite of the previous studies, the type of electrodes in this junction is armchair-edge GNR and the central part of the system is a zigzag-edge graphene nanodisk [6,14], as shown in Fig. 1(a). In this junction, the right GNR electrode with a ribbon index n=8 has a width W R =0.86 nm, while the left electrode with a ribbon index n=33 * Electronic address: a-saffar@tpnu.ac.ir has a width W L =3.93 nm. Furthermore, the central region (nanodisk) with a trapezoidal shape consists of N C = 240 carbon atoms and produces a ferromagnetic spin configuration at its edges.We simulate the system depicted in Fig. 1(a) by use of a single-band tight-binding model an...

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confidence: 99%

A spin-filter device based on armchair graphene nanoribbons

Saffarzadeh

Farghadan

2011

Applied Physics Letters

117

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“…the left and right semi-infinite magnetic electrodes [29]. The following Lehman representation is used for the calculation of theĝ , matrix elements on the z ¼ a plane, which is the first layer of the semi-infinite electrodes, as shown in Figure 1 [37]: with…”

Section: Theoretical Methodsmentioning

confidence: 99%

“…Using density functional theory or the tightbinding model, spin-polarized transport through organic molecules coupled to magnetic contacts has recently been investigated theoretically [20][21][22][23][24][25][26][27][28][29]. The results have shown that, by changing the magnetic alignment of the contacts, one can substantially affect the electronic current in molecular devices.…”

Section: Introductionmentioning

confidence: 97%

“…The results have shown that, by changing the magnetic alignment of the contacts, one can substantially affect the electronic current in molecular devices. Using the tight-binding method, TMR values of greater than 60% have been reported for a single C 60 molecule attached to two ferromagnetic electrodes with finite cross sections [29]. The magnetization, electrical conduction, and magneto resistance (MR) of C 60 -Co nanocomposites were studied by Miwa et al [30].…”

Section: Introductionmentioning

confidence: 98%

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Tunnel magnetoresistance of a C_nBN (n = 58 and 68) molecular junction

Yaghobi

Yuonesi

2012

Molecular Physics

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This research considers a system consisting of C n BN (n ¼ 58 and 68) attached by single and multiple atoms to two ferromagnetic electrodes with finite cross sections. The effects of the contacts, the position of the doped atom, the cage type and the gate and bias voltages on the coherent spin-dependent transport was studied by applying the non-equilibrium Green's function technique. The results show that pure spin currents are obtained. Also, the tunnel magnetoresistance (TMR) can reach as high as about 60% with appropriate selection of the bias and gate voltages, the type and position of the doped atoms and the cage type. A negative TMR is observed with a change of gate voltage when B and N atoms are substituted in C 60 and C 70 molecules.

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“…For instance, a large magnetoresistance was observed in graphene nanoribbon field-effect transistors by applying a perpendicular magnetic field 9 . Most of the previous studies in spin field-effect transistors demonstrate spin filtering effect by utilizing graphene and/or organic molecules in contact with magnetic electrodes [10][11][12][13] . Interestingly, it has been shown that zigzag-shaped graphene nanoribbons and quantum dots have spin-polarized features both theoretically and experimentally [14][15][16] .…”

Section: Introductionmentioning

confidence: 99%

Generation of fully spin-polarized currents in three-terminal graphene-based transistors

Farghadan

Saffarzadeh

2015

RSC Adv.

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We propose three-terminal spin devices with graphene nanoribbons (terminals) and a graphene flake (channel) to generate a highly spin-polarized current without an external magnetic field or ferromagnetic electrodes. The Hubbard repulsion within the mean-field approximation plays the main role to separate the unpolarized electric current at the source terminal into spin-polarized currents at the drain terminals. It is shown that by modulating one of the drain voltages, a fully spin-polarized current can be generated in the other drain terminal. In addition, the geometry of the channel and the arrangement of edge atoms have significant impact on the efficiency of spin currents in the three-terminal junctions which might be utilized in generation of graphene-based spin transistors.

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Tunnel magnetoresistance of a single-molecule junction

Cited by 23 publications

References 38 publications

A spin-filter device based on armchair graphene nanoribbons

A spin-filter device based on armchair graphene nanoribbons

Tunnel magnetoresistance of a C_nBN (n = 58 and 68) molecular junction

Generation of fully spin-polarized currents in three-terminal graphene-based transistors

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Tunnel magnetoresistance of a single-molecule junction

Cited by 23 publications

References 38 publications

A spin-filter device based on armchair graphene nanoribbons

A spin-filter device based on armchair graphene nanoribbons

Tunnel magnetoresistance of a CnBN (n = 58 and 68) molecular junction

Generation of fully spin-polarized currents in three-terminal graphene-based transistors

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Tunnel magnetoresistance of a C_nBN (n = 58 and 68) molecular junction