Dual Spin Filtering Research Articles

Spin-selective transport in edge-passivated zigzag magnesium dichloride nanoribbons: Towards bipolar spin diode and spin rectification devices

In the present work, we investigate the electronic, magnetic, and spin transport properties of zigzag MgCl2 (ZMgCl2) nanoribbons with different types of edge passivation using first-principles calculations based on density functional theory and non-equilibrium Green’s function techniques. Our findings reveal that the ZMgCl2 nanoribbon with Cl edges (ClαClα) and Mg edges (MgMg) exhibits distinct properties depending on the type of passivation. Passivation with O and F on ClαClα edges transforms the nanoribbon into a magnetic semiconductor. Passivation with H and F on MgMg edges results in a semiconductor behavior, B passivation leads to a half-metal behavior, and O passivation to a magnetic semiconductor. Additionally, our transport simulations demonstrate that the ClαClα-F nanoribbon operates as a single spin filter under bias voltage. For the MgMg-B nanoribbon, the behavior varies depending on the magnetic configuration of the electrodes. In the parallel configuration, MgMg-B also functions as a single spin filter, whereas in the antiparallel configuration, it operates as a dual spin filter device. Overall, our results highlight the remarkable potential of two-dimensional MgCl2 for spintronics applications, emphasizing the influence of edge passivation on the electronic and transport properties of nanoribbons.

Electrically triggered spin reversal and precise control of spin polarization for electron transport at the single-molecule level

Different from conventional ferromagnetic methods, producing a spin-polarized current through electrical ways in spintronic devices can greatly increase operating speed, reduce power consumption, and improve device integration. Inspired by recent experimental progress on the synthesis of a heptauthrene molecule, we investigate its spin-dependent transport contacted with Au electrodes through first-principles calculations. By applying a gate voltage, the transmission can be switched between completely spin-up and spin-down polarized states, achieving an electrically controlled dual-spin filter. Furthermore, a fine tuning on the spin polarization, between 100% and −100%, can also be realized, where the transport with any ratio of spin-up to spin-down electron quantities can be realized beyond the traditional devices. The peculiar transmission spectra and their shift are found to play crucial roles, where transmission peaks distribute on both sides of the Fermi level with opposite spin components. Such a spin-polarization modulating effect is found to be robust to the molecule-electrode contacting site, indicating it is an intrinsic feature of such systems. Moreover, the dimension of the device is at the single-molecule level, suggesting great application potential.

Modulation of edge defects on dual-spin filtering in zigzag β-SiC7 nanoribbons.

The unique edge states of the zigzag β-SiC7 nanoribbons aroused our attention, and therefore, based on first-principles calculations, we investigated their spin-dependent electronic transport properties by constructing controllable defects to modulate these special edge states. Interestingly, by introducing rectangular edge defects in the SiSi and SiC edge-terminated systems, not only the spin-unpolarized is successfully converted to completely spin-polarized, but also the direction of polarization can be switched, thus enabling a dual spin filter. The analyses further reveal that the two transmission channels with opposite spins are spatially separated and that the transmission eigenstates are highly concentrated at the relative edges. The specific edge defect introduced only suppresses the transmission channel at the same edge but reserves the transmission channel at the other edge. In addition, for the CSi and CC edge-terminated systems, an additional spin-down band exists due to spin splitting in the spin-up band at EF, so that besides the original spatially separated two spin-opposite channels, an extra spin channel is distributed at the upper edge, resulting in unidirectional fully spin-polarized transport. The peculiar spatially separated edge states and excellent spin filtering properties could open up further possibilities for β-SiC7-based electronic devices in spintronics applications.

Conformational change-modulated spin transport at single-molecule level in carbon systems

Controlling the spin transport at the single-molecule level, especially without the use of ferromagnetic contacts, becomes a focus of research in spintronics. Inspired by the progress on atomic-level molecular synthesis, through first-principles calculations, we investigate the spin-dependent electronic transport of graphene nanoflakes with side-bonded functional groups, contacted by atomic carbon chain electrodes. It is found that, by rotating the functional group, the spin polarization of the transmission at the Fermi level could be switched between completely polarized and unpolarized states. Moreover, the transition between spin-up and spin-down polarized states can also be achieved, operating as a dual-spin filter. Further analysis shows that, it is the spin-dependent shift of density of states, caused by the rotation, that triggers the shift of transmission peaks, and then results in the variation of spin polarization. Such a feature is found to be robust to the length of the nanoflake and the electrode material, showing great application potential. Those findings may throw light on the development of spintronic devices.

Dual spin filtering and negative differential resistance effects in vanadium doped zigzag phosphorene nanoribbons with different edge passivations

By applying density functional theory combined with nonequilibrium Green’s function, we investigate the electronic and transport properties of V-doped zigzag phosphorene nanoribbons (ZPNRs) with different edge passivations. The results show that the electronic and transport properties of vanadium-doped ZPNRs (V-ZPNRs) can be tuned by the edge passivation types. V-ZPNRs passivated by sulfur atoms possess stronger conductivity than bared ones, and edge passivation by hydrogen and halogen (F and Cl) atoms can transform V-ZPNRs from magnetic metals to magnetic semiconductors. Moreover, due to the edge passivation by hydrogen and halogen atoms, V-ZPNRs exhibit dual spin polarizability and negative differential resistance effects. The findings provide theoretical support in modulating the electronic transport properties of ZPNRs, which may be useful in designing phosphorene-based spintronic devices.

Electrically modulated reversible dual-spin filter in zigzag β-SiC7 nanoribbons.

Compared with traditional magnetic approaches, electrical modulation of spin-polarized current can greatly reduce the energy consumption and scale of nanodevices and improve their operating speed, which has become a promising research field in spintronics. Motivated by the latest reported novel two-dimensional material β-SiC7, we employ first-principles calculations to investigate its spin-dependent electron transport with diverse edge configurations. By introducing a gate voltage, the three-terminal device can not only switch between spin-unpolarized and fully spin-polarized states, but also easily change the polarization direction, behaving as an excellent electrically modulated reversible dual-spin filter. Surprisingly, an arbitrary proportion of spin-up and spin-down electron numbers is achieved, enabling precise control of spin polarization. Analysis reveals that it is attributed to the peculiar transmission spectrum, where two broad peaks with opposite spins are located around the Fermi level and respond differently to gate voltage. They belong to the spatially separated edge states originating from the p orbitals of the edge atoms. This feature is robust to different edge configurations of β-SiC7 nanoribbons, indicating that this may be an intrinsic property of such systems, showing great potential for applications.

Length-independent multifunctional device based on penta-tetra-pentagonal molecule: a first-principles study

A length-independent, stable and perfect spin-filtering, and the coexistence of dual spin-filtering and -rectifying with a high ratio, are demonstrated in designed devices.

Electrically controlled spin reversal and spin polarization of electronic transport in nanoporous graphene nanoribbons.

Based on first-principles calculations, the spin-dependent electronic transport of nanoporous graphene nanoribbons is investigated. A three-terminal configuration is proposed, which can electronically control the spin polarization of transmission, instead of magnetic methods. By modulating the gate voltage, not only could the transmission be switched between completely spin up and spin down polarized states to realize a dual-spin filter, but also the spin polarization could be finely tuned between 100% and -100%. Any ratio of spin up to spin down transport electrons can be realized, providing more possibilities for the design of nanoelectronic devices. Further analysis shows that the transmission spectra, with two distinct transmission peaks with opposite spins around EF, are the key point, which are contributed by p orbitals. And such a phenomenon is robust to the width and length of the nanoporous graphene nanoribbons, suggesting that it is an intrinsic feature of these systems. The electrical control on spin polarization is realized in pure-carbon systems, showing great application potential.

Spin-resolved transport properties of atomic carbon chain between sawtooth zigzag-edge graphene nanoribbons electrodes

ABSTRACT We investigate the magnetic transport properties for a molecular device model constructed by a carbon atomic chain embedding in two hydrogen-passivated graphene nanoribbons (GNRs) electrodes with sawtooth zigzag edges. The spin-dependent transport simulation is carried out by the first-principles approach based on the density functional theory combing with nonequilibrium Green's function formalism. It is found that the dual spin-filtering effect with the perfect efficiency up to 100, high-performance dual-spin diode effect with the rectification ratio reaches about and obvious negative differential resistance behaviour with a peak-to-valley ratio near are numerically observed in such proposed molecular device. Particularly, a giant magnetoresistance ratio approaching is also observed, which is two orders magnitude higher than the value of a zigzag-edge GNR. These findings suggest that our proposed device has multifunction with highly effective spin-filter, spin-diode, spin-valve performance.

Multifunctionality for the nanojunction of a rotating p-phenylene vinylene molecule between graphene leads

With the multi-functional molecular device based on graphene nanoribbon being deeply studied in experiment, the zigzag-edged graphene device is still worth to investigate. Employing the ab-initio method, the spin transport properties have been studied for the nanojunctions consisting of a p-phenylene vinylene (PPV) molecule sandwiched between two-probe leads of zigzag-edged graphene nanoribbons (ZGNRs). A series of obvious electromagnetic transmission functionalities, including spin switching, negative differential resistance (NDR), dual spin-filtering, magnetoresistance and spin-diode behaviors, are numerically referred in the proposed molecular junction within spin parallel or antiparallel configurations. The performance of switching and double spin filtering can be explained by the transport spectra or total transmission pathways. Besides, the rectification effect is due to the asymmetry spatial distribution of the local density of states as well as the corresponding coupling between the PPV molecule and leads. It is expected that the designed models can be ideal candidate for future spintronic device.

B5N5 monolayer: a room-temperature light element antiferromagnetic insulator.

We demonstrate theoretically that an intrinsic antiferromagnetic phase exists in monolayer materials consisting of non-magnetic light atoms, and propose that B5N5 with a decorated bounce lattice is a thermodynamically stable two-dimensional antiferromagnetic insulator by performing state-of-the-art density functional theory calculations. The antiferromagnetic phase originates from spontaneous symmetry breaking at the nearly flat bands in the vicinity of the Fermi energy. The flat bands are formed by purely s–pz orbitals and are spin degenerate. A perpendicular electric field can remove the spin degeneracy and a prototype controllable dual spin filter with 100% spin polarization is proposed. Our proposal offers a possible two-dimensional atomically thick antiferromagnetic insulator.

Large dual spin-rectifying and high-efficiency dual spin-filtering in cyclooligomeric Mn-phthalocyanine dimer molecular junction

Abstract Based on density functional theory combined with nonequilibrium Green’s function technique, we investigate the spin-polarized transport properties of the cyclooligomeric Mn-phthalocyanine dimer and Fe-phthalocyanine dimer with carbon nanotube electrodes. The results show that the spin-polarized transport properties can be effectively tuned by changing the central transition metal atoms, and the Mn-phthalocyanine dimer system can exhibit large dual spin-rectifying and high-efficiency dual spin-filtering effects simultaneously under the [1, −1] magnetic configuration. The underlying mechanism is analyzed by spin-resolved transmission spectra, molecular projected self-consistent Hamiltonian orbitals and their spatial distribution.

Edge-modulated dual spin-filter effect in zigzag-shaped buckling Ag2S nanoribbons.

Unlike MoS2, single-layered Ag2S nanoribbons (Ag2SNRs) exhibit a nonmetal-shrouded and a zigzag-shaped buckling structure and possess two distinct edges, S- or Ag-terminated ones. By performing first principle calculations, the spin-dependent electron transport of Ag2SNRs in a ferromagnetic state has been investigated. It is found that the SS- and AgAg-terminated Ag2SNRs exhibit semi-metallic characteristics, but with opposite spin-polarized directions. And AgS-terminated ones show metallic characteristics, but with completely spin-unpolarized transmission. That is to say, all three states, i.e., spin up polarized, spin down polarized and spin unpolarized ones, could be achieved by modulating the edge geometry. Further analysis shows that, the spatial separation on edges of the energy states with different spins around EF is responsible for the switch in the three states. The system could operate as a dual spin-filter, and the direction of the spin polarization can be switched by the edge morphology. Furthermore, calculations show that such a phenomenon is robust to the width of the ribbon and strain, showing great application potential.

Characteristics of electronic and spin-independent linear conductance in conjugated aromatic polymer based molecular device

Using the non-equilibrium Green's function formalism combined with density-functional theory, we performed a theoretical research to study the electronic and spin-dependent electron transport of a molecular device constructed from a 2-TBQP, 1D-conjugated aromatic polymer(CAP) and 1D-CAP with dihedral angle being 180° sandwiched between two semiinfinite zigzag-edged graphene nanoribbon (zGNR) electrodes. Results show that the proposed 1D-CAP model exhibits an interesting linear conductive behavior, which is much larger than other two models. The intriguing linear current-voltage characteristic can be explained by the well delocalized spatial distribution of frontier orbitals and the separation of electron transmission pathways. Moreover, it's also shown that the spin-charge transport can be modulated by performing the magnetic configuration in zGNR electrodes. The proposed models show many spin related behaviors, such as single spin conductance, dual spin filter and spin-independent linear conductance. The corresponding mechanisms of the above mentioned spin-resolved results can be analyzed and discussed in terms of the spin transmission spectra and the separation of isosurfaces of spin density of these systems.

Proposal for a Dual Spin Filter Based on [VO(C3S4O)2]2–

Polynuclear magnetic molecules often present dense electronic transmission spectra with many overlapping conduction spin channels. Single-metal complexes display a sparser density of states, which in the presence of a fixed external magnetic field makes them interesting candidates for spin filtering. Here we perform a DFT study of a family of bis- and tris-dithiolate vanadium complexes sandwiched between Au(111) electrodes and demonstrate that [VO(C3S4O)2]2– can behave as a dual spin filter. This means that an external electrical stimulus can switch between the selective transmission of spin-up and spin-down carriers. By using an electrostatic gate, we show that the onset for the spin-up conductance is at a voltage Vg = −0.51 V, but a small shift to Vg = −0.63 V is capable of switching to spin-down transport. For both cases, we estimate a large low-bias conductance (approximately 2 μS at Vbias 99.5%). We conclude by commenting on the general molecular requirement...

Edge defect switched dual spin filter in zigzag hexagonal boron nitride nanoribbons.

Unlike graphene nanoribbons, zigzag monolayer hexagonal boron nitride nanoribbons (ZBNNRs) possess two distinct edges (B and N edges). Using first-principles calculations, we investigate the spin-dependent electronic transport of ZBNNRs with edge defects. It is found that the defects could make the system operate as a dual spin filter, where the direction of spin polarization is switched by the defect. Further analysis shows that the transmission eigenchannels for the opposite spins reside spatially separated on opposite edges. The defect on one edge could suppress the transmission for only one spin component, but preserve that for the other spin, resulting in a dual spin filter effect. This effect is found to be unaffected by the width of the ribbon and the length of the defect. Moreover, by constructing defects on both edges, the system exhibits two transmission peaks with opposite spins residing discretely on both sides of the Fermi level, suggesting that an electrically controlled dual spin filter based on ZBNNRs is also realizable. As controllable defects have been experimentally fabricated on monolayer boron nitride [T. Pham, A. L. Gibb, Z. Li, S. M. Gilbert, C. Song, S. G. Louie and A. Zettl, Nano Lett., 2016, 16, 7142-7147], our results may shed light on the development of B/N-based spintronic devices.

The spin-dependent transport and optoelectronic properties of the 6,6,12-graphyne-based magnetic tunnel junction devices

Abstract Using density functional theory and nonequilibrium Green's function method, we investigated the spin-dependent transport and spin-polarized optoelectronic properties of the 6,6,12-graphyne-based magnetic tunnel junction (MTJ) devices. The results show that the MTJ devices have prominent dual spin-filtering effect and large tunneling magnetoresistance (TMR); the TMR values of the MTJ devices are as high as 105%. In addition, we found that the spin-polarized photocurrents of the MTJ devices are dependent on the polarization direction of light and the magnetization directions of the electrodes. Two spin-polarized photocurrents can be realized in the MTJ devices and, if the magnetization directions of the two electrodes are antiparallel, the two light-generated spins flow in opposite directions. These interesting phenomena indicate that the 6,6,12-graphyne-based MTJ devices could be used as optoelectronic or opto-spintronic devices.

Effect of amino on spin-dependent transport through a junction of fused oligothiophenes between graphene electrodes

The influence of chemical side groups is significant in physical or chemical understanding the transport through the single molecular junction. Motivated by the recent successful fabrication and measurement of a single organic molecule sandwiched between graphene electrodes (Prins et al., 2011), here we study the spin-dependent transport properties through a junction of a fused oligothiophenes molecule embedded between two zigzag-edged graphene nanoribbon (ZGNR) electrodes. The molecule with and without an attached amino NH2 side group is considered, respectively, and external magnetic fields or FM stripes are applied onto the ZGNRs to initially orient the magnetic alignment of the electrodes for the spin-dependent consideration. By the ab initio calculations based on the density functional theory combined with nonequilibrium Green’s function formalism, we have demonstrated the remarkable difference in the spin-charge transport property between the junctions of the molecule with and without NH2 side group. In particular, the junction with side group shows more obvious NDR. In addition, it exhibits an interesting dual spin-filtering effect when the magnetic alignment in electrodes is initially antiparallel-oriented. The mechanisms of the results are revealed and discussed in terms of the spin-resolved transmission spectrum associated with the frontier molecular orbitals evolution, the molecular projected self-consistent Hamiltonian eigenvalues, and the local density of states.

Magneto-electronic and magnetic transport properties of triangular graphene quantum-dot arrays

Graphene (GN), a monolayer two-dimensional (2D) system closely arranged into a benzene ring structure by C atoms, has so far aroused considerable research interest due to its novel electronic, magnetic, mechanical and thermal properties. But 2D GN is a semimetal with zero band gap, and the lowest conduction band touches the highest valence band at Fermi level, leading to the inability to achieve the off effect in the electronic device. Therefore, many researchers are searching the solutions. A simple and feasible method is to convert 2D GN into quasi-one-dimensional (1D) graphene nanoribbons, quantum-dot arrays (QDAs) and zero-dimensional (0D) quantum-dot by tailoring it along a specific single crystallographic direction. The QDAs, due to their structural diversity, have great potential applications in future nano-integrated circuit. In this work, first-principles method based on density functional theory is used to study the magneto-electronic and magnetic transport properties of four 1D quantum-dot arrays (1D QDAs) consisting of triangular graphene nanoflakes with different linking modes. The calculated binding energy suggests that these structures are very stable, and the arrays that are linked by the bottom-side are more stable than that only by the vertex. In particular, it is found that the electronic and magnetic features are not only related to the different magnetic states, but also depend on linking modes. For example, in the non-magnetism state, different QDAs can be a metal or a narrowed band-gap semiconductor. In the ferromagnetic state, different QDAs can be half-metal materials or bipolar magnetic semiconductors with different gaps, and have greatly different magnetic moments from 1.985 to 7.994B/unit cell, reaching a difference almost as large as four times. While in the antiferromagnetic state, all QDAs are semiconductors but with different gaps. These results imply that the linking modes play a crucial role in effectively tuning the electronic and magnetic features for nanostructures. The calculated atom-projected density of states indicates that the highest valence band and the lowest conduction band are determined by the edge C atoms. The half-metallic and bipolar magnetic semiconducting behaviors presented by 1D QDA are extremely important for developing magnetic devices, which is not found in the intrinsic graphene nanoribbons. And, we also investigate the magnetic device properties based on one kind of QDA, and the single or dual spin-filtering effect with the perfect (100%) spin polarization and a rectification ratio of about 104 can be predicted. Particularly, a giant magnetoresistance over 109% is found unambiguously, which is two orders of magnitude higher than the value predicted based on the zigzag graphene nanoribbons and five orders of magnitude higher than previously reported experimental values for the MgO tunnel junction. Our results thus provide strong evidence for the effectiveness of QDAs on the magneto-electronic properties.

Spin-dependent transport properties in covalent–organic molecular device with graphene nanoribbon electrodes

Based on the first-principles method, the spin-dependent transport properties of covalent-organic molecular device embedded between two zigzag-edge graphene nanoribbon (ZGNR) electrodes have been studied. It is revealed that in the parallel (P) spin configuration of two ZGNR electrodes, the molecular device exhibits a robust spin filtering effect (up to 100%). In another case of antiparallel (AP) spin configuration, dual spin filtering, spin rectifying as well as negative differential resistance (NDR) effects were discovered. These calculated results offer useful ideas for designing high-performance ZGNR-based molecular devices.