Perfect Spin Filtering Research Articles

Conductance and spin-filter effects of oxygen-incorporated Au, Cu, and Fe single-atom chains

We studied the spin-polarized electron transport in oxygen-incorporated Au, Cu, and Fe single-atom chains (SACs) by first-principles calculations. We first investigated the mechanism responsible for the low conductance (<1G0) of the Au and Cu SACs in an oxygen environment reported in recent experiments. We found that for the Au SACs, the low conductance plateau around 0.6G0 can be attributed to a distorted chain doped with a single oxygen atom, while the 0.1G0 conductance comes from a linear chain incorporated with an oxygen molecule and is caused by an antibonding state formed by oxygen's occupied frontier orbital with dz orbitals of adjacent Au atoms. For the Cu SACs, the conductance about 0.3G0 is ascribed to a special configuration that contains Cu and O atoms in an alternating sequence. This exhibits an even-odd conductance oscillation with an amplitude of ∼0.1G0. In contrast, for the alternating Fe-O SACs, conductance overall decreases with an increase in O atoms and it approaches nearly zero for the chain with more than four O atoms. While the Cu-O SACs behave as perfect spin filters for one spin channel due to the half metallic nature, the Fe-O SACs can serve as perfect spin filters for two spin channels depending on the polarity of the applied gate voltage.

Designing of spin-filtering devices in zigzag graphene nanoribbons heterojunctions by asymmetric hydrogenation and B-N doping

Using nonequilibrium Green's function in combination with the spin-polarized density functional theory, the spin-dependent transport properties of boron and nitrogen doped zigzag graphene nanoribbons (ZGNRs) heterojunctions with single or double edge-saturated hydrogen have been investigated. Our results show that the perfect spin-filtering effect (100%), rectifying behavior and negative differential resistance can be realized in the ZGNRs-based systems. And the corresponding physical analysis has been given.

Abnormal oscillatory conductance and strong odd–even dependence of a perfect spin-filtering effect in a carbon chain-based spintronic device

By using nonequilibrium Green's functions in combination with the density functional theory, the transport properties of a carbon chain-based spintronic device are investigated.

Negative Differential Resistance and Spin-Filtering Effects in Zigzag Graphene Nanoribbons with Nitrogen-Vacancy Defects

We explore the electronic and transport properties of zigzag graphene nanoribbons (GNRs) with nitrogen-vacancy defects by performing fully self-consistent spin-polarized density functional theory calculations combined with non-equilibrium Green's function technique. We observe robust negative differential resistance (NDR) effect in all examined molecular junctions. Through analyzing the calculated electronic structures and the bias-dependent transmission coefficients, we find that the narrow density of states of electrodes and the bias-dependent effective coupling between the central molecular orbitals and the electrode subbands are responsible for the observed NDR phenomenon. In addition, the obvious difference of the transmission spectra of two spin channels is observed in some bias ranges, which leads to the near perfect spin-filtering effect. These theoretical findings imply that GNRs with nitrogen-vacancy defects hold great potential for building molecular devices.

Surface half-metallicity of CrS thin films and perfect spin filtering and spin diode effects of CrS/ZnSe heterostructure

Recently, ferromagnetic zinc-blende Mn1−xCrxS thin films (above x = 0.5) were fabricated experimentally on ZnSe substrate, which confirmed the previous theoretical prediction of half-metallic ferromagnetism in zinc-blende CrS. Here, we theoretically reveal that both Cr- and S-terminated (001) surfaces of the CrS thin films retain the half-metallicity. The CrS/ZnSe(001) heterogeneous junction exhibits excellent spin filtering and spin diode effects, which are explained by the calculated band structure and transmission spectra. The perfect spin transport properties indicate the potential applications of half-metallic CrS in spintronic devices. All computational results are obtained by using the density functional theory combined with nonequilibrium Green's function.

Electronic and spin transport properties in zigzag silicene nanoribbons with edge protrusions

We investigate the electronic transport properties of zigzag-edged silicene nanoribbons (ZSiNRs) with one or two protrusions at the edges using the density functional theory combined with nonequilibrium Green's function method. It is found that the protrusion generally breaks down the edge state along the same edge, which carries current in the junction. For the ZSiNR having an even number of zigzag chains in its width, the protrusions can increase the conductance except for the case of two symmetric protrusions. For ZSiNRs with an odd number of zigzag chains in its width, the introduction of edge protrusions can suppress currents. We also investigate the spin-dependent transport properties of ZSiNR-based devices with antiparallel (AP) magnetism configuration. Interestingly, only non- and symmetric-protrusion models with a width of an even number of zigzag chains show a perfect spin filter effect.

Perfect Spin-Filtering in 4H-TAHDI-Based Molecular Devices: the Effect of N-Substitution

Based on the non-equilibrium Green's function formalism and spin-polarized density functional theory calculations, we investigate the spin transport properties of HDI and terahydrotetraazahexacene diimide (4H-TAHDI) with two ferromagnetic zigzag-edge graphene nanoribbon electrodes. Compared with HDI, four carbon atoms in the hexacene part of 4H-TAHDI are substituted by nitrogen atoms. The results show that the nitrogen substitution can improve significantly the spin-filtering performance and 4H-TAHDI can be used as a perfect spin filter. Our study indicates that suitable chemical substitution is a possible way to realize high-efficiency spin filters.

Transport properties of bare and hydrogenated zigzag silicene nanoribbons: Negative differential resistances and perfect spin-filtering effects

Ab initio calculations are performed to investigate the spin-polarized transport properties of the bare and hydrogenated zigzag silicene nanoribbons (ZSiNRs). The results show that the ZSiNRs with symmetric (asymmetric) edges prefer the ferromagnetic (antiferromagnetic) as their ground states with the semiconductor properties, while the accordingly antiferromagnetic (ferromagnetic) states exhibit the metallic behaviors. These facts result in a giant magnetoresistance behavior between the ferromagnetic and antiferromagnetic states in the low bias-voltage regime. Moreover, in the ferromagnetic ZSiNRs with asymmetric edges, a perfect spin-filtering effect with 100% positive electric current polarization can be achieved by altering the bias voltage. In addition, we also find that the negative differential resistances prefer the metastable states. The findings here indicate that the asymmetric and symmetric ZSiNRs are promising materials for spintronic applications.

Fluorinated boron nitride nanotube quantum dots: a spin filter.

Spin filtering requires a selective transmission of spin-polarized carriers. A perfect spin filter allows all majority (or minority) spin carriers to pass through a channel while blocking the minority (or majority) carriers. The quest for a novel low-dimensional metal-free magnetic material that would exhibit magnetism at a higher temperature with an excellent spin filtering property has been intensively pursued. Herein, using a first-principles approach, we demonstrate that the fluorinated boron nitride nanotube (F-BNNT) quantum dot, which is ferromagnetic in nature, can be used as a perfect spin filter with efficiency as high as 99.8%. Our calculation shows that the ferromagnetic spin ordering in F-BNNT is stable at a higher temperature. Comparison of the conductance value of the F-BNNT quantum dot with that of the pristine BNNT quantum dot reveals a significantly higher conductance in F-BNNT, which is in very good agreement with the experimental report (Tang, C., et al. J. Am. Chem. Soc. 2005, 127, 6552).

Designing cross-linked carbon nanotubes as perfect spin filter and spin valve

By applying nonequilibrium Green’s functions in combination with density-function theory, the spin-dependent transport properties of cross-linked carbon nanotube spintronic devices are investigated. Our calculations show that the perfect spin filtering effect with the almost 100% spin polarization, and the magnetoresistance effect with a magnetoresistance ratio larger than 104% can be observed in the device. The occurrence of the perfect spin-filtering and magnetoresistance effects in the cross-linked carbon nanotube spintronic device provides the possibility for further improving the integration level of carbon nanotube networks. Moreover, the mechanisms for these interesting phenomena are suggested.

Fine Spin Filtering Effect in Co-Phthalocyanine Molecule Induced by the Spin Polarization of Co Atom

Spintronic devices will play a very important role in future information technology. In this study, By spin-polarized density-functional theory calculations combined with the Keldysh nonequilibrium Green’s method, the effect of the spin direction of Co atom in Co- phthalocyanine molecule in modulating spin filtering effects under external biases are investigated. Here, an individual single molecule Co-phthalocyanine is sandwiched between two infinite 8-zigzag-graphene nanoribbon electrodes. we find that the spin direction of the Co atom relative to the magnetic polarization of the left and right electrodes can improve the spin filtering effect greatly. when the polarization direction of the two electrodes is antiparallel and the polarization of Co atom in the Co-phthalocyanine molecule upward, the configuration posesses almost perfectly spin-filter effect. The underlying mechanism of the perfect spin filtering action is applied.

Spin transport properties of partially edge-hydrogenated MoS2 nanoribbon heterostructure

We report ab initio calculations of electronic transport properties of heterostructure based on MoS2 nanoribbons. The heterostructure consists of edge hydrogen-passivated and non-passivated zigzag MoS2 nanoribbons (ZMoS2NR-H/ZMoS2NR). Our calculations show that the heterostructure has half-metallic behavior which is independent of the nanoribbon width. The opening of spin channels of the heterostructure depends on the matching of particular electronic orbitals in the Mo-dominated edges of ZMoS2NR-H and ZMoS2NR. Perfect spin filter effect appears at small bias voltages, and large negative differential resistance and rectifying effects are also observed in the heterostructure.

SPIN-FILTERING, RECTIFYING AND NEGATIVE DIFFERENTIAL RESISTANCE BEHAVIORS IN Co(dmit)2 MOLECULAR DEVICES WITH MONATOMIC (C, Fe, Au) ELECTRODES

Using nonequilibrium Green's functions (NEGFs) combined with the density functional theory (DFT), we study the electronic transport properties of a single molecule magnet Co ( dmit )2, which is sandwiched between two monatomic chain electrodes, and the different electrode materials carbon, iron and gold, have been considered. The results show that the electrodes play a crucial role in the spin-dependent transport of the Co ( dmit )2 molecular device, and some interesting phenomenon, such as perfect spin-filtering effect, rectifying and negative differential resistance (NDR) can be observed. We demonstrated that the magnetic Fe electrode can lead to high spin-flittering effect, and the different hybridization and alignment of energy levels between the molecule and the electrodes may be responsible for the rectification performance, and the distributions (delocalization or localization) of the frontier molecular orbitals under different bias result in the NDR behaviors. These characteristics could be used in the study of spin physics and the realization of nanospintronic devices.

The effect of a magnetic field on the spin-selective transport in double-stranded DNA

Spin-polarization in double-stranded DNA is studied in the presence of a magnetic field applied along its helix axis using the non-equilibrium Green's function method. The spin-polarization could be tuned by changing the magnetic field. In some special cases, the double-stranded DNA behaved as a perfect spin-filter. Furthermore, the dependency of the spin-polarization on the spin-orbit strength and dephasing strength is studied.

Giant magnetoresistance and perfect spin filter in silicene, germanene, and stanene

Silicene, germanene and stanene are two-dimensional topological insulators exhibiting helical edge states. We investigate global and local manipulations at the edges by exposing them to (i) a charge-density-wave order, (ii) a superconductor, (iii) an out-of-plane antiferromagnetic, and (iv) an in-plane antiferromagnetic field. We show that these perturbations affect the helical edge states in a different fashion. As a consequence one can realize quantum spin-Hall effect without edge states. In addition, these edge manipulations lead to very promising applications: a giant magnetoresistance and a perfect spin filter. We also investigate the effect of manipulations on a very few edge-sites of a topological insulator nanodisk.

Nearly perfect spin filter, spin valve and negative differential resistance effects in a Fe4-based single-molecule junction.

The spin-polarized transport in a single-molecule magnet Fe4 sandwiched between two gold electrodes is studied, using nonequilibrium Green's functions in combination with the density-functional theory. We predict that the device possesses spin filter effect (SFE), spin valve effect (SVE), and negative differential resistance (NDR) behavior. Moreover, we also find that the appropriate chemical ligand, coupling the single molecule to leads, is a key factor for manipulating spin-dependent transport. The device containing the methyl ligand behaves as a nearly perfect spin filter with efficiency approaching 100%, and the transport is dominated by transmission through the Fe4 metal center. However, in the case of phenyl ligand, the spin filter effect seems to be reduced, but the spin valve effect is significantly enhanced with a large magnetoresistance ratio, reaching 1800%. This may be attributed to the blocking effect of the phenyl ligands in mediating transport. Our findings suggest that such a multifunctional molecular device, possessing SVE, NDR and high SFE simultaneously, would be an excellent candidate for spintronics of molecular devices.

Controllable fully spin-polarized transport in a ferromagnetically doped topological insulator junction

We investigate the energy band structure and the spin-dependent transport for a normal/ferromagnetic/normal two-dimension topological insulator (TI) junction. By diagonalizing Hamiltonian for the system, the band structure shows that the edge states on two sides are coupled resulting in a gap opening due to the transverse spatial confinement. Further, the exchange field induced by magnetic impurities can also modulate the band structure with two spin degenerate bands splitting. By using the nonequilibrium Green's function method, the dependence of spin-dependent conductance and spin-polarization on the Fermi energy, the exchange field strength and the ferromagnetic TI (FTI) length are also analyzed, respectively. Interestingly, the degenerate conductance plateaus for spin-up and -down channels are broken, and both the conductances are suppressed by magnetic impurities due to the time-reversal symmetry broken and inelastic scattering. The spin-dependent conductance shows different behaviors when the Fermi energy is tuned into different ranges. Moreover, the conductance can be fully spin polarized by tuning the Fermi energy and the exchange field strength, or by tuning the Fermi energy and the FTI length. Consequently, the junction can transform from a quantum spin Hall state to a quantum anomalous Hall state, which is very important to enable dissipationless charge current for designing perfect spin filter.

Perfect spin filter and strong current polarization in carbon atomic chain with asymmetrical connecting points

The spin-dependent electron transport properties through a single-carbon atomic chain (SCAC) sandwiched between two-zigzag-graphene-nanoribbon (zGNR) electrodes are investigated by performing first-principles calculations based on the nonequilibrium Green's function (NEGF) approach in combination with spin density functional theory (DFT). Our calculations show that SCAC connecting two zGNRs with asymmetry-contacting points is a perfect spin filter in the transmission function within a large energy range. Moreover, the spin-dependent electron transmission spectra exhibit robust transport polarization characteristics and a strong current polarization behavior (almost 100%) can be found. The microscopic mechanisms are proposed for the spin-related phenomena.

Spin-filtering, giant magnetoresistance, rectifying and negative differential resistance effects in planar four-coordinate Fe complex with graphene nanoribbon electrodes.

By using the nonequilibrium Green's function formalism combined with the density functional theory, we have investigated the spin-polarized transport properties of a planar four-coordinate Fe complex sandwiched between two zigzag-edge graphene nanoribbon (ZGNR) electrodes, where the ZGNRs are modulated by external magnetic field. The results show that the system can exhibit perfect dual spin-filtering and spin-rectifying effects at a wide bias range, giant magnetoresistance effect with large magnetoresistance ratio at small bias, and obvious negative differential resistance behavior. The mechanisms are proposed for these phenomena.

Perfect spin polarization in symmetric two-terminal mesoscopic rings

Spin-polarized transport through an Aharonov–Bohm (AB) semiconductor mesoscopic ring is investigated in the presence of both the Rashba spin–orbit interaction (RSOI) and the Dresselhaus spin–orbit interaction (DSOI). The ring symmetrically bridges two input and output electrodes. Based on tight-binding model and Greenʼs function formalism, we find that for AB fluxes other than integer or half-integer multiples of the flux quanta the ring acts as a spin selective device with unit efficiency only when the difference between strengths of RSOI and DSOI is nonzero and small. Results of this study can be used to design a nonmagnetic-material-based perfect spin filter.