Spin-dependent Electronic Transport Properties Research Articles

Dual spin filtering and dual spin diode through a zigzag silicene nanoribbon

In this study, we investigate the spin-dependent electron transport properties of a zigzag silicene nanoribbon (ZSiNR) by using spin-polarized density functional theory and the non-equilibrium Green’s function method. The results show that such a ZSiNR with an FM configuration exists the perfect dual spin filtering and dual spin diode effects when the bias voltage was applied. These phenomena still exist in ZSiNRs with different widths. As the ribbon width increases, the progressively smaller bias voltage is required to trigger a polarized current. Therefore, such a ZSiNR in FM configuration is a good candidate for spintronic devices.

Ultrahigh tunneling magnetoresistance ratios in the sandwich-structured full MXene Cr2NO2/Ti2CO2/Cr2NO2 van der Waals heterojunction

In this study, the structure, magnetism, energy-band, and spin-dependent electron transport properties of the Cr2NO2/Ti2CO2/Cr2NO2 magnetic tunnel junction (MTJ) were investigated using a combination of density functional theory and non-equilibrium Green’s function methods. The calculation band structures indicate that Cr2NO2 MXene is an “ideal” half-metal with a magnetic moment of 5.00 μB. Ti2CO2 MXene is an indirect band-gap semiconductor, and the Cr2NO2/Ti2CO2-stacked heterojunction reserve 100 % spin polarization because of the weak Van der Waals interface interaction. For the equilibrium state of the most stable Cr2NO2/Ti2CO2/Cr2NO2 MTJ, the total transmission coefficient for parallel configuration is about eleven orders of magnitude larger than that for anti-parallel configuration. An ultrahigh tunneling magnetoresistance (TMR) ratio of 1.92×1013\\% can be detected. For the non-equilibrium state, our calculation results show that the Cr2NO2/Ti2CO2/Cr2NO2 MTJ has a good transport performance when bias voltage ranges from 0 V to 0.1 V. The minimum TMR ratio of 7.51×1012% is detected at the bias voltage of 0.09 V, which can be considered as an excellent TMR ratio. Therefore, the Cr2NO2/Ti2CO2/Cr2NO2 MTJ is an excellent candidate for spintronic device application.

Modulating the electronic transport properties of zigzag phosphorene nanoribbons through the coupling with the chromium triiodide molecules

Based on density functional theory (DFT) and non-equilibrium Green's function (NEGF) method, we have investigated spin-dependent electronic transport properties of zigzag phosphorene nanoribbons (ZPNRs) coupled with chromium triiodide (CrI3) molecules. Three different adsorption models have been considered: CrI3 molecule is placed on ZPNR surface (C-type), and CrI3 molecule is lateral adsorbed on the edge of ZPNR with its molecule panel vertical (V-type) or parallel (P-type). We discovered that ZPNR's electrical transport clearly displays spin polarization, owing to the coupling between ZPNR and CrI3 molecules. And spin-polarization is tightly dependent on the absorbing manners. Moreover, the negative differential resistance (NDR) characteristics can be observed from current-voltage curves and modulated by absorbing molecules. Furthermore, we also discovered that CrI3 is vertically adsorbed on the surface of the ZPNRs has a better spin-polarization efficiency than the other two cases.

A controllable spin flip and filter in zigzag graphene nanoribbons with triangular defect

Based on the recursive Green-function method together with Landauer-Büttiker formalism, we theoretically study the controllable spin-dependent electron transport properties by using zigzag graphene nanoribbons (ZGNRs) with triangular nanoconstrictions in the presence of the ferromagnetic strips and spatial modulation of Rashba spin-orbit coupling (RSOC). In this structure, the peaks of spin-flip and spin-conserved conductance can be modulated by the strength of RSOC and exchange magnetic field. The distribution of the local density of states (LDOS) around triangular nanoconstrictions is predicted. The spin filtering effect of ZGNRs with triangular and rectangular nanoconstrictions are compared by spin conductance from left (L) to right (R) lead and R to L lead, respectively. The results might be useful in designing a bidirectional spin converter and spin filter with the modulation of the multi-parameter.

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.

Large magnetoresistance and spin-polarized photocurrent in Mn2.25Co0.75Ga0.5Sn0.5/MgO/Mn2.25Co0.75Ga0.5Sn0.5 magnetic tunnel junctions

With the development of information storage devices with high density, low power consumption and multi-means regulation, magnetic tunnel junctions (MTJs) with completely spin polarized materials as electrodes have attracted much attention. Heusler alloy Mn2.25Co0.75Ga0.5Sn0.5(MCGS) is a recently fabricated spin gapless semiconductor with 100 % spin polarization and high Curie temperature of 725 K. Here, the spin-dependent electronic transport and photoelectric properties of MCGS/MgO/MCGS MTJs are investigated systematically by density functional theory and non-equilibrium Green's function method. It is found that the MCGS/MgO/MCGS MTJs with four different terminations all present high tunnel magnetoresistance (TMR) and the maximum TMR is up to 6.51 × 106 %. The TMR value can be reduced and switched between positive and negative values by applying bias voltage, which can be used to designed magnetic logic devices. Furthermore, perfect spin injection efficiency can be obtained in the MCGS/MgO/MCGS MTJs and the switch of the spin channel can be controlled by the magnetization configuration of the ferromagnetic electrodes. Moreover, nearly 100 % spin-polarized photocurrent can be obtained by tailoring the polarization angle and photon energy of polarized light. The linearly polarized light is more favorable than circularly polarized light to generate high spin-polarized photocurrent. These results provide a theoretical guidance for designing the spin and optical tunable spintronic devices.

Trans-polyacetylene based organic spin valve for a multifunctional spin-based device: A first principle analysis

Carbon-based materials are the promising candidates for the design of multifunctional spintronic devices, owing to their fascinating inherent attributes such as the ballistic transport nature, long spin coherence time, etc. Here, we report the spin-dependent electron transport properties of a trans-polyacetylene channel sandwiched between two semi-infinite hydrogen-passivated zigzag graphene nanoribbon (ZGNR) electrodes within the framework of spin-polarized density functional theory (DFT) and non-equilibrium Green's function (NEGF) formalisms. The proposed device exhibits an excellent spin-dependent transport behavior within the bias window of [-0.5 V, 0.5 V]. In parallel configuration (PC), the device offers an ideal spin filtration efficiency of almost 100% within the bias range of [-0.4 V, 0.4 V], and in antiparallel configuration (APC), it exhibits negative differential resistance (NDR), dual-spin rectification, and dual-spin filtration effects. Also, a high tunnel magnetoresistance (TMR) of 1.2× 10 5 % is achieved. To validate the aforementioned effects, the transmission spectra along with the area enclosed by the curve, eigenvalues, eigenstates, and quantum conductance have also been analyzed. In addition, the impact of hybridization and torsion defects on the spin-dependent transport phenomenon through trans-polyacetylene has been investigated. Furthermore, the modelled device is observed to exhibit the spin Seebeck effect in PC under the influence of temperature gradient. The proposed device may stand as a good contender for various spintronic and spin caloritronic applications. • First principle based analysis of a trans-polyacetylene based multifunctional spin-based device. • The device displays a perfect spin filtration efficiency and dual rectification effects. • A high tunnel magnetoresistance (TMR) of 1.2× 10 5 % is achieved. • Thermal Spin Seebeck and spin filtering effects are observed in the proposed model. • A potential candidate in the field of spintronic and spin caloritronic applications.

Giant tunneling magnetoresistance and electroresistance in α−In2Se3 -based van der Waals multiferroic tunnel junctions

In the multiferroic tunnel junction (MFTJ) composed of ferromagnetic and ferroelectric materials, the tunneling electroresistance (TER) coexists with the tunneling magnetoresistance (TMR), making it an ideal platform for designing multifunctional electronic devices. Recently, the rapid development of van der Waals (vdW) materials opened up a new avenue of MFTJ due to their atomic thickness and significance in miniaturizing device sizes. Here by employing the nonequilibrium Green's function combined with density-functional theory, we systemically study the spin-dependent electronic transport properties of ${\mathrm{Fe}}_{3}{\mathrm{GeTe}}_{2}$ (FGT)/bilayer $\ensuremath{\alpha}\ensuremath{-}{\mathrm{In}}_{2}{\mathrm{Se}}_{3}$ (BIS)/FGT vdW MFTJs. We find that the MFTJ can form multiple nonvolatile resistance states by altering the polarization orientation of the ferroelectric barrier BIS and the magnetization alignment of the two ferromagnetic FGT electrodes, with a maximum TMR (TER) ratio up to $1.1\ifmmode\times\else\texttimes\fi{}{10}^{7}$% (744%). The TER ratio can be further increased to 1868% by using left and right symmetrical copper electrodes. More interestingly, the perfect spin filtering effect can be realized in our MFTJs and the spin current can be controlled by the sign of bias voltages, suggesting a promising route for spin valves that can flexibly manipulate spin currents. Our results demonstrate that giant TMR, large TER, as well as a tunable spin filter can coexist in one system, and that the feasible tunability of such kind of vdW MFTJs is beneficial in designing next-generation logic and memory devices.

Manipulation of Magnetic Properties and Magnetoresistance in Co/Cu/γ′-Fe4N/Mica Flexible Spin Valves via External Mechanical Strains

The strain-tailored magnetic and electronic transport properties in flexible spin valves (SPVs) have attracted attention due to their practical applications in flexible spintronic devices. Here, magnetic and spin-dependent electronic transport properties of Co/Cu/γ′-Fe4N/mica flexible SPVs are investigated. The strain-induced change ratio of magnetoresistance (MR) is 49% in Co(4.8 nm)/Cu(7.5 nm)/γ′-Fe4N(11.0 nm) flexible SPVs. The magnetic properties of Co(4.8 nm)/Cu(7.5 nm)/γ′-Fe4N(7.9 nm) flexible SPVs show mechanical stability at bending strains. The magnetic properties of flexible SPVs did not deteriorate after 100 times of bending and 60 h of bending. As the Co layer thickness decreases from 7.2 to 2.4 nm, the sign of MR changes from negative to positive. A negative MR appears due to the opposite scattering spin asymmetry coefficients between Co/Cu and γ′-Fe4N/Cu interfaces. A positive MR arises from the same scattering spin asymmetry coefficients at Co/Cu and γ′-Fe4N/Cu interfaces or magnetization misalignments between Co and γ′-Fe4N layers. Additionally, the MR is a combination of an anisotropy magnetoresistance and a giant magnetoresistance effect, which has been confirmed by MR–H curves with different measurement configurations (Hin-plane∥I, Hin-plane⊥I and Hout-of-plane⊥I) and M–H curves. The M–H curves show that the magnetization of γ′-Fe4N reverses before that of the Co layer.

Strain modulation on the spin transport properties of PTB junctions with MoC2 electrodes.

Based on MoC2 nanoribbons and poly-(terphenylene-butadiynylene) (PTB) molecules, we designed MoC2-PTB molecular spintronic devices and investigated their spin-dependent electron transport properties by using spin-polarized density functional theory and the non-equilibrium Green's function method. As a typical MXene material, it is found that the magnetic contribution of MoC2 nanoribbons mainly comes from the delocalized 3d electron of edge Mo atoms. Owing to the obvious spin-splitting near the Fermi level of the MoC2 nanoribbon electrode, the spin states can be effectively injected into the central scattering region under an external bias voltage. In addition, we also studied the effects of z-axis strain on the spin transport properties of the PTB molecular device, where the strain was controlled within the range of -9% to 9%. Under a compressed strain, spin current increases obviously, and the spin-filtering efficiency (SFE) decreases slightly. Nevertheless, under a tensile strain, we found that the SFE increases but spin current decreases. Moreover, z-axis strain can induce a negative differential resistance (NDR) effect at a high bias point. This work would expand the potential applications of new two-dimensional (2D) materials in the field of molecular spintronic devices.

Barrier-dependent electronic transport properties in two-dimensional MnBi2Te4-based van der Waals magnetic tunnel junctions

Tunneling magnetoresistance (TMR) and spin filtering effects in the magnetic tunnel junctions (MTJs) have drawn much attention for potential spintronic applications based on magnetic manipulation of electric transport. However, the traditional MTJs cannot meet the demand for rapid miniaturization of electronic components. Thus, van der Waals (vdW) MTJs with a few atomic layers stacked vertically are ideal candidates for atomic scale devices. In this work, by employing the non-equilibrium Green's function combined with density-functional theory, we systemically study the spin-dependent electronic transport properties across MnBi2Te4 (MBT)-based vdW MTJs with three typical barrier layers, i.e., monolayer hexagonal boron nitride (h-BN), monolayer graphene, and vacuum. By using graphite as the electrode of these junctions, we find that a high TMR ratio up to 4000% and almost 100% spin filtering ratio are realized in MBT|h-BN|MBT MTJ at low bias voltages. Moreover, a remarkable negative differential resistance effect is observed in MBT|h-BN|MBT and MBT|Graphene|MBT junctions. The observed barrier-dependent quantum transport phenomenon is explained by the transmission coefficient. Our unique design of these vdW structures reasonably overcomes the bottleneck of current leakage and avoids the interface contact issues and paves the way for the exploration of spintronics devices with better performance.

Modulating the spin-dependent electronic structures and transport properties of zigzag $$\upalpha $$-2 graphyne nanoribbons by boron doping

We investigated the electronic structure and spin-dependent transport properties of zigzag $$\upalpha $$ -2 graphyne nanoribbons (Z $$\upalpha $$ -2GYNRs) with boron (B) atomic doping by using first-principle non-equilibrium Green’s function method. We observed a spin-polarized semi-metallic electronic structure with an acetylenic (sp hybridized) carbon at the edge which is substituted by boron. We also calculated the spin-dependent transport properties and observed both unidirectional and bidirectional spin-filtering effects. Our results demonstrated boron substitution as an effective method for modulating the spin-dependent electronic property of the Z $$\upalpha $$ -2GYNRs. This work would provide a new scheme for designing graphyne-based spintronics devices.

Spin-dependent rare-earth-based MgPr2X4 (X = S, Se) spinels investigations for spintronic and sustainable energy systems applications

In this paper, density functional theory (DFT) calculations are performed to investigate the spin-dependent mechanical, electronic, magnetic, optical, and thermal transport properties of rare-earth-based chalcogenides MgPr2X4 (X = S, Se) spinels. The mechanical properties are obtained by employing the modified Perdew-Burke-Ernzerhof generalized gradient approximation (PBEsol GGA). Also, the modified Becke and Johnson (mBJ) potential is engaged in examining the electronic, magnetic, optical, and transport properties. Structural stability in the ferromagnetic (FM) phase is confirmed by calculating the energy difference between the FM and non-magnetic states. Besides, the formation energies are computed for thermodynamic stability. The strong hybridization near the Fermi level comes from chalcogenides 2p-states and f-states of rare-earth metals, which results in the total magnetic moments. The in-depth optical properties are evaluated in terms of dielectric constant and refraction. Lastly, electronic thermal coefficients, such as Seebeck coefficient, electrical and thermal conductivity, and power factor, are also probed and suggested studied spinels as promising sustainable energy materials.

Theoretical investigation of spin-dependent electron transport properties of dibromobenzene based positional isomers

Understanding the spin-dependent electron transport through a single molecular junction will provide in-depth knowledge to construct efficient molecular spintronic devices. The electron transport in such junction highly depends upon the structure of the molecule. The Density Functional Theory (DFT) combined with Non-Equilibrium Green's Function (NEGF) utilized to investigate the spin-dependent electron transport properties of positional isomers namely 4,6‐dibromobenzene‐1,3‐dithiol; 2,4‐dibromobenzene‐1,3‐dithiol and 2,5-dibromobenzene-1,3-dithiol. We have calculated several parameters such as the density of states, current–voltage characteristic, magnetoresistance effect etc. of these molecular junctions to understand the nature of electron transport. The projected density of states of the molecule and the total density of states shows that these molecules have good coupling with the electrode. Under the applied bias, we observed a variation of spin up and spin down transmission which leads to magnetoresistance effect in these molecular junctions. Among these molecules, the 2,5-dibromobenzene-1,3-thiol molecular junction shows a higher magnetoresistance effect than 4,6‐dibromobenzene‐1,3‐dithiol and 2,4‐dibromobenzene‐1,3‐dithiol. Hence, 2,5-dibromobenzene-1,3-thiol can be a good candidate for spintronic applications.

Thermally driven pure spin current through an interacting quantum dot

We study spin-dependent electron transport properties of a thermally driven interacting quantum dot. When an external magnetic field is applied to the quantum dot, the effective transmissions of spin-up and spin-down electrons are separated from each other and have a perfect mirror symmetry with respect to the incident energy at a certain gate voltage. A pure spin current can be induced in the system and modulated by a magnetic field. Under certain magnetic field strengths, a larger pure spin current can be obtained at gate voltages with the values in a range, not just at a specific voltage. These results indicate that the system can be worked as a pure spin current generator.

Topological spintronics in a polyacetylene molecule device

Using the Su–Schrieffer–Heeger Hamiltonian and exploiting the Green’s function method in the framework of the Landauer–Büttiker formalism, the topological and spin dependent electron transport properties of a trans polyacetylene molecule are studied. It is found that molecules with the intracell single carbon–carbon bonding and the even number of monomers in their chains have two edge states and possess topological properties though their Hamiltonians do not respect the chiral symmetry. A perpendicular exchange magnetic field and two perpendicular and transverse electric fields are used to induce and manipulate the quantum spin dependent electron transport properties. The exchange field induces the spin polarization in different electron energy regions which are expanded by stronger exchange fields. Therefore this proposed device works as a perfect spin filter. The spin polarization can be manipulated by applying the perpendicular electric field and remains robust against the transverse electric field variations.

Spin dependent electronic transport properties of zigzag black phosphorene nanojunctions induced by H, Li, O, Co asymmetric edge saturations

Two-dimensional (2D) material of few-layer black phosphorus (BP) has recently attracted extensive interest owing to its tunable band gap and high carrier mobility. We investigate the electronic transport properties of zigzag black phosphorene nanoribbons (ZBPNRs) with asymmetric H, Li, O and Co edge saturations by employing the density functional theory in combination with the non-equilibrium Green's function. The computational results forecast that different types of saturated atoms at both edge of ribbons mainly contribute to the electronic transport properties of molecular junctions. The metal edge saturation of Co atom is used to the one edge of ZBPNR which can induce an identical electronic transport property. Interestingly, the negative differential resistance (NDR) phenomena can be observed in our proposed ZBPNR junctions with an analysis of internal physical mechanism. Our theoretical results could support the possibility of potential applications to design 2D electronic devices based on the material of BP in future.

Effect of the linkage modes of thiolated ethynyl groups on the spin-dependent electronic transport properties in transition metal porphyrin molecular junctions

Using density functional theory and nonequilibrium Green’s function method, the spin-dependent electronic transport properties of six transition metal porphyrin molecules (VP, CrP, MnP, FeP, CoP, and NiP), which are linked to gold electrodes through the thiolated ethynyl groups, are investigated. Two different linkage modes (beta linkage and meso linkage) of the substituted ethynyl groups on the porphyrin macrocycle are considered. The results show that the linkage mode of ethynyl groups plays an important role on the spin transport properties of the molecular junctions and the beta linkage is more favorable for the spin filtering efficiency of current than the meso linkages. The spin-up and spin-down energy levels show the different evolutions which is responsible for the difference of spin filtering efficiency between the two linkage modes. The computational results of total current show that the meso-linked molecular junctions have the better conductive performances than the beta-linked ones which may be caused by the different electronic transport paths.

Spin-Dependent Electronic and Thermoelectric Transport Properties for a Sawtoothlike Graphene Nanoribbon Coupled to Two Ferromagnetic Leads

The spin-dependent electronic transport and thermoelectric properties for a sawtoothlike graphene nanoribbon between two ferromagnetic leads with parallel or antiparallel magnetic moments are investigated theoretically. Both Christmas-tree graphene nanoribbon and tree-saw graphene nanoribbon have been considered to exemplify the effect of the chirality. By using ab initio calculations combined with a non-equilibrium Green’s function method, we obtain the important result that these sawtoothlike graphene nanoribbon junctions, regardless of their chirality, can exhibit giant charge and spin Seebeck coefficients as well as high thermoelectric efficiency at room temperature by putting ferromagnetic stripes or magnetic fields on the nanoribbons. Specifically, large $$|S_\mathrm{C}|\,(\sim 5.8~\hbox {mV/K})$$, $$|S_\mathrm{S}|(\sim 1.8~\hbox {mV/K})$$, charge figure of merit $$ZT_\mathrm{C}$$ and spin figure of merit $$ZT_\mathrm{S}(\sim 20)$$ were found in these sawtoothlike graphene nanoribbon junctions. In addition, negative differential resistance and spin filtering were also realized in these sawtoothlike graphene nanoribbon junctions. The maximum of spin filtering efficiency can be up to 100%. Our studies suggest that sawtoothlike graphene nanoribbon junctions are suitable for use as highly efficient spin caloritronics at room temperature.

Designing of spin filter devices based on zigzag zinc oxide nanoribbon modified by edge defect**Project supported by the National Natural Science Foundation of China (Grant Nos. 61664008 and 11604286) and the Scientific Technological Innovation Team of Yan’an City, China (Grant No. 2017CXTD-01).

The spin-dependent electronic transport properties of a zigzag zinc oxide (ZnO) nanoribbon are studied by using density functional theory with non-equilibrium Green’s functions. We calculate the spin-polarized band structure, projected density of states, Bloch states, and transmission spectrum of the ZnO nanoribbon. It is determined that all Bloch states are located at the edge of the ZnO nanoribbon. The spin-up transmission eigenchannels are contributed from Zn 4s orbital, whereas the spin-down transmission eigenchannels are contributed from Zn 4s and O 2p orbitals. By analyzing the current–voltage curves for the opposite spins of the ZnO nanoribbon device, negative differential resistance (NDR) and spin filter effect are observed. Moreover, by constructing the ZnO nanoribbon modified by the Zn-edge defect, the spin-up current is severely suppressed because of the destruction of the spin-up transmission eigenchannels. However, the spin-down current is preserved, thus resulting in the perfect spin filter effect. Our results indicate that the ZnO nanoribbon modulated by the edge defect is a practical design for a spin filter.