Spin-dependent Electron Transport 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.

Electronic transport of an extended Ising chain with competing thermal fluctuation and magnetic ordering

In this study, we investigate the behavior of spin-dependent electronic transport in a magnetic nanowire with thermal random oriented moments, connected to two similar (anti-) ferromagnetic leads. The model is based on Green’s function technique within the nearest neighbor tight-binding approach in the framework of canonical ensemble. We analyze the electronic transmission and its variance in different ordered and disordered regimes at a finite temperature in an external magnetic field. The results indicate that at nonzero temperatures, thermal fluctuation of moment orientations decreases the system’s electronic conductance, leading to a smooth conductance-energy relationship. Depending on temperature and external magnetic field values as well as Ising exchange interaction strength, the system can transit to an ordered phase. Additionally, the larger length of the interacting part affects the transmission coefficient and amplifies its variance. This study sheds light on the intricate interplay between temperature, magnetic field, and moment orientations in the context of spin-dependent electronic transport through magnetic nanowires, offering valuable insights into the usage of such systems.

Two-dimensional half-metals MSi2N4 (M = Al, Ga, In, Tl) with intrinsic p-type ferromagnetism and ultrawide bandgaps.

Intrinsic half-metallic nanomaterials with 100% spin polarization are highly demanded for next-generation spintronic devices. Here, by using first-principles calculations, we have designed a class of new two-dimensional (2D) p-type half-metals, MSi2N4 (M = Al, Ga, In and Tl), which show high mechanical, thermal and dynamic stabilities. MSi2N4 not only have ultrawide electronic bandgaps for spin-up channels in the range of 4.05 to 6.82 eV but also have large half-metallic gaps in the range of 0.75 to 1.47 eV, which are large enough to prevent the spin-flip transition. The calculated magnetic moment is 1 μB per cell, resulting from polarized N1-px/py orbitals. Moreover, MSi2N4 possess robust long-range ferromagnetic orderings with Curie temperatures in the range of 35-140 K, originating from the interplay of N1-M-N1 superexchange interactions. Furthermore, spin dependent electronic transport calculations reveal 100% spin polarization. Our results highlight new promising 2D ferromagnetic half-metals toward future spintronic applications.

Efficient spin filtering through Fe4GeTe2-based van der Waals heterostructures.

Utilizing ab initio simulations, we study the spin-dependent electronic transport characteristics within Fe4GeTe2-based van der Waals heterostructures. The electronic density of states for both free-standing and device-configured Fe4GeTe2 (F4GT) confirms its ferromagnetic metallic nature and reveals a weak interface interaction between F4GT and PtTe2 electrodes, enabling efficient spin filtering. The ballistic transport through a double-layer F4GT with a ferromagnetic configuration sandwiched between two PtTe2 electrodes is predicted to exhibit an impressive spin polarization of 97% with spin-up electrons exhibiting higher transmission probability than spin-down electrons. Moreover, we investigate the spin transport properties of Fe4GeTe2/GaTe/Fe4GeTe2 van der Waals heterostructures sandwiched between PtTe2 electrodes to explore their potential as magnetic tunnel junctions in spintronic devices. The inclusion of monolayer GaTe as a 2D semiconducting spacer between F4GT layers results in a tunnel magnetoresistance of 487% at a low bias and decreases with increasing bias voltage. Overall, our findings underscore the potential of F4GT/GaTe/F4GT heterostructures in advancing spintronic devices based on van der Waals materials.

Floquet-engineered chiral-induced spin selectivity.

The control of electron spin, crucial to the stability of matter, offers new possibilities for manipulating the properties of molecules and materials with potential applications in spintronics and chemical reactions. Recent experiments have demonstrated that electron transmission through chiral molecules depends on the electron spin orientation, a phenomenon known as chiral-induced spin selectivity (CISS). In this study, we show that CISS can be observed in achiral systems driven by an external circularly polarized laser field in the framework of Floquet engineering. By using the Floquet theory for a time-periodically driven system to investigate spin-dependent electron transport in a two-terminal setup, we demonstrate that the spin polarization can approach unity if the light intensity is sufficiently strong, the rate of dephasing is sufficiently low, and the average chemical potential of the two leads is within an appropriate range of values, which is narrow because of the high frequency of the laser field. To obtain a broader range of energies for large spin polarization, a combination of chiral molecules and light-matter interactions is considered, and the spin polarization of electrons transported through a helical molecule driven by a laser field is evaluated.

Spin-selectivity effect of G-quadruplex DNA molecules.

Chirality-induced spin selectivity has been attracting extensive interest in recent years and is demonstrated in a variety of chiral molecules, all of which arise from inherent molecular chirality. Here, we first propose a theoretical model to study the spin-dependent electron transport along guanine-quadruplex (G4) DNA molecules, connected to two nonmagnetic electrodes, by considering the molecule-electrode contact and weak spin-orbit coupling. Our results indicate that the G4-DNA molecular junctions exhibit pronounced spin-selectivity effect, and the asymmetric contact-induced external chirality, instead of the inherent molecular chirality, dominates their spin filtration efficiency. Furthermore, the spin-selectivity effect is robust against the disorder and hold in a wide range of model parameters. These results could be checked by charge transport measurements and provide an alternative way to improve the spin-selectivity effect of chiral nanodevices.

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.

Chiral-Induced Spin Selectivity in Photon-Coupled Achiral Matters.

Chiral-induced spin selectivity is a phenomenon in which electron spins are polarized as they are transported through chiral molecules, and the spin polarization depends on the handedness of the chiral molecule. In this study, we show that spin selectivity can be realized in achiral materials by strongly coupling electrons to a circularly polarized mode of an optical cavity or waveguide. Through the investigation of spin-dependent electron transport in a two-terminal setup using the nonequilibrium Green's function approach, it is found that a large spin polarization can be obtained if the rate of dephasing is sufficiently small and the average chemical potential of the two leads is within an appropriate range of values, which is narrow because of the high frequency of the optical mode. To obtain a wider range of energies for a large spin polarization, chiral molecules can be combined with light-matter interactions. To demonstrate this, the spin polarization of electrons transported through a helical molecule strongly coupled to a circularly polarized optical mode is evaluated.

First-principles investigations for the electronic and transport properties of zigzag SiC nanoribbons with Fluorine passivation/adsorption

Nanoribbons with different edge functionalization display interesting electronic properties for various device applications. It requires the necessity of exploring the novel passivating elements commensurate to various technological applications. In this direction, here we have compared the effect of H and F-passivation on the edges of zigzag SiC nanoribbons (ZSiCNR) using density functional theory based calculations. Remarkably, present study reveals that F could be used as an effective passivating element for ZSiCNR similar to widely explored H-passivations. Various possible combinations of F/H are found to have stable structural integrity for practical applications. The effect of F-adatom adsorption is also discussed which present peculiar electronic properties. The half-metallic behavior is observed to be realized via F-adsoprtion which is further confirmed with the transport calculations. The obtained negative differential resistance along the spin dependent electron transport pledges towards wide spread applications of considered ZSiCNR interacting with F.

Atomistic Modeling of Spin and Electron Dynamics in Two-Dimensional Magnets Switched by Two-Dimensional Topological Insulators

To design fast memory devices, we need material combinations that can facilitate fast read and write operations. We present a heterostructure comprising a two-dimensional (2D) magnet and a 2D topological insulator (TI) as a viable option for designing fast memory devices. We theoretically model the spin-charge dynamics between 2D magnets and 2D TIs. Using the adiabatic approximation, we combine the nonequilibrium Green's function method for spin-dependent electron transport and a time-quantified Monte Carlo method for simulating magnetization dynamics. We show that it is possible to switch a magnetic domain of a ferromagnet using the spin torque from spin-polarized edge states of a 2D TI. We show further that the switching of 2D magnets by TIs is strongly dependent on the interface exchange (${J}_{\mathrm{int}}$), and an optimal interface exchange, is required for efficient switching. Finally, we compare experimentally grown Cr compounds and show that Cr compounds with higher anisotropy (such as $\mathrm{Cr}{\mathrm{I}}_{3}$) result in a lower switching speed but a more stable magnetic order.

Bipolar spin-filtering and giant magnetoresistance effect in spin-semiconducting zigzag graphene nanoribbons.

Spintronics is one of the main topics in condensed matter physics, in which half-metallicity and giant magnetoresistance are two important objects to achieve. In this work, we study the spin dependent transport properties of zigzag graphene nanoribbons (ZGNR) with asymmetric edge hydrogenation and different magnetic configurations using the non-equilibrium Green's function method combined with density functional calculations. Our results show that when the magnetic configurations of the electrodes change from parallel to antiparallel, the currents in the tunnel junction change substantially, resulting in a high conductance state and a low conductance state, with the tunnel magnetoresistance (TMR) ratio larger than 1 × 105% achieved. In addition, in the parallel magnetic configurations, an ideal bipolar spin filtering effect is observed, making it flexible to switch the spin polarity of current by reversing the bias direction. All these features originate from the spin semiconducting behavior of the asymmetrically hydrogenated ZGNRs. The findings suggest that asymmetric edge hydrogenation provides an important way to construct multi-functional spintronic devices with ZGNRs.

Multifunctional 2D g-C4N3/MoS2 vdW Heterostructure-Based Nanodevices: Spin Filtering and Gas Sensing Properties.

Two-dimensional (2D) magnetic materials are the key to the development of the new generation in spintronics technology and engineering multifunctional devices. Herein, the electronic, spin-resolved transmission, and gas sensing properties of the 2D g-C4N3/MoS2 van der Waals (vdW) heterostructure have been investigated by using density functional theory with non-equilibrium Green's function method. First, the g-C4N3/MoS2 vdW heterostructure demonstrates ferromagnetic half-metallicity and superior adsorption capacity for gas molecules. The spin-dependent electronic transport of the g-C4N3/MoS2-based nanodevice is obviously regulated by parallel or anti-parallel spin configuration in electrodes, leading to perfect single-spin conduction behavior with a nearly 100% spin filtering efficiency, a negative differential resistance effect, and other interesting electrical transport phenomena. Moreover, g-C4N3/MoS2 exhibits directional dependency and strong transport anisotropic behavior under bias windows, indicating that the electric current propagates more easily through the vertical direction than the horizontal direction. The physical mechanisms are revealed and analyzed by presenting the bias-dependent transmission spectra in combination with the projected local device density of states. Finally, the g-C4N3/MoS2-based gas sensor is more sensitive to CO, NO, NO2, and NH3 molecules with the chemisorption type. The strong chemical adsorption leads to the formation of electrons on the local scattering center and ultimately affects the transport properties, resulting in the maximum gas sensitivity reaching 6.45 for NO at the bias of 0.8 V. This work not only reveals that the g-C4N3/MoS2 vdW heterostructure with high anisotropy, perfect spin filtering, and outstanding gas sensitivity is a promising 2D material but also provides an insight into the further application in futuristic electronic nanodevices.

Nanotherapy based on magneto-mechanochemical modulation of tumor redox state.

Magnetic nanoparticles (MNs) are typically used as contrast agents for magnetic resonance imaging or as drug carriers with a remotely controlled delivery to the tumor. However, they can also potentiate the action of anticancer drugs under the influence of applied constant magnetic (CMFs) and electromagnetic fields (EMFs). This review demonstrates the role of magneto-mechanochemical effects produced by MNs alone and loaded with anticancer agents (MNCs) in response to CMFs and EMFs for modulation of tumor redox state. The combined treatment is suggested to act by two mechanisms: spin-dependent electron transport propagates free radical chain reactions, while magnetomechanical interactions cause conformational changes in drug molecules loaded onto MNs and generate reactive oxygen species (ROS). By adjusting the parameters of CMFs and EMFs during the magneto-mechanochemical synthesis and subsequent treatment, it is possible to modulate ROS production and switch redox signaling involved in ERK1/2 and NF-κB pathways from initiation of tumor growth to inhibition. Observations of tumor volume in different animal models and treatment combinations reported a 6%-70% reduction as compared with conventional drugs. Despite these results, there is a general lack of research in magnetic nanotheranostics that link redox changes across multiple levels of organization in the tumor-bearing host. Further multidisciplinary studies with more focus on the relationship between the electron transport processes in biomolecules and their effects on the tumor-host interaction should accelerate the clinical translation of magnetic nanotheranostics. This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease Therapeutic Approaches and Drug Discovery > Emerging Technologies Nanotechnology Approaches to Biology > Nanoscale Systems in Biology.

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.

Dynamical mean-field theory for spin-dependent electron transport in spin-valve devices

We present a combination of density functional theory and dynamical mean-field theory (DMFT) for computing the electron transmission through two-terminal nanoscale devices. The method is then applied to metallic junctions presenting alternating Cu and Co layers, which exhibit spin-dependent charge transport and the giant magnetoresistance (GMR) effect. The calculations show that the coherent transmission through the $3d$ states is greatly suppressed by electron correlations. This is mainly due to the finite lifetime induced by the electron-electron interaction and is directly related to the imaginary part of the computed many-body DMFT self-energy. At the Fermi energy, where in accordance with the Fermi-liquid behavior the imaginary part of the self-energy vanishes, the suppression of the transmission is entirely due to the shifts of the energy spectrum induced by electron correlations. Based on our results, we finally suggest that the GMR measured in Cu/Co heterostructures for electrons with energies about 1 eV above the Fermi energy is a manifestation of dynamical correlation effects.

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.