Spin-polarized Transport Research Articles

Rotating single molecule-based devices: Single-spin switching, negative differential electrical and thermoelectric resistance

Single molecule-based devices have been one of the most candidates to realize the miniaturization of traditional electronic devices. Here we investigate the spin-polarized transport properties of an iron-complex molecule sandwiched between two ferromagnetic zigzag-edged graphene nanoribbon electrodes based on the non-equilibrium Green’s function formalism combined with the density functional theory. When the iron-complex molecule rotates, a single-spin switching effect is observed at the Fermi level, and meanwhile a perfect spin filtering effect appears in the molecular device. As the electric bias increases, an obvious negative differential electrical resistance is observed. In addition, we also find a negative differential thermoelectric resistance in the absence of the electric bias under a small molecular rotation, and the sign and magnitude of the thermally driven current can be tuned by the temperature. These theoretical findings imply that the iron-complex molecular devices have potential applications in the next-generation spin electric and thermoelectric devices.

Exploiting the Close-to-Dirac Point Shift of the Fermi Level in the Sb2Te3/Bi2Te3 Topological Insulator Heterostructure for Spin-Charge Conversion.

Properly tuning the Fermi level position in topological insulators is of vital importance to tailor their spin-polarized electronic transport and to improve the efficiency of any functional device based on them. Here, we report the full in situ metal organic chemical vapor deposition (MOCVD) and study of a highly crystalline Bi2Te3/Sb2Te3 topological insulator heterostructure on top of large area (4″) Si(111) substrates. The bottom Sb2Te3 layer serves as an ideal seed layer for the growth of highly crystalline Bi2Te3 on top, also inducing a remarkable shift of the Fermi level to place it very close to the Dirac point, as visualized by angle-resolved photoemission spectroscopy. To exploit such ideal topologically protected surface states, we fabricate the simple spin-charge converter Si(111)/Sb2Te3/Bi2Te3/Au/Co/Au and probe the spin-charge conversion (SCC) by spin pumping ferromagnetic resonance. A large SCC is measured at room temperature and is interpreted within the inverse Edelstein effect, thus resulting in a conversion efficiency of λIEEE ∼ 0.44 nm. Our results demonstrate the successful tuning of the surface Fermi level of Bi2Te3 when grown on top of Sb2Te3 with a full in situ MOCVD process, which is highly interesting in view of its future technology transfer.

Spin-polarized Majorana zero modes in proximitized superconducting penta-silicene nanoribbons

We theoretically propose penta-silicene nanoribbons (p-SiNRs) with induced p-wave superconductivity as a platform for the emergence of spin-polarized Majorana zero-modes (MZMs). The model explicitly considers the key ingredients of well-known Majorana hybrid nanowire setups: Rashba spin-orbit coupling, magnetic field perpendicular to the nanoribbon plane, and first nearest neighbor hopping with p-wave superconducting pairing. The energy spectrum of the system, as a function of chemical potential, reveals the existence of MZMs with a well-defined spin orientation localized at the opposite ends of both the top and bottom chains of the p-SiNR, associated with well-localized and nonoverlapping wave function profiles. Well-established experimental techniques enable the fabrication of highly ordered p-SiNRs, complemented by a thin lead film on top, responsible for inducing p-wave superconductivity through proximity effect. Moreover, the emergence of MZMs with explicit opposite spin orientations for some set of model parameters opens a new avenue for exploring quantum computing operations, which accounts for both MZMs and spin properties, as well as for new MZMs probe devices based on spin-polarized electronic transport mechanisms.

Spin-polarized electrical transport and circularly polarized dichroic light absorption in chiral niobium triselenide nanowire

Spin-polarized electrical transport and circularly polarized dichroic light absorption in chiral niobium triselenide nanowire

High optical spin-filtering in antiferromagnetic stanene nanoribbons induced by band bending and uniaxial strain

Non-equilibrium spin-polarized transport properties of antiferromagnetic stanene nanoribbons are theoretically studied under the combining effect of a normal electric field and linearly polarized irradiation based on the tight-binding model at room temperature. Due to the existence of spin-orbit coupling in stanene lattice, applying normal electric field leads to splitting of band degeneracy of spin-resolved energy levels in conduction and valence bands. Furthermore, unequivalent absorption of the polarized photons at two valleys which is attributed to an antiferromagnetic exchange field results in unequal spin-polarized photocurrent for spin-up and spin-down components. Interestingly, in the presence of band bending which has been induced by edge potentials, an allowable quantum efficiency occurs over a wider wavelength region of the incident light. It is especially important that the variation of an exchange magnetic field generates spin semi-conducting behavior in the bended band structure. Moreover, it is shown that optical spin-filtering effect is obtained under the simultaneous effect of uniaxial strain and narrow edge potential.

Transport Property of Wrinkled Graphene Nanoribbon Tuned by Spin-Polarized Gate Made of Vanadium-Benzene Nanowire.

A series of four-terminal V7(Bz)8-WGNR devices were established with wrinkled graphene nanoribbon (WGNR) and vanadium-benzene nanowire (V7(Bz)8). The spin-polarized V7(Bz)8 as the gate channel was placed crossing the plane, the concave (endo-positioned) and the convex (endo-positioned) surface of WGNR with different curvatures via Van der Waals interaction. The density functional theory (DFT) and nonequilibrium Green's function (NEGF) methods were adopted to calculate the transport properties of these devices at various bias voltages (VS) and gate voltages (VG), such as the conductance, spin-polarized currents, transmission spectra (TS), local density of states (LDOS), and scattering states. The results indicate that the position of V7(Bz)8 and the bending curvature of WGNR play important roles in tuning the transport properties of these four-terminal devices. A spin-polarized transport property is induced for these four-terminal devices by the spin-polarized nature of V7(Bz)8. Particularly, the down-spin channel disturbs strongly on the source-to-drain conductance of WGNR when V7(Bz)8 is endo-positioned crossing the WGNR. Our findings on the novel property of four-terminal V7(Bz)8-WGNR devices provide useful guidelines for achieving flexible graphene-based electronic nanodevices by attaching other similar multidecker metal-arene nanowires.

Giant spin-splitting and tunable spin-momentum locked transport in room temperature collinear antiferromagnetic semimetallic CrO monolayer

In this work, we present theoretical predictions of a two-dimensional collinear antiferromagnetic semimetal, CrO, which exhibits a giant spin-split band structure, spin-momentum locked transport properties, and a high Néel temperature. Specifically, CrO features two pairs of spin-polarized anisotropic Weyl points at the Fermi level. By manipulating the position of these Weyl points with strain, we demonstrate that four different antiferromagnetic spintronic states with zero net magnetic moments can be achieved, including semimetals with two spin-polarized transport channels, half-semimetals, semiconductors with two spin-polarized transport channels, and half-semiconductors. The strain-induced semiconducting state also preserves the ultra-high carrier mobility of Weyl points, and the bandgap can be easily tuned. These findings offer a good avenue in spintronics without net magnetic moment or strong spin–orbit coupling and could lead to the development of antiferromagnetic materials for spintronic applications.

Very Regular Solution to Landau–Lifshitz–Gilbert System with Spin-polarized Transport

Very Regular Solution to Landau–Lifshitz–Gilbert System with Spin-polarized Transport

Monolayer MX2 (M = Cr, Mn; X = Se, Te) with a square lattice: A ferromagnetic half-metal with high Curie temperature

Ferromagnetic half-metal materials are regarded as important materials for the spintronic devices because of the fully spin-polarized carrier transport. Here, the new two-dimensional (2D) magnetic material MX2 (M = Cr, Mn; X = Se, Te) with the square lattice is designed and studied by first-principle calculations. Molecular dynamics simulation, mechanical parameters, and phonon spectrum are used to confirm structural stability. The study found that MX2 is a ferromagnetic (FM) half-metal material with a large spin and a half-metallic gap. Based on the Heisenberg model, it was discovered that MX2 has Curie temperature well above room temperature, and the fully spin-polarized transport properties in MX2 nano-devices are ensured through the volt-ampere characteristic curves. In addition, the study found that the biaxial tensile strain has significant improvement effects on ferromagnetism. The present work develops FM half-metal materials MX2 with excellent performance, which has enormous application potential in spintronics.

Spin Transport Properties of MnBi2Te4-Based Magnetic Tunnel Junctions

The van der Waals heterojunctions, stacking of different two-dimensional materials, have opened unprecedented opportunities to explore new physics and device concepts. Here, combining the density functional theory with non-equilibrium Green's function technique, we systematically investigate the spin-polarized transport properties of van der Waals magnetic tunnel junctions (MTJs), Cu/MnBi2Te4/MnBi2Te4/Cu and Cu/MnBi2Te4/h-BN/n⋅MnBi2Te4/Cu (n = 1, 2, 3). It is found that the maximum tunnel magnetoresistance of Cu/MnBi2Te4/h-BN/3⋅MnBi2Te4/Cu MTJs can reach 162.6%, exceeding the system with only a single layer MnBi2Te4. More interestingly, our results indicate that Cu/MnBi2Te4/h-BN/n⋅MnBi2Te4/Cu (n = 2, 3) MTJs can realize the switching function, while Cu/MnBi2Te4/h-BN/3⋅MnBi2Te4/Cu MTJs exhibit the negative differential resistance. The Cu/MnBi2Te4/h-BN/3⋅MnBi2Te4/Cu in the parallel state shows a spin injection efficiency of more than 83.3%. Our theoretical findings of the transport properties will shed light on the possible experimental studies of MnBi2Te4-based van der Waals magnetic tunneling junctions.

High transport spin polarization in the van der Waals ferromagnet Fe4GeTe2

The challenging task of scaling down the size of the power saving electronic devices can be accomplished by exploiting the spin degree of freedom of the conduction electrons in van der Waals (vdW) spintronic architectures built with 2D materials. One of the key components of such a device is a near-room temperature 2D ferromagnet with good metallicity that can generate a highly spin-polarized electronic transport current. However, most of the known 2D ferromagnets have either a very low-temperature ordering, poor conductivity, or low spin polarization. In this context, the ${\mathrm{Fe}}_{n}{\mathrm{GeTe}}_{2}$ (with $n\ensuremath{\ge}3$) family of ferromagnets stand out due to their near-room temperature ferromagnetism and good metallicity. We have performed spin-resolved Andreev reflection spectroscopy on ${\mathrm{Fe}}_{4}{\mathrm{GeTe}}_{2}$ (${T}_{\mathrm{Curie}}\ensuremath{\sim}273\phantom{\rule{0.16em}{0ex}}\mathrm{K}$) and demonstrated that the ferromagnet is capable of generating a very high transport spin polarization, exceeding $50%$. This makes ${\mathrm{Fe}}_{4}{\mathrm{GeTe}}_{2}$ a strong candidate for application in all-vdW power-saving spintronic devices.

Mirroring and reversible fine-tuning of the transport spin-polarization in PC3 nanoribbons based on an electrical method

The electrical approach is favored over the conventional magnetic approach for its low energy consumption and continuously variable control of spin polarization. Inspired by the recently reported PC3 monolayer, we investigate its spin-dependent electron transmission characteristics through the first-principles calculations. The results show that the transmission peaks with opposite spin directions at the Fermi level have precisely opposite responses to the gate voltage, which leads to the system being able to alter between spin-polarized and unpolarized states, and as well as achieving any ratio between − 100 % and 100 % for spin-up and spin-down electrons. Notably, this regulation is also reversible and mirror-symmetric. Further research demonstrates that the crux lies in the particular transmission peak contributed by the edge sp2-hybridized C atoms. This study sheds new light on the potential of PC3 as a novel nanoelectronic material for spintronics applications, suggesting that it can be used to create bipolar spin filters with tunable filtering effects.

Tunable magnetic anisotropy, half-metallicity and tunneling magnetoresistance effect of 2D CrI3 in CrI3/MnGeX3 (X = Se, Te) heterostructures under normal compressive strain

The induction of half-metallicity and tunable magnetic anisotropy of CrI3 monolayers remains challenging and unstable. In this study, we demonstrate that half-metallic CrI3 can be induced in a CrI3/MnGeX3(X = Se, Te) heterostructure. Normal compressive (NC) strain can effectively control the half-metallic band gap and spin-polarized electronic transport of CrI3 in CrI3/MnGeSe3. At 6% strain, the half-metallic band gap and equilibrium tunneling magneto-resistance (TMR) increases by 25% and 220%. The results of band structure, force theorem, charge density and work function calculations show that CrI3 in CrI3/MnGeSe3 loses electrons to form a hole-conducting half-metal with in-plane easy magnetization axis, while CrI3 gains electrons in CrI3/MnGeTe3 to form an electron-conducting half-metal with out-of-plane easy magnetization axis. Heterointerfacial half-metallicity in CrI3 is intrinsic without any external physical modification, and the NC strain of a two-dimensional structure can easily be realized experimentally, paving the way for further research of spintronic devices.

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.

Magnetic Nanodevices and Spin-Transport Properties of a Two-Dimensional CrSCl Monolayer

The two-dimensional intrinsic ferromagnet $\mathrm{Cr}\mathrm{S}\mathrm{Cl}$ monolayer has considerable potential for application in the development of spintronic devices because of properties such as robust ferromagnetic ordering, large spin polarization, high Curie temperature, and high carrier mobilities. Here, we investigate the electromagnetic properties of the $\mathrm{Cr}\mathrm{S}\mathrm{Cl}$ monolayer and the spin-transport properties of some conceptual magnetic devices we construct, such as p-n-junction diodes, field-effect transistors, and phototransistors, by means of first-principles calculations. The results indicate that the p-n-junction diodes of the $\mathrm{Cr}\mathrm{S}\mathrm{Cl}$ monolayer exhibit full spin-polarized transport behavior, and both the p-n and p-i-n junctions show excellent spin-filtering behavior. The phototransistor of the $\mathrm{Cr}\mathrm{S}\mathrm{Cl}$ monolayer exhibits spin-resolved photoresponse characteristics for different wavelengths of light. Furthermore, it possesses the ability to generate a fully spin-up polarized current in the visible range. Our results provide key insights into the fundamental physical properties and the underlying transport and photoresponse mechanisms of the $\mathrm{Cr}\mathrm{S}\mathrm{Cl}$ monolayer.

Ginzburg-Landau action and polarization current in an excitonic insulator model of electronic ferroelectricity

In comparison to transport of spin polarization in ferromagnets, transport of electric polarization in ferroelectrics remains less explored. Taking an excitonic insulator model of electronic ferroelectricity as a prototypical example, we theoretically investigate the low-energy dynamics and transport of electric polarization by microscopically constructing the Ginzburg-Landau action. We show that, because of the scalar nature of the excitonic order parameter, only the longitudinal fluctuations are relevant to the transport of electric polarization. We also formulate the electric-polarization diffusion equation, in which the electric-polarization current is defined purely electronically without recourse to the lattice degrees of freedom.

Cs2KMnCl6: A possible half-metallic double perovskite for spintronics

Materials with 100% spin polarisation, high-speed conduction electrons, high Curie temperatures, and ferromagnetic ground state are known for spintronics. Double perovskites (DPs) with these features are becoming popular nowadays. Herein, introducing another halide-based DP, we determined that Cs2KMnCl6 is a robust intrinsic 3d ferromagnetic half-metal with a 4 μB magnetic moment per unit cell. It exhibits the metallic band for the spin-up configuration, enabling their smooth transport, together with a massive gap of ∼4.51 eV for the spin-down states, thus protecting it from spin–flip transitions. The calculated structural and elastic stability criteria substantiate the stability of the cubic Cs2KMnCl6 double perovskite with a F m 3 ¯ m symmetry. The 3d states of Mn mainly contribute to the robust ferromagnetism above room temperature and show Tc ∼ 534 K. The different Fermi surface topologies within the Brillouin zone establish its conducting nature for up-spin channels and favor the spin-polarized transport. Moreover, the spin-polarized dielectric constant and absorption coefficient also evidenced the half-metallic characteristics. Therefore, our findings offer a novel DP system for investigating spintronic application.

Lu doping nickel oxide thin films using sol-gel spin coated and density functional theory: optoelectronic and magnetic properties

For the first time, sol-gel spin coating was used to fabricate thin films of NiO doped with lutetium. The films were characterized to determine their crystalline structure, surface morphology, and optical properties as a function of Lu doping concentration. The investigations revealed that the Lu-doped NiO films consisted of nano-polycrystalline particles with a cubic bunsenite structure and (200) preferential orientation. Optical studies indicated that the optical band gap of pure NiO widened with low levels of Lu incorporation before narrowing with higher concentrations. The Urbach energy value for pure NiO initially decreased with 1 at. % Lu-content, from 224 meV to 190 meV, and then continuously increased to 380 meV with more Lu-level. To investigate the effects of Lu doping on the electronics, magnetic, and optical properties of NiO, first-principle computations were performed. The results showed that bulk magnetization underwent significant modifications due to a high hybridization between the Lu-f/d and Ni-d states. This study suggests that NiO doped with lutetium could be used for spin-polarized transport devices and other spin-dependent applications.

High-performance spin-filtering and spin-rectifying effects in Blatter radical-based molecular spintronic device

We design a Blatter radical-based molecular spintronic device, and investigate its spin-polarized transport properties using density functional theory and non-equilibrium Green’s function technique. High-performance spin-rectifying and spin-filtering effects are realized. The physical mechanism is explained by the spin-resolved bias voltage-dependent transmission spectra, the energy levels of the corresponding molecular projected self-consistent Hamiltonian orbitals, and their spatial distributions. The results demonstrate that the Blatter radical has great potential in the development of high-performance multifunctional molecular spintronic devices.

Electron-Spin Filter Based on Dresselhaus Spin-Orbit-Coupling Modulated Single-Layered Semiconductor Nanostructure

We theoretically investigate Dresselhaus spin-orbit coupling (SOC)-induced spin-polarized transport for electrons tunneling through single-layered semiconductor nanostructure (SLSN, InSb). A considerable electron-spin polarization is observed in this SLSN. Spin polarization ratio is associated with the electron energy and in-plane wave vector; in particular, it can be manipulated by the strain engineering or the layer thickness. Based on this SLSN, a controllable electron-spin filter is proposed for spintronics device applications.