Spin Polarization Ratio Research Articles

Homochiral Covalent Organic Frameworks with Superhelical Nanostructures Enable Efficient Chirality‐Induced Spin Selectivity

AbstractDespite significant advancements in fabricating covalent organic frameworks (COFs) with diverse morphologies, creating COFs with superhelical nanostructures remains challenging. We report here the controlled synthesis of homochiral superhelical COF nanofibers by manipulating pendent alkyl chain lengths in organic linkers. This approach yields homochiral 3D COFs 13‐OR with a 10‐fold interpenetrated diamondoid structure (R=H, Me, Et, nPr, nBu) from enantiopure 1,1′‐bi‐2‐naphthol (BINOL)‐based tetraaldehydes and tetraamine. COF‐13‐OEt exhibits macroscopic chirality as right‐handed and left‐handed superhelical fibers, whereas others adopt spherical or non‐helical morphologies. Time‐tracking shows a self‐assembly process from non‐helical strands to single‐stranded helical fibers and intertwined superhelices. Ethoxyl substituents, being of optimal size, balance solvophobic effects and intermolecular interactions, driving the formation of superhelical nanostructures, with handedness determined by BINOL chirality. The superhelical nature of these materials is evident in their chiral recognition and spin‐filter properties, showing significantly improved enantiodiscrimination in carbohydrate binding (up to six times higher enantioselectivity) and a remarkable chiral‐induced spin selectivity (CISS) effect with a 48–51 % spin polarization ratio, a feature absent in non‐helical analogs.

Spin-dependent Goos-Hänchen shift for electron in single-layered semiconductor microstructure modulated by Rashba spin–orbit coupling

We theoretically investigate Goos-Hänchen effect for electron in single-layered semiconductor microstructure (SLSM) modulated by Rashba spin–orbit coupling (SOC). Due to the SOC effect, GH displacement is obviously dependent on spins, which allows electron spins to be separated in space dimension and results in spin polarization of electrons in semiconductors. Spin polarization ratio is associated with incident energy, incident direction and in-plane wave vector, e.g., it reaches maximum at resonance, but no spin polarization effect appears at normal incidence. In particular, both magnitude and sign of spin polarization ratio are controlled by external electric field or semiconductor-layer thickness, therefore, a manipulable spatial electron-spin splitter is obtained for semiconductor spintronics device applications.

Bias-controllable temporal electron-spin splitter based on a magnetic nanostructure

Applying a bias along electronic transport direction, we theoretically investigate the control of a temporal electron-spin splitter (TESS), which can be realized experimentally by patterning a horizontally-magnetized ferromagnetic stripe on the surface of InAs/AlxIn1-xAs heterostructure. Due to the spin-field interaction, dwell time for electron in this TESS device is still spin related, even if a bias is applied. Thus, electron spins are separable in time dimension, giving rise to an obvious electron-spin polarization effect. Besides, both magnitude and sign of spin polarization ratio can be tuned by changing bias, leading to an electrically-controllable TESS as a tunable electron-spin polarized source for semiconductor spintronic device applications.

Homochiral Covalent Organic Frameworks with Superhelical Nanostructures Enable Efficient Chirality-Induced Spin Selectivity.

Despite significant advancements in fabricating covalent organic frameworks (COFs) with diverse morphologies, creating COFs with superhelical nanostructures remains challenging. We report here the controlled synthesis of homochiral superhelical COF nanofibers by manipulating pendent alkyl chain lengths in organic linkers. This approach yields homochiral 3D COFs 13-OR with a 10-fold interpenetrated diamondoid structure (R = H, Me, Et, nPr, nBu) from enantiopure 1,1'-bi-2-naphthol (BINOL)-based tetraaldehydes and tetraamine. COF-13-OEt exhibits macroscopic chirality as right-handed and left-handed superhelical fibers, whereas others adopt spherical or non-helical morphologies. Time-tracking shows a self-assembly process from non-helical strands to single-stranded helical fibers and intertwined superhelices. Ethoxyl substituents, being of optimal size, balance solvophobic effects and intermolecular interactions, driving the formation of superhelical nanostructures, with handedness determined by BINOL chirality. The superhelical nature of these materials is evident in their chiral recognition and spin-filter properties, showing significantly improved enantiodiscrimination in carbohydrate binding (up to six times higher enantioselectivity) and a remarkable chiral-induced spin selectivity (CISS) effect with a 48-51% spin polarization ratio, a feature absent in non-helical analogs.

Spatial electron-spin splitting in single-layered semiconductor microstructure modulated by Dresselhaus spin-orbit coupling

Abstract Combining theory and computation, we explore Goos-Hänchen effect for electron in single-layered semiconductor microstructure (SLSM) modulated by Dresselhaus spin-orbit coupling (SOC). GH displacement depends on electron spins thank to Dresselhaus SOC, therefore, electron spins can be separated from space domain and spin-polarized electrons into semiconductors can be realized. Both magnitude and sign of spin polarization ratio change with electron energy, in-plane wave vector, strain engineering and semiconductor-layer thickness. Spin polarization ratio approaches up to maximum at resonance, however, no electron-spin polarization occurs in the SLSM for zero in-plane wave vector. More importantly, spin polarization ratio can be manipulated by strain engineering or semiconductor-layer thickness, giving rise to a controllable spatial electron-spin splitter in the field of semiconductor spintronics.

Magnetosonic shock waves in degenerate electron–positron–ion plasma with separated spin densities

This study investigates magnetosonic shock waves in a spin-polarized three-component quantum plasma using the quantum magnetic hydrodynamic model. We explore the influence of spin effects, specifically spin magnetization current and spin pressure, on shock wave behavior. Numerical analysis of the linear dispersion relation under varying parameters such as positron imbalance, spin polarization ratio, plasma beta, quantum diffraction, and magnetic diffusivity reveals differential impacts, with diffusion exerting significant influence on the plasma frequency. Our findings highlight the sensitivity discrepancy between the real and imaginary parts of the dispersion relation. Furthermore, nonlinear behavior of magnetosonic shock waves is examined via the Korteweg–de Vries–Burgers equation, showcasing transitions between oscillatory and monotonic wave patterns based on changes in dimensionless parameters. Notably, we observe the combined effects of spin-up and spin-down positrons with spin-up and spin-down electrons on shock wave dynamics, contributing to a deeper understanding of spin-plasma interactions with implications across various fields.

Dwell time and spin polarization for electron in single ferromagnetic-stripe device modulated by spin–orbit couplings

Considering both Zeeman effect and spin–orbit coupling, we calculate dwell time for electron in single ferromagnetic-stripe device (SFSD), which can be constructed by patterning a nanosized ferromagnetic stripe on the surface of GaAs/AlxGa1-xAs heterostructure. Due to an intrinsic symmetry in the SFSD, dwell time is independent of electron spins, if only Zeeman effect is involved. However, the intrinsic symmetry is broken by spin–orbit coupling, which gives rise to spin-dependent dwell time for electron in the SFSD. As a result, electron spins can be separated in time dimension, which induces an obvious electron-spin polarization effect in the SFSD. Spin polarization ratio can be efficaciously modified by interfacial confining electric-field or strain engineering, which attributes to the dependence of effective potential felt by electron in the SFSD on spin–orbit couplings. Thus, the SFSD can act as a controllable temporal electron-spin splitter, a class of electron-spin polarized sources in semiconductor spintronics.

Half-metal Mn2GeI2 monolayer with high Curie temperature and large perpendicular magnetic anisotropy

Two-dimensional (2D) intrinsic ferromagnetic (FM) materials with high Curie temperatures (Tc), large perpendicular magnetic anisotropy (PMA), and large spin polarization are desirable for atomically thin spintronic devices. Herein, we propose a 2D intrinsic FM material Mn2GeI2 monolayer with thermodynamical stability and outstanding FM properties using first-principles calculations. Our calculations show that Mn2GeI2 monolayer is a half-metal with a spin gap of 1.76 eV, which ensures 100% spin polarization ratio at the Fermi level. Importantly, Mn2GeI2 monolayer has a large PMA energy of 2.90 meV and a high Tc of 648 K, ideal for practical applications at room temperature. Further in-depth investigation of microscopic coupling in the Mn2GeI2 monolayer reveals that the robust ferromagnetism mainly resulted from the synthetic effect of Ruderman–Kittel–Kasuya–Yosida exchange interaction between the Mn ion layers and superexchange interaction within the Mn ion layers. Our results give insights into the structure and electronic and magnetic properties of Mn2GeI2 monolayer and provide a promising candidate for 2D spintronic devices.

Covalent Organic Frameworks with Tunable Chirality for Chiral-Induced Spin Selectivity.

Chiral covalent organic frameworks (CCOFs) have attracted extensive interest for their potential applications in various enantioselective processes. However, the exploitation of chirality-induced spin selectivity (CISS) that enables a new technology for the injection of spin polarized current without the need for a permanent magnetic layer within CCOFs remains a largely untapped area of research. Here, we demonstrate that, for the first time, COFs can be an attractive platform to develop spin filter materials with efficient CISS. This facilitates the design and synthesis of a new family of Zn(salen)-based 2D CCOFs, namely, CCOFs-9-12, by imine condensation of chiral 1,2-diaminocyclohexane and tri- or tetra(salicylaldehyde) derivatives. CCOF-9, distinguished by its unique C2 symmetric "armchair" tetrasubstituted pyrene conformation, exhibits the most pronounced chirality among these materials and serves as a solid-state host, enabling the enantioselective adsorption of racemic drugs with an enantiomeric excess (ee) of up to 97%. After substituting diamagnetic zinc(II) ions for paramagnetic cobalt(II), the resulting CCOF-9-Co not only retains its high crystallinity, porosity, and exceptional chirality but also exhibits enhanced conductivity, a crucial factor for the effective observation of CISS. Magnetic conductive atomic force microscopy showed that CCOF-9-Co exhibited a remarkable CISS effect with up to an 88-94% spin polarization ratio. This phenomenon is further confirmed by the increased intensity in the magnetic circular dichroism (MCD) when CCOF-9-Co is under an external magnetic field. This work therefore shows the tremendous potential of CCOFs for controlling spin selectivity and will stimulate the creation of new types of crystalline polymers with strong CISS effects for spin filters.

Spin-polarized currents induced in antiferromagnetic polymer multilayered field-effect transistors.

A theoretical construction of an antiferromagnetic polymer multilayered field-effect transistor with polymers stretched between the source and drain contacts was undertaken. The model employed a quantum approach to the on-chain spin-charge distribution, which was self-consistently coupled with the charge distribution controlled by the gate voltage. Contrary to standard field-effect transistors, we found that the current firstly increased superlinearly with the drain voltage, then it achieved the maximum for drain voltages notably lower than the gate voltage, and after that, it decreased with the drain voltage with no saturation. Such effects were coupled with the formation of the current spin-polarization ratio, where the on-chain mobility of respective spin-polarized charges was significantly dependent on the applied drain voltage. These effects arise from competition among the antiferromagnetic coupling, the intra-site spin-dependent Coulomb interaction, and the applied drain and gate voltages, which strongly influence the on-chain spin-charge distribution, varying from an alternating spin configuration to a spin-polarized configuration at both ends of the chain. Substantial control over the magnitude of spin-polarized currents was achieved by manipulating gate and drain voltages, showcasing the feasibility of practical applications in spintronics.

The quantum exchange effects on the electromagnetic solitonic excitations in warm plasma

The phenomena related to the high energy regime in a plasma medium are studied in the framework of relativistic quantum hydrodynamics at the classical level. This theory leads to nonlinear equations even at the weak relativistic regime. These nonlinearities give rise to interesting and novel phenomena in the dynamics of the medium. Here, we consider these effects on the dynamics of a warm plasma environment. In addition, we study the effects of the exchange interaction between electrons on the dynamic of such a plasma. This interaction is a quantum mechanical effect and its strength is influenced by the spin polarization ratio of the electrons. Both the analytical and the numerical solutions are presented which are stable and bounded soliton waves. For the analytical solutions, an extended tanh approach, and for the numeric approach, the techniques of solving eigenvalue problems are applied. The behavior of the vector potential and the density under the spin polarization effects and thermal effects in terms of the speed of the wave are discussed.

Design of behavior prediction model of molybdenum disulfide magnetic tunnel junctions using deep networks

Magnetic tunnel junctions (MTJ) are widely used in spintronics development owing to their high scalability and minimal power consumption. However, analyzing the electrical and magnetic behaviors of MTJ in real-time applications is challenging. In this study, an MTJ based on molybdenum disulfide (MoS2) is designed, and a novel deep Elman neural behavior prediction model is developed to analyze its behavior. MoS2 acts as a tunnel barrier in the proposed model, whereas iron oxide (Fe3O4) acts as a ferromagnetic electrode. The interface between Fe3O4 and MoS2 in the MTJ improves the spin polarization and tunnel magnetoresistance ratio. Herein, the performance parameters of the MTJ are used as inputs for the developed prediction model, which analyzes the magnetic and electrical properties of the MTJ using prediction parameters. The spin currents in the parallel and antiparallel configurations are also determined. The designed model is implemented using MATLAB and validated by comparing simulation and experimental results. Moreover, a maximum resistivity of 91 Ω is attained at a temperature of 300 K for the proposed model. At 120 K, under a positive bias, the proposed model achieves a TMR ratio of 0.936. Under negative bias, the maximum TMR ratio attained by the proposed model is 0.817.

Propagation of ion-acoustic wave and its fractal representations in spin polarized electron plasma

Propagation of small-amplitude quantum ion-acoustic waves and its fractal representations is investigated in an electron-ion quantum plasma with separated spin electrons in the framework of the KdV and EKdV equations derived using reductive perturbation technique. These two equations are transformed into planar dynamical systems by using suitable traveling wave transformation. Qualitatively different phase portraits of these two systems are drawn with their respective Sagdeev’s pseudopotential curves and surface plots. Distinct orbits in the phase portraits give rise to distinct wave solutions. Periodic and superperiodic wave solutions are investigated numerically and solitary wave solutions are derived analytically. The effect of parameters such as Mach number, direction cosine, spin polarization and frequency ratio on these wave solutions are presented. For instance, it is seen that the spin density polarization ratio has an impressive effect on the amplitude of the wave solution, while the frequency ratio has no effect on its amplitude. Also, we have provided a physical explanation for our finding. Further, the dynamical features of the original system and reconstructed system using fractal interpolation function are investigated under the external forcing term. Chaotic and quasiperiodic phenomena are observed for different initial conditions. The results may help to better understand the degenerate electron gas that exists in dense astrophysical bodies.

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.

Electron-spin polarization effect in Rashba spin-orbit coupling modulated single-layered semiconductor nanostructure

Nanothick semiconductors can grow orderly along a desired direction with the help of modern materials growth technology such as molecular beam epitaxy, which allows researchers to fabricate the so-called layered semiconductor nanostructure (LSN) experimentally. Owing to the structure inversion symmetry broken by the layered form in the LSN, the electron spins interact tightly with its momentums, in the literature referred to as the spin-orbit coupling (SOC) effect, which can be modulated well by the interfacial confining electric field or the stain engineering. These significant SOC effects can effectively eliminate the spin degeneracy of the electrons in semiconductor materials, induce the spin splitting phenomenon at the zero magnetic field and generate the electron-spin polarization in the semiconductors. In recent years, the spin-polarized transport for electrons in the LSN has attracted a lot of research interests, which is because of itself scientific importance and potential serving as spin polarized sources in the research field of semiconductor spintronics. Adopting the theoretical analysis combined with the numerical calculation, we investigate the spin-polarized transport induced by the Rashba-type SOC effect for electrons in a single-layered semiconductor nanostructure (SLSN)-InSb. The present research is to explore the new way of generating and manipulating spin current in semiconductor materials without any magnetic field, and focuses on developing new electron-spin filter for semiconductor spintronics device applications. The improved transfer matrix method (ITMM) is exploited to exactly solve Schrödinger equation for an electron in the SLSN-InSb device, which allows us to calculate the spin-dependent transmission coefficient and the spin polarization ratio. Owing to a strong Rashba-type SOC, a considerable electron-spin polarization effect appears in the SLSN-InSb device. Because of the effective potential experienced by the electrons in the SLSN-InSb device, the spin polarization ratio is associated with the electron energy and the in-plane wave vector. In particular, the spin polarization ratio can be manipulated effectively by an externally-applied electric field or the semiconductor-layer thickness, owing to the dependence of the effective potential felt by the electrons in the SLSN-InSb device on the electric field or the layer thickness. Therefore, such an SLSN-InSb device can be used as a controllable electron-spin filter acting as a manipulable spin-polarized source for the research area of semiconductor spintronics.

Bilayer hexagonal structure MnN2 nanosheets with room-temperature ferromagnetic half-metal behavior and a tunable electronic structure.

Two-dimensional (2D) layered materials have atomically thin thickness and outstanding physical properties, attracting intensive research in the past year. As one of these materials, a 2D magnet is an ideal platform for fundamental physics research and magnetic device development. Recently, a non-MoS2-type geometry was found to be more favorable in 2D transition-metal dinitrides. In this work, driven by this new configuration, we perform a comprehensive first-principles study on the bilayer hexagonal structure of 2D manganese dinitrides. Our results show that 2D MnN2 is a ferromagnetic half-metal at its ground state with 100% spin-polarization ratio at the Fermi energy level. The phonon spectrum calculation and ab initio molecular dynamics simulation show that the 2D MnN2 crystal has a high thermodynamic stability and its 2D lattice can be retained at room-temperature. Monte Carlo simulations based on the Heisenberg model predict a Curie temperature of over 563 K and its electronic properties can be regulated by biaxial strain. The half-metallic states are mainly contributed by Mn d orbitals, and the magnetic exchange of the system mainly comes from the Mn-N-Mn super-exchange. The p-d orbital hybridization will provide a small antiparallel magnetic moment of N atoms, and the p-orbital dangling bond can be eliminated by oxidation to enhance the total magnetic moment of the system. The study of magnetic anisotropy energy indicates that the easy magnetization axis is in-plane and hybridization between Mn dyz and dz2 orbitals gives the largest magnetic anisotropy contribution. In view of these results, we consider that novel 2D MnN2 is one of the most promising two-dimensional materials for nano-spintronic applications.

Spin-polarized currents through a triangle quantum dot junction driven by voltage and temperature gradient

Using the Green's function method in Hubbard model we investigate the spin-polarized currents in a triangle Quantum dot (TQD) connected to normal metal electrodes (M/TQD/M system) in the presence of Coulomb interaction. The spin-dependent currents generated by a voltage or temperature gradient in the M/TQD/M system. Results show that in both voltage-driven and temperature-driven cases the M/TQD/M system can generate spin-polarized currents with nonlinear behavior. Also, 100% current spin polarization (SP) ratio can be observed only in temperature-driven case. Besides, the spin-dependent currents and SP ratio can be interestingly controlled with the QD on-site energy, dots' level detuning factor and spin polarization factor. These results may be useful to design future spin-thermoelectric devices based on QDs.

Controllable Spin Filtering by δ-Doping for Electrons in Magnetically and Electrically Modulated Semiconductor Nanostructure

In this paper, we theoretically investigate how to control spin filtering via a [Formula: see text]-doping for electrons in a magnetically and electrically modulated semiconductor nanostructure (MEMSN), which can be realized by patterning a ferromagnetic (FM) stripe and a Schottky-metal (SM) stripe on top and bottom of GaAs/AlxGa[Formula: see text]As heterostructure in experiments, respectively. A considerable spin filtering effect still exists because of spin–orbit coupling (SOC), even if a [Formula: see text]-doping is included. Moreover, spin polarization ratio can be manipulated by [Formula: see text]-doping, which may lead to a structurally-controllable electron-spin filter for semiconductor spintronics.

Intercalated chiral-molecular 2D superlattice for spintronics

Solid-state spintronic devices are energy-efficient for data storage and energy harvesting. This field is revolutionized by the discovery of giant magnetoresistance. Recently, Qian et al. fabricated an intercalated chiral-molecular two-dimensional superlattice that exhibits highly efficient chiral-induced spin selectivity. They demonstrated a tunneling magnetoresistance ratio of >300% and a spin polarization ratio of >60%, which opens up promising future applications in spintronic devices.

Rashba Spin-Orbit-Coupling Based Electron-Spin Filter in Double-Layered Semiconductor Nanostructure

Based on a double-layered semiconductor nanostructure (DLSN)-InSb/GaSb, we propose a controllable electron-spin filter for spintronics device applications. Electron-spin polarization is induced by Rashba spin-orbit coupling inside the DLSN. Both magnitude and sign of spin polarization ratio can be manipulated by externally-applied electric field or the semiconductor-layer thickness.