Spin Polarization Research Articles

Theory-driven design of local spin-state modulation at atomically dispersed iron sites for enhanced CO2 electroreduction

Herein, density functional theory (DFT) was used to guide the systematic design of highly efficient single-atom electrocatalysts to improve the kinetics of the CO2 reduction reaction (CO2RR). We present a novel class of catalysts that exhibit magnetic-proximity-induced exchange splitting (spin polarization). The design of these catalysts involved the precise modulation of d-shell energy levels at metallic sites and the subsequent alteration of the atomic/molecular orbitals of the adsorbed intermediates. To validate the effectiveness of our design strategy, we introduced neighboring nitrogen (N) doping near the Fe-N4 coordination environment, demonstrating the successful manipulation of the local spin state of the active sites. The results of the theoretical calculations align with the experimental results, with remarkable selectivity exceeding 90 % at low potentials (<-0.5 V vs. RHE) and sustained electrocatalytic activity for over 24 h. In situ characterization further revealed that a modulated local spin state led to a decrease in the occupation of the Fe 3d spin-down electronic states below the Fermi level. Concurrently, electrons migrated to the frontier antibonding orbitals of *COOH. This dual effect resulted in a lower reaction energy (ΔG), representing a thermodynamic benefit, and accelerated proton transfer to *COOH, representing a kinetic benefit, collectively enhancing the electrocatalytic process.

Cobalt Ditelluride Meets Tellurium Vacancy: An Efficient Catalyst as a Multifunctional Polysulfide Mediator toward Robust Lithium-Sulfur Batteries.

The commercialization of lithium-sulfur batteries (LSBs) faces significant challenges due to persistent issues, such as the shuttle effect of lithium polysulfides (LiPSs) and the slow kinetics of cathodic reactions. To address these limitations, this study proposes a vacancy-engineered cobalt ditelluride catalyst (v-CoTe2) supported on nitrogen-doped carbon as a sulfur host at the cathode. Density functional theory calculations and experimental results indicate that the electron configuration modulation of v-CoTe2 enhances the chemical affinity and catalytic activity toward LiPS. Specifically, v-CoTe2 can strongly interact with PSs through multisite coordination, effectively facilitating the kinetics of the LiPS redox reaction. Furthermore, the introduction of Te vacancies generates a large number of spin-polarized electrons, further enhancing the reaction kinetics of LiPS. As a result, the v-CoTe2@S cathode demonstrates high initial capacity and excellent cyclic stability, maintaining 80.4% capacity after 500 cycles at a high current rate of 3 C. Even under a high sulfur load of 6.7 mg cm-2, a high areal capacity of 6.1 mA h cm-2 is retained after 50 cycles. These findings highlight the significant potential of Te vacancies in CoTe2 as a sulfur host material for LSBs.

Asymmetries in invisible dark matter mediator production associated with tt¯ final states

In this paper, we propose two sets of different CP-sensitive observables inspired by the Higgs production in association with the top quark. We employ a dark matter simplified model that couples a scalar mediator with top quarks. The reconstruction of the kinematic variables is presented at next to leading order (NLO) accuracy for events associated with this massive scalar particle, which is assumed to be vanishing to invisible decays in a detector such as ATLAS. We build these observables by taking advantage of the similarity between the scalar coupling with the top quark and the factorization theorem in the total scattering amplitude, in order to represent the basis in which the phase space is parametrized. A twofold approach employs the direct implementation of the four-momentum phase space measure in building CP sensitive observables such as b2 for the Higgs, and the spin polarization of the top-quark decays in the narrow width approximation for the employed model. We studied the asymmetries of these distributions to test for any improvement in increasing the exclusion region for the gu33S−gu33P parameters associated with this vanishing scalar particle. We have found no significant effect in the exclusion limits by using the forward-backward asymmetry distributions and the full-shaped ones. Considering the case of an invisible mediator with mass of 10−2 GeV for a luminosity of 300 fb−1 expected at the end of Run 3, the best limits for gu33S and gu33P at NLO accuracy were obtained using the variables b˜2y^ and b2 respectively, with corresponding limits set to [−0.0425,0.0425] and [−0.83,0.83] at 68% CL. Published by the American Physical Society 2024

Spin-Polarized Antiferromagnetic Metals

Spin-polarized antiferromagnets have recently gained significant interest because they combine the advantages of both ferromagnets (spin polarization) and antiferromagnets (absence of net magnetization) for spintronics applications. In particular, spin-polarized antiferromagnetic metals can be useful as active spintronics materials because of their high electrical and thermal conductivities and their ability to host strong interactions between charge transport and magnetic spin textures. We review spin and charge transport phenomena in spin-polarized antiferromagnetic metals in which the interplay of metallic conductivity and spin-split bands offers novel practical applications and new fundamental insights into antiferromagnetism. We focus on three types of antiferromagnets: canted antiferromagnets, noncollinear antiferromagnets, and collinear altermagnets. We also discuss how the investigation of spin-polarized antiferromagnetic metals can open doors to future research directions.

Bias-induced magnetic to nonmagnetic transition in polyacene junctions

By means of the first-principles method, the bias effect on the magnetism of polyacene (n-acene) connected to gold electrodes is investigated. A magnetic to nonmagnetic transition for the polyacene (n &amp;gt; 6) is observed when the bias exceeds a critical value. The mechanism is explored as the bias-induced variation of electronic localization, which leads to the exchange of dominant mechanism for molecular magnetism from Columbic interaction between electrons to electron hopping rate. A significant enhancement of the differential conductance and suppression of current spin polarization for the molecular device are also obtained accompanied by the transition of molecular magnetism. This work proposes a feasible way to manipulate the magnetism of polyacene via electric method and reveals the relation between molecular magnetism and its conductance.

Electron spin resonance impact on the longitudinal resistance in the quantum Hall regime

The electron spin resonance impact on the longitudinal resistance in the quantum Hall regime near the integer filling factors is considered. For the odd filling factors extra spin excitons are created in the process of the microwave absorption, and the resistance increase due to the effective temperature rise. For the even filling factors in the absorption process depending on the temperature inspired spin polarization leads to transition of the spin-flip excitations to the higher energy short-lived excitations, and as a result the resistance is decreased due to effective temperature decrease.

Novel dopant-free ferromagnetic Mott-like insulator and high-energy correlated-plasmons in unconventional strongly correlated s band of low-dimensional gold

Ferromagnetic insulators and plasmons have attracted a lot of interest due to their rich fundamental science and applications. Recent research efforts have been made to find dopant-free ferromagnetic insulators and unconventional plasmons independently both in strongly correlated electron systems. However, our understanding of them is still lacking. Existing dopant-free ferromagnetic insulator materials are mostly limited to complex d- or f-systems with extremely low Curie temperature, low-symmetry structure, and strict growth conditions on specific substrates, limiting their compatibility with industrial applications. Unconventional plasmon is, on the other hand, a quasiparticle that originates from the collective excitation of correlated-charges, yet they are rarely explored, particularly in ferromagnetic insulator materials. Herewith, we present a novel, room temperature dopant-free ferromagnetic Mott-like insulator with a high-symmetry structure in unconventional strongly correlated s band of low-dimensional highly oriented single-crystal gold quantum dots (HOSG-QDs) on MgO(001). Interestingly, HOSG-QDs show new high-energy correlated-plasmons with low-plasmonics-loss. With a series of state-of-the-art experimental techniques, we find that the Mott-insulating state is tunable with surprisingly strong spin-splitting and spin polarization accompanied by strong s–s transitions, disappearance of Drude response, and generating new Mott-like gap. Supported with a series of theoretical calculations, the interplay of quantum confinement, many-body electronic correlations, and hybridizations tunes electron–electron correlations in s band and determines the ferromagnetism, Mott-like insulator, and high-energy correlated-plasmons. Our result shows a new class of room temperature dopant-free ferromagnetic Mott-like insulator and high-energy correlated-plasmons with low-loss in strongly correlated s band and opens unexplored applications of low-dimensional gold in spin field-effect transistors and plasmonics.

The role of a tantalum interlayer in enhancing the properties of Fe3O4 thin films.

High spin polarization and low resistivity of Fe3O4 at room temperature have been an appealing topic in spintronics with various promising applications. High-quality Fe3O4 thin films are a must to achieve the goals. In this report, Fe3O4 films on different substrates (SiO2/Si(100), MgO(100), and MgO/Ta/SiO2/Si(100)) were fabricated at room temperature with radio-frequency (RF) sputtering and annealed at 450 °C for 2 h. The morphological, structural, and magnetic properties of the deposited samples were characterized with atomic force microscopy, X-ray diffractometry, and vibrating sample magnetometry. The polycrystalline Fe3O4 film grown on MgO/Ta/SiO2/Si(100) presented very interesting morphology and structure characteristics. More importantly, changes in grain size and structure due to the effect of the MgO/Ta buffering layers have a strong impact on saturation magnetization and coercivity of Fe3O4 thin films compared to cases of no or just a single buffering layer.

Temperature dependence of spin transport behavior in Heusler alloy CPP-GMR

In this study, we investigate the effect of temperature on the performance of a read sensor by utilizing an atomistic model coupled with a spin transport model. Specifically, we study the temperature dependence of spin transport behavior and MR outputs in a Co2FeAl0.5Si0.5\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ ext {Co}_2\ ext {FeAl}_{0.5}\ ext {Si}_{0.5}$$\\end{document} (CFAS)(5nm)/Cu(5nm)/CFAS(5nm) trilayer with diffusive interfaces. Initially, the two-channel model of spin-dependent resistivity is used to calculate the temperature dependence of spin transport parameters which serves as essential input for the spin accumulation model. Our findings demonstrate that as the temperature increases, the spin transport parameters and magnetic properties decrease due to the influence of thermal fluctuation. At a critical temperature, where the ferromagnet transitions to a paramagnetic state, we observe zero spin polarization. Furthermore, at elevated temperatures, the spin accumulation deviates from the equilibrium value, leading to a reduction in the magnitude of spin current and spin transport parameters due to thermal effects. As a consequence, the MR ratio decreases from 65% to 20% with increasing temperature from 0 to 400 K. Our results are consistent with previous experimental measurements. This study allows to deeply understand the physical mechanism in the reader stack which can significantly benefit reader design.

Transition-Metal-Related Quantum Emitters in Wurtzite AlN and GaN.

Transition-metal centers exhibit a paramagnetic ground state in wide-bandgap semiconductors and are promising for nanophotonics and quantum information processing. Specifically, there is a growing interest in discovering prominent paramagnetic spin defects that can be manipulated using optical methods. Here, we investigate the electronic structure and magneto-optical properties of Cr and Mn substitutional centers in wurtzite AlN and GaN. We use state-of-the-art hybrid density functional theory calculations to determine level structure, stability, optical signatures, and magnetic properties of these centers. The excitation energies are calculated using the constrained occupation approach and rigorously verified with the complete active space configuration interaction approach. Our simulations of the photoluminescence spectra indicate that in AlN and in GaN are responsible for the observed narrow quantum emission near 1.2 eV. We compute the zero-field splitting (ZFS) parameters and outline an optical spin polarization protocol for and . Our results demonstrate that these centers are promising candidates for spin qubits.

Electron Spin Polarization and Memory Effect in Supramolecular Gel Exclusively From Achiral Building Blocks.

Chirality has been identified as a crucial component in achieving high spin selectivity in organic polymers and π-conjugated molecules. In particular, chiral polymers and supramolecular structures have emerged as promising candidates for spin filtering due to the chirality-induced spin selectivity (CISS) effect. However, the CISS effect in supramolecular systems has not been extensively investigated, despite its potential for applications in spintronics. In this work, for the first time, the potential applications of the CISS effect in supramolecular gel materials and shed light on its untapped possibilities have been successfully explored. The ability of supramolecular gel exclusively made from achiral building blocks to selectively filter electron's spin through the symmetry breaking has been demonstrated. Furthermore, this study shows that their spin filtering efficacy can be improved by using chiral solvents. More importantly, the CISS effect has been employed to explore a novel phenomenon referred to as the "spin memory effect", where the desired spin information is preserved by retaining the helicity even in the absence of the chiral solvent. These findings underscore the immense potential for spintronics applications that rely solely on achiral components, thereby paving the way for new possibilities in device design and functionality.

Design of spintronic devices based on adjustable half-metallicity induced by electric field in A-type antiferromagnetic bilayer NiI2

Exploring the attainment of half-metallic behavior in two-dimensional (2D) materials through external perturbations is a popular area of current research. In this work, we demonstrate, using first-principles calculations, that bilayer NiI2 (bi-NiI2) is an A-type antiferromagnetic (AFM) semiconductor with an indirect bandgap of 0.86 eV, with the most stable configuration being the AB stacking mode. Upon the application of a vertical electric field, the material transforms from its original semiconducting state into a half-metallic state. Moreover, the spin polarization reverses its orientation whenever the direction of the electric field is altered. This intriguing behavior has inspired us to design a spintronic device based on the A-type AFM bi-NiI2. By employing nonequilibrium Green's function (NEGF) combined with density functional theory (DFT) calculations, we find that the device achieves ON/OFF switching by applying vertical electric fields in parallel or anti-parallel configurations in the two leads. The device displays 100 % spin polarization in the parallel configuration (PC) scenario, driven by bias voltage or temperature differences. Utilizing either the parallel or antiparallel configuration (APC) for ON/OFF switching enables the device to exhibit tunneling magnetoresistance (TMR) of up to 1.45 × 1010 % due to bias voltage and up to 1011 % thermal TMR arising from temperature differences between the leads. These findings highlight the potential of NiI2 and A-type AFM bilayers in the design of spintronic devices.

Impact of composition on the properties of full-Heusler Ti2FexMn1-xAl alloys in spintronics

This study explores the structural, electronic, and magnetic characteristics of full-Heusler Ti2FexMn1-xAl alloys for spintronic applications. The regular Heusler structure is identified as the most stable across all x concentrations. The inverse Heusler structure exhibits half-metallic behavior with a finite energy band gap in the spin-up states, while the regular structure shows metallic behavior for both spin directions. Dirac-like points along the M→Γ direction are observed, particularly in alloys with x = 0 and 0.25 (inverse structure) and x = 0.5, 0.75, and 1 (regular structure), indicating advanced electronic properties. Magnetic analysis reveals that Ti atoms' local magnetic moments are antiparallel to those of Mn and Fe atoms. The total magnetic moment is highest for x = 1 (Ti2MnAl) and nearly zero for x = 0 (Ti2FeAl). Additionally, the inverse Heusler structure achieves 100 % spin polarization at the Fermi energy, underscoring its suitability for spintronic applications. This study highlights the potential of Ti2FexMn1-xAl alloys for future spintronic devices.

Spin dynamics of 2-DEG Rashba-Dresselhaus spin-orbit systems: Quantum propagators and semi-analytical analysis in low electron density.

Abstract The spin dynamics in space and time for Dresselhaus and Rashba spin-orbit interaction 2-DEG systems can be studied for any value of their β and α coefficients by using quantum propagators. With the development of analytical expressions for the quantum propagators and numerical solutions of the wave function, it has been possible to simulate the spin propagation in space-time and analyze the spin dynamics for different α/β ratios. In the present paper, the effects of the spin diffusion for large collision time τp, was performed by using quantum propagators for different α/β ratios. It was found that the largest degree of spin polarization is achieved when |α| = |β|.

Current-driven mechanical motion of double stranded DNA results in structural instabilities and chiral-induced-spin-selectivity of electron transport.

Chiral-induced-spin-selectivity of electron transport and its interplay with DNA's mechanical motion are explored in a double stranded DNA helix with spin-orbit-coupling. The mechanical degree of freedom is treated as a stochastic classical variable experiencing fluctuations and dissipation induced by the environment as well as force exerted by nonequilibrium, current-carrying electrons. Electronic degrees of freedom are described quantum mechanically using nonequilibrium Green's functions. Nonequilibrium Green's functions are computed along the trajectory for the classical variable taking into account dynamical, velocity dependent corrections. This mixed quantum-classical approach enables calculations of time-dependent spin-resolved currents. We showed that the electronic force may significantly modify the classical potential, which, at sufficient voltage, creates a bistable potential with a considerable effect on electronic transport. The DNA's mechanical motion has a profound effect on spin transport; it results in chiral-induced spin selectivity, increasing spin polarization of the current by 9% and also resulting in temperature-dependent current voltage characteristics. We demonstrate that the current noise measurement provides an accessible experimental means to monitor the emergence of mechanical instability in DNA motion. The spin resolved current noise also provides important dynamical information about the interplay between vibrational and spin degrees of freedom in DNA.

Chiral Split Magnon in Altermagnetic MnTe.

Altermagnetism is a newly recognized magnetic class named after the alternating spin polarizations in both real and reciprocal spaces. Like the spin splitting of electronic bands, the magnon bands in altermagnets are predicted to exhibit alternating chiral splitting. In this work, by performing inelastic neutron scattering on α-MnTe, we directly observed the altermagnetic magnon splitting. The lifted degeneracy of magnons is well explained by a symmetric-exchange origin. Further calculation based on the obtained spin-wave model demonstrates the magnons are chiral split as well. In addition, the g-wave magnetism was experimentally identified in MnTe.

Effect of substitutional Sb doping on the structural stability, half-metallicity, elastic properties, electronic properties, and magnetism of the Co₂MnSn full Heusler compound

We conducted Density Functional Theory (DFT) calculations using the full potential linearized augmented plane wave (FP-LAPW) method to modify the Fermi level by introducing Sb doping into Co2MnSn.This was done through the Generalized Gradient Approximation (GGA) and modified Becke-Johnson (mBJ-GGA) formalisms to enhance spin polarization and suggest signs of half-metallicity. For both ferromagnetic and paramagnetic phases, lattice optimization was performed to identify the stable magnetic structure. The results designate that the doped alloys are stable in a ferromagnetic phase with L21 structure. The calculated elastic constants suggest that the doped alloys meet the criteria for mechanical stability. The magnetism in these compounds is primarily due to the localized moments on the Mn and Co atoms. According to mBJ-GGA calculations, the total magnetic moment slightly increases with Sb doping. Analysis of the optical constants revealed the optoelectronic properties, confirming semiconducting behavior. Doping elements to achieve half-metallicity is demonstrated to be an effective method for discovering new materials suitable for spintronics applications.

Polarization enhancement based on holographic recording modulation in rubidium vapor

Spin polarization is an important parameter of magnetometers, and is essential for enhancing the stability and sensitivity of magnetic field measurements. The interference light field formed by the small angle interference of two right-handed circularly polarized beams remains right-handed circularly polarized, which can polarize alkali metal atoms and enable holographic recording. To analyze the effect of holographic modulation on spin polarization, we first performed holographic recordings in two cells: one containing pure 87Rb vapor, and the other containing 87Rb atoms, N2 and He, which is commonly used in atomic magnetometers. Holographic recordings from the optical field amplification and the influences of signal light detuning and temperature on the hologram were experimentally studied. The diffraction efficiency can be obtained by detecting the intensity of the diffracted beam, and the diffraction efficiency reached 5% in the 87Rb-He-N2 cell. Measurements of the spin polarization, demonstrated that holographic record modulation effectively enhanced spin polarization in the two cells, and the presence of a buffer gas contributed to spin polarization. This method increased the polarizability of the signal light to the atoms by 4.3% and is expected to achieve higher polarizability through the fine-tuning of the light field. The results show that the holographic light field may aid in further improving the sensitivity of atomic magnetometers under the premise of constant signal intensity.

Simultaneous enhancement of tritium burn efficiency and fusion power with low-tritium spin-polarized fuel

Abstract This study demonstrates that using spin-polarized deuterium-tritium (D-T) fuel with more deuterium than tritium can increase tritium burn efficiency (TBE) by at least an order of magnitude without compromising fusion power output, compared to unpolarized fuel. Although previous studies show that a low tritium fraction can enhance TBE, this strategy resulted in reduced fusion power density. The surprising improvement in TBE at fixed power reported here is due to the TBE increasing nonlinearly with decreasing tritium fraction but the fusion power density increasing roughly linearly with D-T cross section. A study is performed for an ARC-like tokamak producing 481 MW of fusion power with unpolarized 53:47 D-T fuel, finding the minimum startup tritium inventory ($I_{\mathrm{startup,min}}$) is 0.69 kg. By spin-polarizing half of the fuel and using a 60:40 D-T mix, $I_{\mathrm{startup,min}}$ is reduced to 0.08 kg, and fully spin-polarizing the fuel with a 63:37 D-T mix further reduces $I_{\mathrm{startup,min}}$ to 0.03 kg. Some ARC-like scenarios {are predicted to} achieve plasma ignition with relatively modest spin polarization. These findings indicate that, with advancements in helium divertor pumping efficiency, TBE values of approximately 10-40\% could be achieved using low-tritium-fraction and spin-polarized fuel with minimal power loss. This would dramatically lower tritium startup inventory requirements and reduce the amount of on-site tritium. More generally than just for spin-polarized fuels, {increased} plasma performance can be used to increase TBE. This strongly motivates the development of spin-polarized fuels and low-tritium-fraction operation for burning plasmas.&amp;#xD;

Electron Spin Dynamics of the Intersystem Crossing in Aminoanthraquinone Derivatives: The Spectral Telltale of Short Triplet Excited States.

We studied the excited state dynamics of two bis-amino substituted anthraquinone (AQ) derivatives, with absorption in the visible spectral region, which results from the attachment of a electron-donating group to the electron-deficient AQ chromophore. Femtosecond transient absorption spectra show that intersystem crossing (ISC) takes place in 190-320 ps, and nanosecond transient absorption spectra demonstrated an unusually short triplet state lifetime (2.06-5.43 μs) for the two AQ derivatives. Pulsed laser-excited time-resolved electron paramagnetic resonance (TREPR) spectra show an inversion of the electron spin polarization (ESP) phase pattern of the triplet state at a longer delay time after laser flash. Spectral simulations show faster decay of the Ty sublevel than the other two sublevels (τx = 15.0 μs, τy = 1.50 μs, τz = 15.0 μs); theoretical computation predicts initial overpopulation of the Ty sublevel, and rationalizes the short T1 state lifetime and the ESP inversion. Theoretical computations taking into account the electron-vibrational coupling, i.e., the Herzberg-Teller effect, successfully rationalize the TREPR experimental observations.