Spin Polarization Research Articles

Current-in-plane spin polarization and magnetoresistance in a chiral device

Current-in-plane spin polarization and magnetoresistance in a chiral device

Spin injection from a magnetically near-compensated state in GdFeCo and inverse spin Hall effect in electron-hole compensated metal YH2.

Rare-earth-transition-metal (RE-TM) ferrimagnets are excellent materials for spin encode/decode operations via spin transport in nonmagnetic regions. This superior performance stems from two key factors. First, the antiferromagnetic coupling between RE4f and TM3d sublattices reduces both the spin-transfer-torque switching time and inter-device magnetic-coupling. Second, the RE-TM ferrimagnets function as spin injectors/ejectors, with the TM3d sublattice solely responsible for carrier spin polarization (p), similar to conventional ferromagnetic metals. We performed spin transport experiments using the sign change of p in RE-TM, which exhibits a positive value above the magnetization compensation temperature and a negative value below it. We measured temperature dependencies of the transverse resistances (RT) of electron-hole compensated metal YH2under out-of-plane spin-polarized current injection/ejection from GdFeCo (Gd:Fe:Co=25:66:9). The abrupt change in loop polarity of the out-of-plane field dependence of RT in YH2between 290 and 300 K, which aligns with the out-of-field curve of the polar Kerr rotation in GdFeCo electrodes, strongly suggests that the observed RT results from the inverse spin Hall effect (ISHE) in YH2. We analytically formulated ISHE in terms of the electron and hole spin currents injected from the spin sources, enabling regression analysis to assess the spin transport characteristics of a GdFeCo/YH2/GdFeCo magnetic double heterostructure. To explain the observed Hall voltages, enhancements in both the spin diffusion length of YH2and the spin injection efficiency are necessary.&#xD.

Creating Spin Channels in SrCoO3 through Trigonal-to-Cubic Structural Transformation for Enhanced Oxygen Evolution/Reduction Reactions.

Oxygen evolution and reduction reactions (OER and ORR) play crucial roles in energy conversion processes such as water splitting and air batteries, where spin dynamics inherently influence their efficiency. However, the specific contribution of spin has yet to be fully understood. In this study, we intentionally introduce a spin channel through the transformation of trigonal antiferromagnetic SrCoO2.5 into cubic ferromagnetic SrCoO3, aiming to deepen our understanding of spin dynamics in catalytic reactions. Based on the results from spherical-aberration-corrected microscopy, synchrotron absorption spectra, magnetic characterizations, and density functional theory calculations, it is revealed that surface electron transfer is predominantly governed by local geometric structures, while the presence of the spin channel significantly enhances the bulk transport of spin-polarized electrons, particularly under high current densities where surface electron transfer is no longer the limiting factor. The overpotential for OER is reduced by at least 70 mV at 150 mA cm-2 due to the enhanced conductivity from spin-polarized electrons facilitated by spin channels, with an expectation of even more significant reductions at higher current densities. This work provides a clearer picture of the role of spin in oxygen-involved electrocatalysis, providing critical insights for the design of more efficient catalytic systems in practical applications.

Hyperon Production in Bi + Bi Collisions at the Nuclotron-Based Ion Collider Facility and Angular Dependence of Hyperon Spin Polarization

The strange baryon production in Bi + Bi collisions at sNN=9.0 GeV is studied using the PHSD transport model. Hyperon and anti-hyperon yields, transverse momentum spectra, and rapidity spectra are calculated, and their centrality dependence and the effect of rapidity and transverse momentum cuts are studied. The rapidity distributions for Λ¯, Ξ, Ξ¯ baryons are found to be systematically narrower than for Λs. The pT slope parameters for anti-hyperons vary more with centrality than those for hyperons. Restricting the accepted rapidity range to |y|<1 increases the slope parameters by 13–30 MeV, depending on the centrality class and the hyperon mass. Hydrodynamic velocity and vorticity fields are calculated, and the formation of two oppositely rotating vortex rings moving in opposite directions along the collision axis is found. The hyperon spin polarization induced by the medium vorticity within the thermodynamic approach is calculated, and the dependence of the polarization on the transverse momentum and rapidity cuts and on the centrality selection is analyzed. The cuts have stronger effect on the polarization of Λ and Ξ hyperons than on the corresponding anti-hyperons. The polarization signal is maximal for the centrality class, 60–70%. We show that, for the considered hyperon polarization mechanism, the structure of the vorticity field makes an imprint on the polarization signal as a function of the azimuthal angle in the transverse momentum plane, ϕH, cosϕH=px/pT. For particles with positive longitudinal momentum, pz>0, the polarization increases with cosϕH, while for particles with pz<0 it decreases.

Theoretical studies on the scattering of e± off the C2H2 molecule

Abstract By employing previous models [15,18], we report the differential, integrated elastic, inelastic, total (elastic+inelastic), viscosity and momentum transfer cross sections of e±- C2H2 collision dynamics, for the energy range of 1 eV-1 MeV. This report also incorporates Sherman spin polarization function and total ionization cross section. This work provides the first comprehensive study of electron/positron scattering from C2H2 over such a wide energy range. A complex optical model potential (OMP) has been used to represent the projectile-atom interaction. Relativistic Dirac equation has been solved, to get phase-shifts, needed for the calculations of scattering observables, using OMP. Our results are compared with the existing experimental data and theoretical calculations.

Magnetic proximity-induced anomalous Hall effect in 2D CrOCl/Pt heterostructure

Two-dimensional (2D) van der Waals antiferromagnetic (AFM) materials boast exceptional properties for spintronics, including high spin-wave speeds and negligible stray fields. Their layer-by-layer assembly into heterostructures enables the exploration of next-generation spintronic devices. However, most 2D AFM materials are semiconductors or insulators. Thus, magneto-transport, a key segment of spintronics, is difficult to obtain especially at low temperatures. Herein, we report the observation of anomalous Hall effect (AHE) in 2D CrOCl/Pt bilayer heterostructure. Magneto-transport measurements supported by density functional theory calculations reveal that the appearance of AHE is generated by spin polarization in Pt due to the magnetic proximity effect. In addition, it is demonstrated that the magnetic easy-axis changes from the z-axis to the xy-plane at the interface of the heterostructure. Our work sheds light on the magneto-transport properties of 2D CrOCl and its potential in emerging spintronic devices.

Unlocking the potential of photoexcited molecular electron spins for room temperature quantum information processing

Abstract Future information processing technologies like quantum memory devices have the potential to store and transfer quantum states to enable quantum computing and networking. A central consideration in practical applications for such devices is the nature of the light-matter interface which determines the storage state density and efficiency. Here, we employ an organic radical, α,γ-bisdiphenylene-β-phenylallyl doped into an o-terphenyl host to explore the potential for using tuneable and high-performance molecular media in microwave-based quantum applications. We demonstrate that this radical system exhibits millisecond-long spin-lattice relaxation and microsecond-long phase memory times at room temperature, while also having the capability to generate an oscillating spin-polarized state using a co-dissolved photo-activated tetraphenylporphyrin moiety, all enabled by using a viscous liquid host. This latest system builds upon collective wisdom from previous molecules-for-quantum literature by combining careful host matrix selection, with dynamical decoupling, and photoexcited triplet-radical spin polarisation to realise a versatile and robust quantum spin medium.

Study of magnetic field error suppression methods based on atomic parameters of cell in atomic co-magnetometer rotation measurement

Abstract We propose a new model for magnetic field errors based on the rotation measurement of the K-Rb-$^{21}{\rm{Ne}}$ co-magnetometer, considering the density ratio and spin collisions. The spin polarization characteristics of different alkali metal density ratios were analyzed by creating five cells with different density ratios, and the correctness of the magnetic field error model was verified experimentally. Moreover, the effects of five different alkali metal density ratios of cells on the sensitivity, long-term stability and magnetic field error suppression of the K-Rb-$^{21}{\rm{Ne}}$ co-magnetometer were investigated experimentally. When the density ratio is 1:107, there can be the optimal magnetic field error suppression effect, sensitivity and long-term stability. According to the derived magnetic field error equation, the magnetic noise error of the K-Rb-$^{21}{\rm{Ne}}$ co-magnetometer with an optimized density ratio is reduced by nearly 5 times from 260$^{\circ}$/h/nT to 56.5$^{\circ}$/h/nT, the sensitivity is improved from 2.9$\times$10$^{-5}$ $^{\circ}$/s/Hz$^{1/2}$ to 7.0$\times$10$^{-6}$ $^{\circ}$/s/Hz$^{1/2}$ at 1 Hz, and the long-term stability Allan variance over two hours is improved from 1.9$\times$10$^{-2}$ $^{\circ}$/h to 8.9$\times$10$^{-3}$ $^{\circ}$/h. This result provides a theoretical basis for designing the parameters of the K-Rb-$^{21}{\rm{Ne}}$ co-magnetometer cell.

Observation of Highly Spin-Polarized Dangling Bond Surface States in Rare-Earth Pnictide Tellurides.

To generate and manipulate spin-polarized electronic states in solids are crucial for modern spintronics. The textbook routes employ quantum well states or Shockley/topological type surface states whose spin degeneracy is lifted by strong spin-orbit coupling and inversion symmetry breaking at the surface/interface. The resultant spin polarization is usually truncated because of the intertwining between multiple orbitals. Here a unique type of surface states is realized, namely, dangling bond surface states in a family of ternary rare-earth pnictide tellurides RePnTe (Re = La, Gd, Ce; Pn = Sb, Bi), with robust band structure and sizeable spin splitting. Spin and angle-resolved photoemission spectroscopy measurements reveal high spin polarization and distinct spin-momentum locking texture, which, according to the theoretical analysis, arise from local site asymmetry and surface-purified spin-orbital texture. The work extends the so-called "hidden spin polarization" from the bulk to the surface, presenting an intriguing spin-orbital-momentum-layer locking phenomenon, which may shed lights on potential spintronic applications.

Substantially Enhanced Spin Polarization in Epitaxial CrTe2 Quantum Films.

2D van der Waals (vdW) magnets, which extend to the monolayer (ML) limit, are rapidly gaining prominence in logic applications for low-power electronics. To improve the performance of spintronic devices, such as vdW magnetic tunnel junctions, a large effective spin polarization of valence electrons is highly desired. Despite its considerable significance, direct probe of spin polarization in these 2D magnets has not been extensively explored. Here, using 2D vdW ferromagnet of CrTe2 as a prototype, the spin degrees of freedom in the thin films are directly probed using Mott polarimetry. The electronic band of 50 ML CrTe2 thin film, spanning the Brillouin zone, exhibits pronounced spin-splitting with polarization peaking at 7.9% along the out-of-plane direction. Surprisingly, atomic-layer-dependent spin-resolved measurements show a significantly enhanced spin polarization in a 3 ML CrTe2 film, achieving 23.4% polarization even in the absence of an external magnetic field. The demonstrated correlation between spin polarization and film thickness highlights the pivotal influence of perpendicular magnetic anisotropy, interlayer interactions, and itinerant behavior on these properties, as corroborated by theoretical analysis. This groundbreaking experimental verification of intrinsic effective spin polarization in CrTe2 ultrathin films marks a significant advance in establishing 2D ferromagnetic atomic layers as a promising platform for innovative vdW-based spintronic devices.

Electronic Structure, Elasticity, Magnetism of Mn2XIn (X = Fe, Co) Full Heusler Compounds under biaxial strain: First-Principles Calculations

Abstract The electronic structure, elasticity, and magnetic properties of the Mn2XIn (X = Fe, Co) full-Heusler compounds are comprehensively investigated via first-principles calculations. The calculated elastic constants indicate that both Mn2FeIn and Mn2CoIn possess ductility. At the optimal lattice constants, the magnetic moments are found to be 1.40 μB/f.u for Mn2FeIn and 1.69 μB/f.u for Mn2CoIn. Under the biaxial strain ranging from -2% to 5%, Mn2FeIn demonstrates a remarkable variation in the spin polarization, spanning from -2% to 74%, positioning it as a promising candidate for applications in spintronic devices. Analysis of the electronic structure reveals that the change in spin polarization under strain is due to the shift of the spin-down states at the Fermi surface. Additionally, under biaxial strain, the magnetic anisotropy of Mn2FeIn undergoes a transition of easy-axis direction. Utilizing second-order perturbation theory and electronic structure analysis, the variation in magnetic anisotropy with strain can be attributed to changes of d-orbital states near the Fermi surface.

Investigations of Mechanisms Leading to Capacity Differences in Li/Na/K-Ion Batteries with Conversion-Type Transition-Metal Sulfides Anodes.

Conversion-type transition-metal sulfides (CT-TMSs) have been extensively studied as the anode of Li/Na/K-ion batteries due to their high theoretical capacity. An issue with the use of the material in the battery is that a large capacity difference is commonly observed. However, the underlying mechanism leading to the problem is still unknown. Here, the large capacity difference mechanisms of CT-TMSs anodes in the Li/Na/K-ion storage are elucidated, which arises from the difference in conversion degree and size of conversion products. Specifically, the increase in ionic radius will cause the increase in insertion-reaction ion diffuse energy barrier and conversion-reaction Gibbs free energies of phase transformation to decrease reaction kinetics, which causes a decrease in conversion degree and an increase in size of conversion products, thus leading to reduction in capacity. The increase in size and the decrease in the amount of conversion products inevitably reduce the amount of spin-polarized electrons injection into Fe and corresponding ions storage amount into sulfides during the ion-electron decoupling storage, thus reducing the capacity. The research clarifies the capacity difference mechanisms of CT-TMSs anodes in Li/Na/K storage, providing valuable insights for designing Li/Na/K storage high-capacity anodes.

First principle atomistic modelling of magnetic tunnel junction (MTJ) to enhance its tunnel magneto-resistance (TMR) ratio

Abstract This paper investigates the impact of electrode materials on the Tunnel Magneto-Resistance (TMR) ratio of Magnetic Tunnel Junction (MTJ) device. Four different structures of MTJ have been simulated by using cobalt (Co), Nickel (Ni), Iron (Fe) and two alloy materials of nickel-iron (NiFe) and cobalt-iron (CoFe). These materials have been used as ferromagnetic electrodes. Mulliken population and transmission spectrum observed in both parallel and antiparallel configurations of these devices to understand the spin transport properties and Tunnel Magneto-Resistance (TMR) ratio has been estimated. The first principal study was performed based on density function theory (DFT) and Non-equilibrium Green’s Function (NEGF) computational methods using the QuantumATK simulation tool to study properties such as band structure, the density of states (DOS), Spin Transfer Torque (STT), I-V characteristics and TMR. This study explores how different electrode materials affect the Tunnel Magneto-Resistance (TMR) ratio in Magnetic Tunnel Junction (MTJ) devices. With these results, it is observed that cobalt-based MTJ devices (that is Co-MgO-Fe and CoFe-MgO-CoFe) exhibit higher TMR ratio as compared to Nickel- and Iron-based MTJ devices (that is NiFe-MgO-NiFe and Ni-MgO-Fe). As Cobalt has a high spin polarization this property makes it suitable for use in spintronics devices like MTJs, where the manipulation of electron spins is essential for data storage and information processing. These findings can be employed to improve the performance characteristics of the MTJ-based Random Access Memory (MRAM) in the field of spintronics.

Spin polarization effect on linear polarization of photon emission following resonant electron capture of lithiumlike ions

Spin polarization effect on linear polarization of photon emission following resonant electron capture of lithiumlike ions

Magnetically Aligned Grains as a Ubiquitous Source of Spin-polarized Electrons and Chiral-symmetry-breaking Agents

The unique biosignature of life on Earth is the homochirality of organic compounds, such as amino acids, proteins, and sugars. High-energy spin-polarized (spinup or spindown) electrons (SPEs) from the β decay of radioactive nuclei have been proposed as a source of symmetry breaking, leading to homochirality; however, their exact role is much debated. Here, we propose magnetically aligned dust grains as a new source of SPEs, due to the photoemission of electrons having aligned spins by the Barnett effect. For the interstellar UV radiation field of strength G UV, we find that the SPE emission rate is ΓpeSPE∼10−14GUV electrons per second per H, the fraction of spin-polarized to total photoelectrons is ∼10%, and the SPE yield (photoelectron number per UV photon) can reach ∼1%, using the modern theory of grain alignment. SPEs emitted from aligned grains could play an important role in chiral-induced spin-selectivity-driven reduction chemistry in the icy grain mantles, producing an enantiomer excess of chiral molecules formed on the grain mantle. Finally, we suggest magnetically aligned grains could directly impact the enantio-selectivity through the chiral-induced spin-selective adsorption effect and exchange interaction. We estimate the disalignment of electron spins and depolarization by elastic scattering using the Mott theory and find that these effects are negligible for low-energy SPEs, so that the spins of SPEs remain well aligned during their journey through dust grains and the gas. Our proposed mechanism might explain the chiral asymmetry of prebiotic molecules detected in numerous comets, asteroids, and meteorites.

DFT calculations with and without spin polarization of the adsorption and decomposition of NCO and OCN on the Ag(110) surface

The adsorption of C, N, O, CO, CN, NCO and OCN, as well as the decomposition of NCO and OCN on the Ag(110) surface were studied using the density functional theory (DFT) with and without spin polarization combined with the periodic slab model, at a 0.25 ML coverage. Adsorption energy, preferred adsorption site, structural parameters, diffusion barrier of each species were determined. Work function and dipole moment changes of the Ag(110) surface allowed us to determine the direction of the charge transfer. We analyzed the interaction between the adsorbate and the surface, in the framework of the Local density of states (LDOS). Our results have revealed that the C, N and O atoms were stable on the top and hollow sites. The CN, NCO and OCN molecules bind strongly with the Ag(110) surface. While, the CO molecule weakly adsorbs on the Ag(110) surface. We found that the NCO and OCN thermochemical decomposition on the Ag(110) surface is not favorable. The CI-NEB calculations have also confirmed that the NCO and OCN decomposition on the Ag(110) surface was endothermic.

Influence of atomic substitution on the structural stability and half-metallicity of Fe2-xCrxCoSi (x = 0 to 1) alloys

Bulk Fe2-xCrxCoSi (x = 0, 0.25, 0.5, 0.75, and 1) Heusler alloys have been prepared by arc melting method. Alloys with 0.0 ≤ x ≤ 0.75 show a highly ordered phase pure XA structure. However, 17 % of an impurity (A15 phase) was detected in the alloy with x = 1. The saturation magnetization (Ms) and Curie temperature (TC) decreased linearly with an increase in Cr content for alloys with x ≤ 0.75. Ms measured at 5 K followed the Slater–Pauling rule for half-metals. Ab initio calculations with the GGA + U approach revealed that spin polarization (P) increased with an increase in Cr and eventually reached 100 % for the alloys with x = 0.5. Though Fe-Co disorder affects P, it is still high (>98 %) for alloys with x ≥ 0.5. Despite the smaller bandgap (0.61 eV) of Fe1.5Cr0.5CoSi than FeCrCoSi (0.91 eV), it has higher Ms, elevated TC, and 100 % P. These factors, coupled with the challenges associated with obtaining phase pure FeCrCoSi alloy, make Fe1.5Cr0.5CoSi a preferred candidate for spintronic device applications.

The effect of MoS2 modified with Transition Metal (Fe, Co, Ni, Cu) on H2O adsorption: A first principle study

MoS2 has great potential as a humidity sensor, and doping is considered the most promising method to enhance the adsorption of H2O molecule by MoS2. Unfortunately, vacancy doping sacrifices the stability of the material while enhancing adsorption efficiency. Here, we use Fe, Co, Ni, Cu to modify the surface of MoS2 and study the adsorption characteristics of H2O molecule on MoS2 before and after modification. The first principles calculations further indicate that partial transition metal (TM) doping can induce spin polarization in MoS2. Spin polarization further enhances orbital hybridization between atoms, thereby improving adsorption performance. On the basis of qualitative analysis of thermodynamic stability and electrical properties, quantitative analysis was conducted on adsorption energy and charge transfer. The results indicate that the adsorption energy, in descending order, is Fe-MoS2 > Co-MoS2 > Ni-MoS2 > Cu-MoS2 > MoS2. Compared with MoS2, Fe-MoS2 has the best adsorption effect among the four doping systems, with an adsorption energy increase of 22.1 times. Importantly, simulations of desorption time have demonstrated that Fe-MoS2 and Co-MoS2 exhibit a significant reduction in desorption time with increasing temperature and can be rapidly recycled.

Manipulating dwell time and spin polarization via δ-doping for electrons in spin-orbit-coupling modulated magnetic nanostructure

With the help of atomic-layer doping technology, we theoretically explore how to use a δ-potential to manipulate a temporal electron-spin splitter (TESS), which is based on a spin-orbit-coupling (SOC) modulated magnetic nanostructure. Due to the SOC, the dwell time still depends on electron spins even if a δ-doping is embedded inside the TESS. Moreover, both the magnitude and sign of spin polarization ratio can be controlled by tuning the weight or position of the δ-doping. Therefore, a structurally manipulable TESS device can be obtained for semiconductor spintronic device applications.

Dynamic Nuclear Polarization with Conductive Polymers

AbstractThe low sensitivity of liquid‐state nuclear magnetic resonance (NMR) can be overcome by hyperpolarizing nuclear spins by dissolution dynamic nuclear polarization (dDNP). It consists of transferring the near‐unity polarization of unpaired electron spins of stable radicals to the nuclear spins of interest at liquid helium temperatures, below 2 K, before melting the sample in view of hyperpolarized liquid‐state magnetic resonance experiments. Reaching such a temperature is challenging and requires complex instrumentation, which impedes the deployment of dDNP. Here, we propose organic conductive polymers such as polyaniline (PANI) as a new class of polarizing matrices and report 1H polarizations of up to 5 %. We also show that 13C spins of a host solution impregnated in porous conductive polymers can be hyperpolarized by relayed DNP. Such conductive polymers can be synthesized as chiral and display current induced spin selectivity leading to electron spin hyperpolarization close to unity without the need for low temperatures nor high magnetic fields. Our results show the feasibility of solid‐state DNP in conductive polymers that are known to exhibit chirality‐induced spin selectivity.