Spin Polarization Research Articles

Spin Polarization via Adiabatic and Counterdiabatic Engineering

Spin Polarization via Adiabatic and Counterdiabatic Engineering

Engineering Metal Electron Spin Polarization to Regulate p‐Band Center of Se for Enhanced Sodium‐Ion Storage

Engineering Metal Electron Spin Polarization to Regulate p‐Band Center of Se for Enhanced Sodium‐Ion Storage

Exploring Geometric Chirality in Nanocrystals for Boosting Solar-to-Hydrogen Conversion.

Advancing catalyst design is pivotal for the enhancement of photocatalytic processes in renewable energy conversion. The incorporation of structural chirality into conventional inorganic solar hydrogen nanocatalysts promises a significant transformation in catalysis, a feature absent in this field. Here we unveil the unexplored potential of geometric chirality by creating a chiral composite that integrates geometric chiral Au nanoparticles (NPs) with two-dimensional C3N4 nanosheets, significantly boosting photocatalytic H2 evolution beyond the achiral counterparts. The superior performance is driven by the geometric chirality of Au NPs, which facilitates efficient charge carrier separation through the favorable C3N4-chiral Au NP interface and chiral induced spin polarization, and exploits high-activity facets within the concave surfaces of chiral Au NPs. The resulting synergistic effect leads to a remarkable increase in photocatalytic H2 evolution, with an apparent quantum yield of 44.64% at 400 nm. Furthermore, we explore the selective polarized photo-induced carrier separation behavior, revealing a distinct chiral-dependent photocatalytic HER performance. Our work advances the design and utilization of chiral inorganic nanostructures for superior performance in energy conversion processes.

Influence of Photoexcitation Conditions on the Spin Polarization of Nitrogen-Vacancy Centers in Isotopically Enriched Silicon Carbide 6H-28 SiC

Influence of Photoexcitation Conditions on the Spin Polarization of Nitrogen-Vacancy Centers in Isotopically Enriched Silicon Carbide 6H-28 SiC

Manipulating Ferroelectric Polarization and Spin Polarization of 2D CuInP2S6 Crystals for Photocatalytic CO2 Reduction.

Manipulating electronic polarizations such as ferroelectric or spin polarizations has recently emerged as an effective strategy for enhancing the efficiency of photocatalytic reactions. This study demonstrates the control of electronic polarizations modulated by ferroelectric and magnetic approaches within a two-dimensional (2D) layered crystal of copper indium thiophosphate (CuInP2S6) to boost the photocatalytic reduction of CO2. We investigate the substantial influence of ferroelectric polarization on the photocatalytic CO2 reduction efficiency, utilizing the ferroelectric-paraelectric phase transition and polarization alignment through electrical poling. Additionally, we explore enhancing the CO2 reduction efficiency by harnessing spin electrons through the synergistic introduction of sulfur vacancies and applying a magnetic field. Several advanced characterization techniques, including piezoresponse force microscopy, ultrafast pump-probe spectroscopy, in situ X-ray absorption spectroscopy, and in situ diffuse reflectance infrared Fourier transformed spectroscopy, are performed to unveil the underlying mechanism of the enhanced photocatalytic CO2 reduction. These findings pave the way for manipulating electronic polarizations regulated through ferroelectric or magnetic modulations in 2D layered materials to advance the efficiency of photocatalytic CO2 reduction.

Deterministic switching of perpendicular magnetization by out-of-plane anti-damping magnon torques.

Spin-wave excitations of magnetic moments (or magnons) can transport spin angular momentum in insulating magnetic materials. This property distinguishes magnonic devices from traditional electronics, where power consumption results from electrons' movement. Recently, magnon torques have been used to switch perpendicular magnetization in the presence of an external magnetic field. Here we present a material system composed of WTe2/antiferromagnetic insulator NiO/ferromagnet CoFeB heterostructures that allows magnetic field-free switching of the perpendicular magnetization. The magnon currents, with a spin polarization canting of -8.5° relative to the sample plane, traverse the 25-nm-thick polycrystalline NiO layer while preserving their original polarization direction, subsequently exerting an out-of-plane anti-damping magnon torque on the ferromagnetic layer. Using this mechanism, we achieve a 190-fold reduction in power consumption in PtTe2/WTe2/NiO/CoFeB heterostructures compared to Bi2Te3/NiO/CoFeB control samples, which only exhibit in-plane magnon torques. Our field-free demonstration contributes to the realization of all-electric, low-power, perpendicular magnetization switching devices.

Spin-Charge Conversion in Chiral Polymers with Hopping Conduction.

Organic and biological materials are often chiral. Chiral polymers, as recent experiments indicate, facilitate spin-charge conversion: a charge current results in a spin polarization and vice versa, dubbed chirality-induced spin selectivity (CISS) and inverse CISS (ICISS). While CISS/ICISS in crystalline chiral systems such as tellurium can be understood in terms of their chirality- and spin-dependent band structure, such a picture becomes inapplicable to disordered chiral polymers, where carrier transport is via hopping rather than band conduction. Here, we develop a microscopic theory to describe CISS and ICISS in disordered chiral organics, in which chirality-induced geometric spin-orbit coupling leads to a purely geometric spin-dependent Berry phase in electron hops involving triads, whose orientations are dictated by the material's chirality. Our theory reveals a central role of spin-flip hopping, which suppresses CISS but enables ICISS.

Spin Symmetry Breaking-Induced Hubbard Gap Near-Closure in N-Coordinated MnO2 for Enhanced Aqueous Zinc-Ion Battery Performance.

Transition metal oxides (TMOs) are promising cathode materials for aqueous zinc ion batteries (ZIBs), however, their performance is hindered by a substantial Hubbard gap, which limits electron transfer and battery cyclability. Addressing this, we introduce a heteroatom coordination approach, using triethanolamine to induce axial N coordination on Mn centers in MnO2, yielding N-coordinated MnO2 (TEAMO). This approach leverages the change of electronegativity disparity between Mn and ligands (O and N) to disrupt spin symmetry and augment spin polarization. This enhancement leads to the closure of the Hubbard gap, primarily driven by the intensified occupancy of the Mn eg orbitals. The resultant TEAMO exhibit a significant increase in storage capacity, reaching 351 mAh g-1 at 0.1 A g-1. Our findings suggest a viable strategy for optimizing the electronic structure of TMO cathodes, enhancing the potential of ZIBs in energy storage technology.

Spin Symmetry Breaking‐Induced Hubbard Gap Near‐Closure in N‐Coordinated MnO2 for Enhanced Aqueous Zinc‐Ion Battery Performance

AbstractTransition metal oxides (TMOs) are promising cathode materials for aqueous zinc ion batteries (ZIBs), however, their performance is hindered by a substantial Hubbard gap, which limits electron transfer and battery cyclability. Addressing this, we introduce a heteroatom coordination approach, using triethanolamine to induce axial N coordination on Mn centers in MnO2, yielding N‐coordinated MnO2 (TEAMO). This approach leverages the change of electronegativity disparity between Mn and ligands (O and N) to disrupt spin symmetry and augment spin polarization. This enhancement leads to the closure of the Hubbard gap, primarily driven by the intensified occupancy of the Mn eg orbitals. The resultant TEAMO exhibit a significant increase in storage capacity, reaching 351 mAh g−1 at 0.1 A g−1. Our findings suggest a viable strategy for optimizing the electronic structure of TMO cathodes, enhancing the potential of ZIBs in energy storage technology.

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.

Modulating photocatalytic activity of nitrogen doped TiO2 nanoparticles via magnetic field

The effect of the magnetic field on the photocatalytic activity of TiO2-based nanoparticles is analyzed using a magnetically-assisted photoreactor with permanent magnets to generate a controlled uniform magnetic field, B (≈ 82 mT). Nitrogen doped TiO2 nanoparticles (sizes around 10 nm) were synthesized through a solvothermal method employing Ti(IV) butoxide and HNO3 (x = 0, 0.5, 1, 1.5 and 2 mL) as precursors and their structural, optical and magnetic properties were analyzed. Specifically, nitrogen doping is confirmed through Hard X-ray Photoelectron Spectroscopy (HAXPES) in those samples synthesized with low HNO3 concentrations (x = 0.5, 1). The correlation between spin polarization (magnetic susceptibility) and visible photocatalytic activity (methyl orange as a model organic pollutant) is particularly analyzed. Surprisingly, opposite effects of the magnetic field on the photocatalytic performance are found in the visible range (above 400 nm) or under UV-Vis irradiation (decrease and increase in the photocatalytic activity, respectively, under magnetic field). The Langmuir-Hinshelwood model allows us to conclude that the strong decrease in adsorption under the magnetic field (around 42 % for x = 0.5) masks the increase in the kinetic constant (close to 58 % for x = 0.5) related mainly to the effect of Lorentz forces on the reduction of the electron-hole recombination.

Employing lattice compression spin polarization electric field for boosting degradation of mixed antibiotics in wastewater

Localized polarization electric field is a key factor affecting photocatalytic activity. In this study, the localized polarization electric field of lattice strain was introduced into the electronic structure of Bi2WO6 by using the high and low valence state doping method. The impurity energy level induced by lattice strain further affects the gap energy level. As an intermediate state for electron transfer, the gap level further promotes the dynamics of photo generated charges, reducing the band gap by 0.4 eV and improving the photoelectric performance by 60 %. Various tests and theoretical calculations have confirmed that the internal electric field of local polarization significantly improves the generation and transfer rate of photo-generated charges, thereby boosting catalytic activity. The removal ratios of ciprofloxacin (CIP) and tetracycline (TC) in the mixed wastewater reach 91.5 % and 97.1 % in 90 min, respectively. Cyclic tests have shown that the electronic structure control exhibits excellent stability with removal ratios of CIP and TC of 83.9 % and 85.7 %, respectively. Finally, the 8C of CIP and the 11C and 19O of TC are most susceptible to the attack of free radicals generated by lattice compression spin polarization electric fields based on the theoretical calculations of the Fukui function and the analysis of intermediates. This work provides new insights into the design of catalysts for efficient photo generated charge dynamics with lattice strain.

Spin-anomalous-Hall unidirectional magnetoresistance in light-metal/ferromagnetic-metal bilayers

Nonreciprocal magnetotransport is one of the central topics in spintronics because of its importance for electrically probing magnetic information. Among numerous electrical probes used to read magnetic orders, unidirectional magnetoresistance (UMR), characterized by sign changes upon reversal of either current or magnetization, is currently a matter of great interest and has been identified in various spin–orbit-coupled bilayer systems composed of an (anti)ferromagnetic layer and a nonmagnetic layer with strong spin Hall effect. A recent theoretical work predicts that a spin-anomalous-Hall (SAH) UMR in those metallic conducting bilayers can originate from the spin-anomalous-Hall effect of the ferromagnetic layer and the structural inversion asymmetry. However, this type of UMR has not been reported experimentally. Here, we give the experimental evidence of spin-anomalous-Hall UMR in the light-metal/ferromagnetic-metal Cu/Co bilayers, where the emergence of net nonequilibrium spin density is attributed to the interfacial spin leakage asymmetry due to the spin memory loss effect at the Cu/Co interface and multiple spin reflections. We also show a highly tunable UMR in the Cu/Co/CuOx trilayer by varying the Cu thickness, which is due to the competition between the orbital Rashba effect in Co/CuOx and the spin-anomalous-Hall effect in Cu/Co. Our work widens the material choice for UMR device applications and provides an alternative approach to detect in-plane magnetization without an external spin polarizer.

Even-integer quantum Hall effect in an oxide caused by a hidden Rashba effect.

In the presence of a high magnetic field, quantum Hall systems usually host both even- and odd-integer quantized states because of lifted band degeneracies. Selective control of these quantized states is challenging but essential to understand the exotic ground states and manipulate the spin textures. Here we demonstrate the quantum Hall effect in Bi2O2Se thin films. In magnetic fields as high as 50 T, we observe only even-integer quantum Hall states, but there is no sign of odd-integer states. However, when reducing the thickness of the epitaxial Bi2O2Se film to one unit cell, we observe both odd- and even-integer states in this Janus (asymmetric) film grown on SrTiO3. By means of a Rashba bilayer model based on the ab initio band structures of Bi2O2Se thin films, we can ascribe the only even-integer states in thicker films to the hidden Rasbha effect, where the local inversion-symmetry breaking in two sectors of the [Bi2O2]2+ layer yields opposite Rashba spin polarizations, which compensate with each other. In the one-unit-cell Bi2O2Se film grown on SrTiO3, the asymmetry introduced by the top surface and bottom interface induces a net polar field. The resulting global Rashba effect lifts the band degeneracies present in the symmetric case of thicker films.

Evolution of structure, magnetism, and electronic/thermal-transports of Ti(Cr)-substituted Fe2CrV all-d-metal Heusler ferromagnets

All-d-metal full-Heusler alloys possess superior mechanical properties and high spin polarization, which would play an important role in spintronic applications. Despite this, their electrical and thermal transport properties have not been comprehensively investigated till now. In this work, we present an analysis on the evolution of structural, magnetic and transport properties of Cr- and Ti-substituted Fe2CrV all-d-metal Heusler alloys by combining theoretical calculations and experiments. Both series of alloys crystallize in Hg2CuTi-type structure. With increasing Ti doping, the calculated total magnetic moments of Fe50Cr25V25-xTix decrease linearly. The experimental saturation magnetization is highly consistent with theoretical calculations and Slater-Pauling rule when x < 4, indicating the highly ordered atomic occupation. The magnetization and Curie temperature can be significantly tuned by altering spin polarizations and exchange interactions. The introduction of the foreign atom, Ti, results in a linear increase in residual resistivity, while electron-phonon scattering keeps relatively constant. The maximum values for electrical and thermal transport properties are observed in the stoichiometric Fe2CrV composition.

Exploring spin current and dielectric switching characteristics of doped-multiferroic in hexagonal phase for advance RAM technology: A theoretical study

The single-phase bismuth ferrite BiFeO3 (BFO) has garnered significant interest due to its spintronic-based switching properties observed at room temperature. The first-principles calculations were executed to examine the spin-polarized electronic, dielectric, and structural characteristics of co-doped BFO with lanthanum (La) at A-site and cobalt (Co), nickel (Ni) at B-site in its hexagonal phase (Bi1-αLaαFe1-βNiβO3 with α = β = 0.04) with generalized gradient approximation (GGA-PBE). The highest value (1.01 × 10−11 A) of total current observed in La Ni co-doped BFO, featuring a distinct spin current of the same magnitude, attributed to spin polarization at the Fermi level (100 %). Additionally, Co-doped BFO exhibits the highest observed spin current density (1.05 × 109A/m2) and charge current density (1.03 × 10−5A/m2). In case of dielectric switching properties, the Ni-doped BFO displays the lowest values of linear dielectric polarization (6.00 × 10−2 C/m2), polarization charge at its interface (1.27 × 10−17 C), capacitance (4.23 × 10−15 F), and switching energy (3.81 × 10−19 J), which is particularly lower than the reported switching energy (1.92 aJ) of multiferroic capacitor.

Theoretical perspectives on the electronic, optical, mechanical, magnetic, and anisotropic behaviors of the quaternary Heusler alloys RhFeMnZ and IrMnCrZ (where Z = Si, Ge)

High-spin-polarised materials are the most promising candidates for spintronic devices. Here, the spin-polarised electronic structure, magnetism, mechanical, and optical properties of RhFeMnZ and IrMnCrZ (where Z = Si, Ge) Quaternary Heusler alloys were calculated by first-principles calculations. The calculations show that type III for the RhFeMnSi, RhFeMnGe, and IrMnCrSi and type I for the IrMnCrGe compound configuration is the most stable crystal structure for the studied alloys. The four alloys were found to have a half-metallic ferromagnetic structure with indirect band gaps in the majority spin channels of 0.957, 0.66, 0.745, and 0.891 eV for RhFeMnSi, RhFeMnGe, IrMnCrSi, and IrMnCrGe, respectively. They exhibit an appreciable total magnetic moment of 4 μB for RhFeMnZ (Z = Si, Ge) and 2 μB for IrMnCrZ (Z = Si, Ge). The results show that RhFeMnZ and IrMnCrZ (where Z = Si, Ge) are ferromagnetic half-metals with 100 % spin polarisation. The results of the elastic constants demonstrate the mechanical stability of RhFeMnZ and IrMnCrZ (where Z = Si, Ge) alloys. Optical properties such as dielectric function, absorption, reflectance, optical conductivity, and other optical properties were also probed. In the ultraviolet region, RhFeMnZ and IrMnCrZ (where Z = Si, Ge) are effective absorbers and have a high refractive index. Alloys are promising candidates for potential applications in spintronic devices.

Ultrafast spin transfer and its impact on the electronic structure.

Optically induced intersite spin transfer (OISTR) promises manipulation of spin systems within the ultimate time limit of laser excitation. Following its prediction, signatures of ultrafast spin transfer between oppositely aligned spin sublattices have been observed in magnetic alloys and multilayers. However, it is known neither from theory nor from experiment whether the band structure immediately follows the ultrafast change in spin polarization or whether the exchange split bands remain rigid. We show that ultrafast spin transfer occurs even in ferromagnetic gadolinium metal. Charge transfer between localized surface and extended valence-band states leads to a decrease of the surface spin polarization. This synchronously alters the exchange splitting of the bulk valence bands during laser excitation. Moreover, the onset of demagnetization can be tuned by over 200 fs by changing the temperature-dependent spin mixing. Our results show a promising route to ultrafast control of the magnetization, widening the impact and applicability of OISTR.

Regulating Spin Polarization via Axial Nitrogen Traction at Fe-N5Sites Enhanced Electrocatalytic CO2Reduction for Zn-CO2 Batteries.

Single Fe sites have been explored as promising catalysts for the CO2reduction reaction to value-added CO. Herein, we introduce a novel molten salt synthesis strategy for developing axial nitrogen-coordinated Fe-N5sites on ultrathin defect-rich carbon nanosheets, aiming to modulate the reaction pathway precisely. This distinctive architecture weakens the spin polarization at the Fe sites, promoting a dynamic equilibrium of activated intermediates and facilitating the balance between *COOH formation and *CO desorption at the active Fe site. Notably, the synthesized FeN5, supported on defect-richin nitrogen-doped carbon(FeN5@DNC), exhibits superior performance in CO2RR, achieving a Faraday efficiency of 99% for CO production (-0.4 V vs. RHE) in an H-cell, and maintaining a Faraday efficiency of 98% at a current density of 270 mA cm-2(-1.0 V vs. RHE) in the flow cell. Furthermore, the FeN5@DNC catalyst is assembled as a reversible Zn-CO2battery with a cycle durability of 24 hours. In-situ IR spectroscopy and density functional theory (DFT) calculations reveal that the axial N coordination traction induces a transformation in the crystal field and local symmetry, therefore weakening the spin polarization of the central Fe atom and lowering the energy barrier for *CO desorption.

Charge Transfer and Intersystem Crossing in Compact Naphthalenediimide-Phenothiazine Triads: Synthesis and Study of the Photophysical Property with Transient Optical and Electron Paramagnetic Resonance Spectroscopic Methods.

In order to obtain a long-lived charge separation (CS) state in compact electron donor-acceptor molecular systems, we prepared a series of naphthalenediimide (NDI)-phenothiazine (PTZ) triads, with phenylene as the linker between the donor and acceptor. Conformation restriction is imposed to control the mutual orientation of the NDI and PTZ units by attaching methyl groups on the phenylene linker to tune the electronic coupling between the donor and the acceptor. Moreover, the PTZ moiety was oxidized to sulfoxide to tune the ordering of the CS state and the 3LE state (LE: locally excited state). UV-vis absorption spectra indicate electronic coupling between NDI with the phenylene linker as well as the PTZ units, manifested by the appearance of a charge-transfer (CT) absorption band, whereas this coupling is devoid in the triads with conformation restriction imposed. Fluorescence is strongly quenched in the triads compared to the reference compound, indicating electron transfer upon photoexcitation. Femtosecond transient absorption spectra indicate that the CS takes 0.8 ps, and then the 3LE state is formed by charge recombination in 83 ps. Nanosecond transient absorption (ns-TA) spectra show that the 3NDI state was observed in nonpolar solvents such as cyclohexane (triplet state lifetime: 95.7 μs), whereas the CS state was observed in more polar solvents. The CS state lifetimes are up to 1.2 μs (in toluene). Time-resolved electron paramagnetic resonance spectra of the triads in toluene consist of two types of signals: CS states (narrower signals, ∼10 mT) and 3LE states (broader signals, ∼50 to 200 mT). In the spectra of the triads containing PTZ, the CS state signals dominate, whereas for the triads containing oxidized PTZ, the 3NDI signals (zero-field splitting D ≈ 2000 MHz) prevail, both observations being in agreement with the ns-TA spectral studies. The electron spin polarization phase pattern of the 3NDI states of the triads indicates that the intersystem crossing (ISC) mechanism is spin-orbit charge-transfer ISC. Considering the 3CS state as ion pairs, the electron-exchange energy (J) is determined to be -39 to -59 MHz, and the electron spin dipolar interaction is 83-92 MHz.