Spin Polarization Effects Research Articles

Spin-polarization effects in the one-photon pair production in a supercritical magnetic field

A theoretical study is performed for the single-photon creation of an electron–positron pair in an external magnetic field. We present general expressions for process rates that are valid for arbitrarily high field strengths. Simple analytical expressions are obtained in the limiting cases of weak and strong fields. The emphasis is placed on the investigation of the spin alignment of the created particles as a function of the incident photon polarization and magnetic field strength. The obtained results show that the maximum value of the polarization degree of electrons (positrons) decreases in supercritical magnetic field.

Tailoring atomic chemistry to refine reaction pathway for the most enhancement by magnetization in water oxidation

Water oxidation on magnetic catalysts has generated significant interest due to the spin-polarization effect. Recent studies have revealed that the disappearance of magnetic domain wall upon magnetization is responsible for the observed oxygen evolution reaction (OER) enhancement. However, an atomic picture of the reaction pathway remains unclear, i.e., which reaction pathway benefits most from spin-polarization, the adsorbent evolution mechanism, the intermolecular mechanism (I2M), the lattice oxygen-mediated one, or more? Here, using three model catalysts with distinguished atomic chemistries of active sites, we are able to reveal the atomic-level mechanism. We found that spin-polarized OER mainly occurs at interconnected active sites, which favors direct coupling of neighboring ligand oxygens (I2M). Furthermore, our study reveals the crucial role of lattice oxygen participation in spin-polarized OER, significantly facilitating the coupling kinetics of neighboring oxygen radicals at active sites.

Spin polarization regulates photocatalytic CO2 into hydrocarbons by Co doped BiOCl

Doping magnetic elements into semiconductors is an effective strategy for manipulating spin-polarized electrons in photocatalysis. This work indicates that the introduction of spin-polarized electrons into BiOCl ultrathin sheets remarkably boosts the efficiency of photocatalytic CO2 reduction by doping BiOCl with magnetic Co. The Co-doped BiOCl (Co-BiOCl) photocatalyst selectively converts CO2 into CH4 and C2+ products with a hydrocarbon selectivity of 76.9 %, which is not available for pristine BiOCl. The spin-polarized electrons generated from Co-BiOCl promote CO adsorption, stabilize the key CO* intermediate, and significantly reduce the kinetic barrier to CH2* formation, tuning the subsequent hydrogenation and C−C coupling into hydrocarbons. The regulatory effect of spin polarization on photocatalytic CO2 reduction can also be observed for Fe-, Ni- or non-magnetic element Cu- doped BiOCl. Hence, this work provides new insight into the regulation of the photoreduction of CO2 to hydrocarbon products by spin-polarized electrons.

Investigation of ordered dispersive effect, charge density, thermal properties and disappearance of spin polarization in perovskite CsBeO3 under the influence of pressure-A DFT perspective

Full Potential Linearized Augmented Plane Wave method (FP-LAPW) was employed to investigate the behavior of cubic perovskite CsBeO3 under the influence of pressure. The spin polarized study has been carried out in PBE-GGA approximation under the application of pressure. The variation of pressure is attained by the appropriate reduction of volume for the compound. At equilibrium volume and at 0 GPa, the compound CsBeO3 is found to exhibit energy gap in the spin up direction and the spin down direction is largely conducting. With the reduction of volume and their corresponding increase in pressure, the electronic behavior changes for the compound. At a pressure of about 10 GPa, the s-orbital of Cs atom undergoes energy excitation to higher energy level due to an ordered dispersive effect at s-orbital. This results in the disappearance of energy gap and the compound becomes conducting in spin up direction and the half metallic ferromagnetism is found to disappear at increased pressure. Thermal properties such as Debye temperature and Curie point have been reported in this work. Elastic constants and anisotropy factor have been determined and compared at different pressures.

Magnetic Field‐Assisted Water Splitting: Mechanism, Optimization Strategies, and Future Perspectives

AbstractRationally designing of highly efficient electrocatalysts is critical to improving hydrogen production by water electrolysis. However, bottlenecks still require consideration when optimizing the intrinsic performance of electrocatalysts. Applying appropriate external fields to catalytic systems may effectively overcome such bottlenecks and enhance the performance of catalysts. Among various external fields, the magnetic field has received extensive attention owing to its multifunctionality, non‐contact nature, and non‐invasiveness, thereby requiring more research and development. In this review, recent advances in magnetic field‐assisted water electrolysis are systematically outlined. Firstly, the diverse methods used for pre‐regulating catalysts under magnetic fields, including optimized nucleation, induction heating, and directed growth, are discussed. It then explores the effects of magnetic fields on electrochemical processes, including magnetothermal, magnetohydrodynamic, and induced electric impact. Then, the influences of magnetic fields on the intrinsic properties of catalysts, such as spin polarization and spin reconstruction effects, are addressed. Finally, a discussion of the potential perspectives of magnetic field‐enhanced water splitting, including catalyst design, experimental precision, and in situ characterization, are then provided to guide further research.

Effects of spin polarization on the propagation of surface waves on a quantum plasma half-space

The study explores the wave propagation characteristics of surface plasma waves in a semi-bounded plasma, incorporating the influence of spin polarization arising from spin mismatch. The formulated plasma model integrates the density correlation effect via Bohm's potential force, Fermi pressure employing Fermi-Dirac statistics, and the exchange potential. These factors are considered in spin-polarized form and interconnected through the spin polarization index κ. We derive a dispersion relation for surface plasma waves, delineating the propagation features of the configured wave mode. Our findings indicate that an increase in spin polarization among electron populations results in a decrease in the phase velocity of surface plasma waves compared to the usual electron-ion quantum plasma. Moreover, an increase in the exchange potential contributes to a decrease in the phase speed. However, the ratio of plasmon to Fermi energy leads to an increase in the phase velocity of surface plasma waves in a spin-polarized quantum plasma. We provide a comparative analysis of our work with an earlier model based on the gold–air interface, revealing that our model facilitates the propagation of surface plasma waves with higher frequencies across the wave vector. This study highlights the significance of quantum effects for electrostatic surface plasma waves in dense metallic plasmas at room temperature, with implications for signal transmission in metallic waveguides observed in a recent study [Guo et al., “Excitation of graphene magneto-plasmons in terahertz range and giant Kerr rotation,” J. Appl. Phys. 125(1), 013102 (2019)] and some of the references therein.

Accurate prediction of the optical properties of nanoalloys with both plasmonic and magnetic elements

The alloying process plays a pivotal role in the development of advanced multifunctional plasmonic materials within the realm of modern nanotechnology. However, accurate in silico predictions are only available for metal clusters of just a few nanometers, while the support of modelling is required to navigate the broad landscape of components, structures and stoichiometry of plasmonic nanoalloys regardless of their size. Here we report on the accurate calculation and conceptual understanding of the optical properties of metastable alloys of both plasmonic (Au) and magnetic (Co) elements obtained through a tailored laser synthesis procedure. The model is based on the density functional theory calculation of the dielectric function with the Hubbard-corrected local density approximation, the correction for intrinsic size effects and use of classical electrodynamics. This approach is built to manage critical aspects in modelling of real samples, as spin polarization effects due to magnetic elements, short-range order variability, and size heterogeneity. The method provides accurate results also for other magnetic-plasmonic (Au-Fe) and typical plasmonic (Au-Ag) nanoalloys, thus being available for the investigation of several other nanomaterials waiting for assessment and exploitation in fundamental sectors such as quantum optics, magneto-optics, magneto-plasmonics, metamaterials, chiral catalysis and plasmon-enhanced catalysis.

Spin Polarization: A New Frontier in Efficient Photocatalysis for Environmental Purification and Energy Conversion.

As a promising strategy to improve photocatalytic efficiency, spin polarization has attracted enormous attention in recent years, which could be involved in various steps of photoreaction. The Pauli repulsion principle and the spin selection rule dictate that the behavior of two electrons in a spatial eigenstate is based on their spin states, and this fact opens up a new avenue for manipulating photocatalytic efficiency. In this review, recent advances in modulating the photocatalytic activity with spin polarization are systematically summarized. Fundamental insights into the influence of spin-polarization effects on photon absorption, carrier separation, and migration, and the behaviors of reaction-related substances from the photon uptake to reactant desorption are highlighted and discussed in detail, and various photocatalytic applications for environmental purification and energy conversion are presented. This review is expected to deliver a timely overview of the recent developments in spin-polarization-modulated photocatalysis for environmental purification and energy conversion in terms of their practical applications.

Lattice dynamics in chiral tellurium by linear and circularly polarized Raman spectroscopy: crystal orientation and handedness

Linearly and circularly polarized Raman spectroscopy allows to identify crystallographic faces, chiral axis orientation and crystal handedness of chiral tellurium, interesting toward the development of multifunctional devices.

The mechanism of the molecular CISS effect in chiral nano-junctions.

The chirality induced spin selectivity (CISS) effect has been up to now measured in a wide variety of systems but its exact mechanism is still under debate. Whether the spin polarization occurs at an interface layer or builds up in the helical molecule is yet not clear. Here we have investigated the current transmission through helical polyalanine molecules as a part of a tunnel junction realized with a scanning tunneling microscope. Depending on whether the molecules were chemisorbed directly on the magnetic Au/Co/Au substrate or at the STM Au-tip, the magnetizations of the Co layer had been oriented in the opposite direction in order to preserve the symmetry of the IV-curves. This is the first time that the CISS effect is demonstrated for a tunneling junction without a direct interface between the helical molecules and the magnetic substrate. Our results can be explained by a spin-polarized or spin-selective interface effect, induced and defined by the helicity and electric dipole orientation of the molecule at the interface. In this sense, the helical molecule does not act as a simple spin-filter or spin-polarizer and the CISS effect is not limited to spinterfaces.

High Catalytic Activity of Co-centered 2D Metal Organic Frameworks toward Bifunctional Oxygen Evolution and Reduction Reactions: Rationalized by Spin Polarization Effect.

CoX4 (X = NH, S, and O) motifs have demonstrated their high catalytic activity in the platforms of metal organic frameworks (MOFs), however, the underlying reason is still unrevealed. Herein, we propose monolayers constructed by linking TMNxO4-x motifs (TM = Fe, Co, Ni, Cu) with trioxotriangulenes (TOTs) as suitable models to clarify the structure-property-performance relationship of 2D MOFs for the oxygen evolution/reduction reaction (OER/ORR). The highly robust catalytic activity of CoNxO4-x for both the OER and the ORR has been confirmed, even surpassing that of most previously reported 2D MOFs and SACs. This activity is attributed to the moderate interaction between Co and the key intermediate species, which can be modulated by the coordinating atoms. We reveal spin momentum as a reliable activity descriptor in rationalizing the OER/ORR activity, which can be extended to many other 2D MOFs. The elucidated structure-activity relationship is significant for the development of effective bifunctional OER/ORR electrocatalysts.

Spin-Polarized Surface Capacitance Effects Enable Fe3 O4 Anode Superior Wide Operation-Temperature Sodium Storage.

Fe3 O4 is widely investigated as an anode for ambient sodium-ion batteries (SIBs), but its electrochemical properties in the wide operation-temperature range have rarely been studied. Herein, the Fe3 O4 nanoparticles, which are well encapsulated by carbon nanolayers, are uniformly dispersed on the graphene basal plane (named Fe3 O4 /C@G) to be used as the anode for SIBs. The existence of graphene can reduce the size of Fe3 O4 /C nanoparticles from 150 to 80nm and greatly boost charge transport capability of electrode, resulting in an obvious size decrease of superparamagnetic Fe nanoparticles generated from the conversion reaction from 5 to 2nm. Importantly, the ultra-small superparamagnetic Fe nanoparticles (≈2nm) can induce a strong spin-polarized surface capacitance effect at operating temperatures ranging from -40 to 60°C, thus achieving highly efficient Na-ion transport and storage in a wide operation-temperature range. Consequently, the Fe3 O4 /C@G anode shows high capacity, excellent fast-charging capability, and cycling stability ranging from -40 to 60°C in half/full cells. This work demonstrates the viability of Fe3 O4 as anode for wide operation-temperature SIBs and reveals that spin-polarized surface capacitance effects can promote Na-ion storage over a wide operation temperature range.

Role of Spin Polarization and Dynamic Correlation in Singlet-Triplet Gap Inversion of Heptazine Derivatives.

The new generation of proposed light-emitting molecules for organic light-emitting diodes (OLEDs) has raised considerable research interest due to its exceptional feature─a negative singlet-triplet (ST) gap violating Hund's multiplicity rule in the excited S1 and T1 states. We investigate the role of spin polarization in the mechanism of ST gap inversion. Spin polarization is associated with doubly excited determinants of certain types, whose presence in the wave function expansion favors the energy of the singlet state more than that of the triplet. Using a perturbation theory-based model for spin polarization, we propose a simple descriptor for prescreening of candidate molecules with negative ST gaps and prove its usefulness for heptazine-type molecules. Numerical results show that the quantitative effect of spin polarization decreases linearly with the increasing highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) exchange integral. Comparison of single- and multireference coupled-cluster predictions of ST gaps shows that the former methods provide good accuracy by correctly balancing the effects of doubly excited determinants and dynamic correlation. We also show that accurate ST gaps may be obtained using a complete active space model supplemented with dynamic correlation from multireference adiabatic connection theory.

Effect of Co doping of (Ga, In) and 2N preferred orientation on the magnetic and optical properties of ZnO

Current research on the Zn1−xMxO1−yNy (M = Ga, In) system mainly focuses on the p-type property, where Ga–N or In–N has different preferred orientations for bonding. Studies on the magnetic, bandgap, and optical properties of ZnO co doped with N are also lacking. The generalized gradient approximation (GGA+U) plane wave ultrasoft pseudopotential method based on density functional theory is used to systematically investigate the effects of the magnetic, band gap, and optical properties of the system for addressing the aforementioned problems. Results show that the formation energy of the Zn1−xMxO1−yNy (M = Ga, In) system is negative, all doping is easy, and all doped systems are stable and magnetic. The magnetism comes from the double exchange effect of electron spin polarization. Research has found that the band gap in Ga–N or In–N bonding along the c-axis direction is narrower than that along the a-axis direction. In the low-energy region, the redshift of the absorption spectrum is more significant, and the absorption or reflection coefficient and the carrier polarization and activity are stronger. In particular, In–N forms bonds along the c-axis direction and is co doped with another N in ZnO, which results in the narrowest band gap and the most significant redshift in the absorption spectrum. The absorption of sunlight can also be achieved in the ultraviolet visible near-infrared region. The absorption or reflection coefficient and the carrier polarization and activity are relatively strongest. This work has certain reference value for the design and preparation of new solar cell light absorbing materials based on ZnO.

Spin filtering in Dresselhaus spin-orbit-coupled, layered-semiconductor microstructure

Based on Dresselhaus spin-orbit-coupling effect in a layered semiconductor microstructure, an electron-spin filter is proposed. It is found that an obvious spin polarization effect appears and is related to electron energy and in-plane wave vector. It is also found that both magnitude and sign of spin polarization can be controlled by strain engineering or layer's thickness. This layered-semiconductor microstructure can act as a tunable spin filter.

Uncovering spin-orbit coupling-independent hidden spin polarization of energy bands in antiferromagnets

Many textbook physical effects in crystals are enabled by some specific symmetries. In contrast to such ‘apparent effects’, ‘hidden effect X’ refers to the general condition where the nominal global system symmetry would disallow the effect X, whereas the symmetry of local sectors within the crystal would enable effect X. Known examples include the hidden Rashba and/or hidden Dresselhaus spin polarization that require spin-orbit coupling, but unlike their apparent counterparts are demonstrated to exist in non-magnetic systems even in inversion-symmetric crystals. Here, we discuss hidden spin polarization effect in collinear antiferromagnets without the requirement for spin-orbit coupling (SOC). Symmetry analysis suggests that antiferromagnets hosting such effect can be classified into six types depending on the global vs local symmetry. We identify which of the possible collinear antiferromagnetic compounds will harbor such hidden polarization and validate these symmetry enabling predictions with first-principles density functional calculations for several representative compounds. This will boost the theoretical and experimental efforts in finding new spin-polarized materials.

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.

X-ray Spectroscopic Study of the Electronic Structure of a Trigonal High-Spin Fe(IV)═O Complex Modeling Non-Heme Enzyme Intermediates and Their Reactivity.

Fe K-edge X-ray absorption spectroscopy (XAS) has long been used for the study of high-valent iron intermediates in biological and artificial catalysts. 4p-mixing into the 3d orbitals complicates the pre-edge analysis but when correctly understood via 1s2p resonant inelastic X-ray scattering and Fe L-edge XAS, it enables deeper insight into the geometric structure and correlates with the electronic structure and reactivity. This study shows that in addition to the 4p-mixing into the 3dz2 orbital due to the short iron-oxo bond, the loss of inversion in the equatorial plane leads to 4p mixing into the 3dx2-y2,xy, providing structural insight and allowing the distinction of 6- vs 5-coordinate active sites as shown through application to the Fe(IV)═O intermediate of taurine dioxygenase. Combined with O K-edge XAS, this study gives an unprecedented experimental insight into the electronic structure of Fe(IV)═O active sites and their selectivity for reactivity enabled by the π-pathway involving the 3dxz/yz orbitals. Finally, the large effect of spin polarization is experimentally assigned in the pre-edge (i.e., the α/β splitting) and found to be better modeled by multiplet simulations rather than by commonly used time-dependent density functional theory.

Beyond Stereoisomeric Effects: Exploring the Importance of Intermolecular Electron Spin Interactions in Biorecognition.

This work shows that electron spin polarization and stereoisomeric effects make comparable contributions to the enantioselective binding of amino acids. Magneto-electrochemical quartz crystal microbalance methods are used to study the adsorption of chiral amino acids onto a monolayer film of chiral molecules that are spin polarized by an underlying ferromagnetic substrate. The direction of the electron spin polarization affects both the kinetics and thermodynamics of the enantiospecific adsorption of the amino acids. Comparison of these data with the circular dichroism (CD) spectra of the amino acid adsorbates shows that the CD spectrum of the interacting group provides a good figure-of-merit for predicting the contributions of electron spin to the intermolecular interaction. These findings demonstrate the importance of electron spin in enantioselective intermolecular interactions between chiral amino acids and represent a paradigm shift for how selectivity should be viewed in biorecognition.

Theoretical study of elastic electron scattering by zinc atoms in the framework of relativistic optical potential model

A theoretical study of integral and differential cross sections as well as of spin-polarization effects is reported for elastic electron scattering by zinc atoms at collision energies up to 3 keV. It has been shown that a P-wave shape resonance appears in the low-energy range of the integral cross sections. Its energy is about 0.19 and 0.20 eV, while its width is about 0.309 and 0.356 eV for the j = 3/2 and j = 1/2 total angular momentum of the electron, respectively. The differential cross sections of scattering and the Sherman-functions S(E,θ) are computed by the parameter-free complex optical potential method. The calculated data are in a good overall agreement with the available experimental and theoretical data in the literature. The energy and angular positions have been located for five critical minima in the differential cross sections. The low-energy minimum is located at [6.63 eV; 102.34°], while the high-energy minimum is at [347.53 eV; 124.11°]. Ten points for the scattered electrons' total spin-polarization (S=±1) have been found in the vicinity of the critical minima along with the energy and the angular widths of the spin-polarization peaks (where |S|≥0.9).