Spin Polarization Research Articles

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.

Field‐Free Spin‐Orbit Torque Switching in Perpendicularly Magnetized Ta/CoFeB/MgO/NiO/Ta with a Canted Antiferromagnetic Insulator NiO Interlayer

AbstractIn this study, deterministic current‐induced spin‐orbit torque (SOT) magnetization switching is achieved, particularly in systems with perpendicular magnetic anisotropy (PMA), without the need for a collinear in‐plane field, a traditionally challenging requirement. In a Ta/CoFeB/MgO/NiO/Ta structure, spin reflection at the MgO/NiO interface generates a spin current with an out‐of‐plane spin polarization component σz. Notably, the sample featuring 0.8 nm MgO and 2 nm NiO demonstrates an impressive optimal switching ratio approaching 100% without any in‐plane field. A systematic investigation of the effects of the MgO and NiO thickness demonstrates that the formation of noncollinear spin structures and canted magnetization in the ultrathin NiO interlayer plays a pivotal role to the field‐free SOT switching. The integration of NiO as an antiferromagnetic insulator effectively mitigates current shunting effects and enhances the thermal stability of the device. This advancement in the CoFeB/MgO system holds promise for significant applications in spintronics, marking a crucial step toward realizing innovative technologies.

Mechanism of Solid-State 1H Photochemically Induced Dynamic Nuclear Polarization in a Synthetic Donor-Chromophore-Acceptor at 0.3 T.

1H photochemically induced dynamic nuclear polarization (photo-CIDNP) has recently emerged as a tool to enhance bulk 1H nuclear magnetic resonance (NMR) signals in solids at magnetic fields ranging from 0.3 to 21.1 T, using synthetic donor-chromophore-acceptor (D-C-A) molecules as optically active polarizing agents (PAs). However, the mechanisms at play for the generation of spin polarization in these systems have not been determined but are essential for an in-depth understanding and further development of the process. Here, we introduce site-selective deuteration to identify the 1H photo-CIDNP mechanisms at 85 K and 0.3 T in D-C-A molecule PhotoPol. We find that the protons on the acceptor moiety are essential for the generation of polarization, establishing differential relaxation as the main mechanism. These results establish selective deuteration as a tool to identify and suppress polarization transfer mechanisms, which opens up pathways for further optimization of the optical PA at both low and high magnetic fields.

Accelerating T1 relaxation time measurements of noble gas using transverse low-frequency square-wave magnetic field modulation.

The longitudinal relaxation time (T1) of noble gas nuclear spins is a critical parameter for evaluating the performance of an atomic comagnetometer, significantly influencing the signal-to-noise ratio of the system. Traditional measurement techniques, such as the free induction decay method combined with the spin growth technique (FIDSG), are time-consuming for gases with extended T1 durations, such as 21Ne, and are prone to substantial environmental variability. Here, we propose the transverse low-frequency square-wave magnetic field modulation (LSMM) method for the rapid measurement of T1. The experiment indicates that the LSMM significantly condenses the measurement time to 19.2% of the original, thereby diminishing the robustness demands of the system. Although a minor discrepancy of up to 3 min (or 1.3%) exists between LSMM and FIDSG results, the LSMM method provides strong support for calibrating the performance of comagnetometer cells and conducting various nuclear spin polarization experiments, thereby improving efficiency and reducing energy loss.

Current-induced spin polarization and spin Hall effect in III-V compounds two-dimensional materials

Current-induced spin polarization and spin Hall effect in III-V compounds two-dimensional materials

Interface‐Triggered Spin‐Magnetic Effect in Rare Earth Intraparticle Heterostructured Nanoalloys for Boosting Hydrogen Evolution

AbstractRare earth (RE) elements are attractive for spin‐magnetic modulation due to their unique 4 f electron configuration and strong orbital couplings. Alloying RE with conventional 3d transition‐metal (TM) is promising for the fabrication of advanced spin catalysts yet remains much difficulties in preparation, which leads to the mysteries of spin‐magnetic effect between RE and 3d TM on catalysis. Here we define a solid‐phase synthetic protocol for creating RE‐3d TM‐noble metal integrated intraparticle heterostructured nanoalloys (IHAs) with distinct Gd and Co interface within the entire Rh framework, denoted as RhCo−RhGd IHAs. They exhibit interface‐triggered antiferromagnetic interaction, which can induce electron redistribution and regulate spin polarization. Theoretical calculations further reveal that active sites around the heterointerface with weakened spin polarization optimize the adsorption and dissociation of H2O, thus promoting alkaline hydrogen evolution catalysis. The RhCo−RhGd IHAs show a small overpotential of 11.3 mV at 10 mA cm−2, as well as remarkable long‐term stability, far superior to previously reported Rh‐based catalysts.

Interface-Triggered Spin-Magnetic Effect in Rare Earth Intraparticle Heterostructured Nanoalloys for Boosting Hydrogen Evolution.

Rare earth (RE) elements are attractive for spin-magnetic modulation due to their unique 4 f electron configuration and strong orbital couplings. Alloying RE with conventional 3d transition-metal (TM) is promising for the fabrication of advanced spin catalysts yet remains much difficulties in preparation, which leads to the mysteries of spin-magnetic effect between RE and 3d TM on catalysis. Here we define a solid-phase synthetic protocol for creating RE-3d TM-noble metal integrated intraparticle heterostructured nanoalloys (IHAs) with distinct Gd and Co interface within the entire Rh framework, denoted as RhCo-RhGd IHAs. They exhibit interface-triggered antiferromagnetic interaction, which can induce electron redistribution and regulate spin polarization. Theoretical calculations further reveal that active sites around the heterointerface with weakened spin polarization optimize the adsorption and dissociation of H2O, thus promoting alkaline hydrogen evolution catalysis. The RhCo-RhGd IHAs show a small overpotential of 11.3 mV at 10 mA cm-2, as well as remarkable long-term stability, far superior to previously reported Rh-based catalysts.

Differential and integral elastic cross sections for electrons and positrons collisions with carbon dioxide molecules

This study investigates the elastic scattering of electrons and positrons by carbon dioxide (CO2) molecules over a wide energy range from 1 eV to 1 KeV. We have computed differential and integral elastic cross-sections (DCS and ICS) using partial wave analysis and compared the theoretical results with available experimental data. Our findings show a strong correlation with experimental results, particularly at mid to high-energy ranges, validating the employed theoretical frameworks. Additionally, the Sherman function was examined to explore spin polarisation effects during scattering events. This research provides crucial insights for applications in atmospheric physics, materials science, and molecular scattering processes, demonstrating its direct relevance to real-world problems and paving the way for further investigation into particle-molecule interactions.

Effect of (Zr, Ta) doping on electronic and magnetic properties of zinc-blende MgTe DMS compound: AB-initio approach

This study utilizes density functional theory (DFT) and the Korringa-Kohn-Rostoker coherent potential approximation (KKR-CPA) to explore the effects of zirconium (Zr) and tantalum (Ta) doping on the electronic and magnetic properties of zinc-blende MgTe. The electronic configurations of Mg1-x(TM)xTe (TM = Zr, Ta) were analyzed, revealing that Zr induces magnetic behavior with near-total spin polarization, while Ta doping leads to metallic behavior with partial polarization. The variations in magnetic moments are largely determined by impurity concentrations, with ferromagnetic stability in both systems driven by a double exchange interaction mechanism. Additionally, Curie temperatures exceeding room temperature were observed for specific doping concentrations. These results suggest significant potential for MgTe-based materials in spintronic applications. The findings further illustrate that Zr-doped alloys display half-metallicity, making them especially promising for future spintronics device development. KEY WORDS: DMS, KKR-CPA, Polarization, Metallic behavior, Curie temperature, Double exchange, Spintronic Bull. Chem. Soc. Ethiop. 2025, 39(1), 153-164. DOI: https://dx.doi.org/10.4314/bcse.v39i1.13

Particle-Hole Asymmetric Ferromagnetism and Spin Textures in the Triangular Hubbard-Hofstadter Model

In a lattice model subject to a perpendicular magnetic field, when the lattice constant is comparable to the magnetic length, one enters the “Hofstadter regime,” where continuum Landau levels become fractal magnetic Bloch bands. Strong mixing between bands alters the nature of the resulting quantum phases compared to the continuum limit; lattice potential, magnetic field, and Coulomb interaction must be treated on equal footing. Using determinant quantum Monte Carlo and density matrix renormalization group techniques, we study this regime numerically in the context of the Hubbard-Hofstadter model on a triangular lattice. In the field-filling phase diagram, we find a broad wedge-shaped region of ferromagnetic ground states for filling factor ν≤1, bounded below by filling factor ν=1 and bounded above by half filling the lowest Hofstadter subband. We observe signatures of SU(2) quantum Hall ferromagnetism at filling factors ν=1 and ν=3. The phases near ν=1 are particle-hole asymmetric, and we observe a rapid decrease in ground-state spin polarization consistent with the formation of skyrmions only on the electron doped side. At large fields, above the ferromagnetic wedge, we observe a low-spin metallic region with spin correlations peaked at small momenta. We argue that the phenomenology of this region likely results from exchange interaction mixing fractal Hofstadter subbands. The phase diagram derived beyond the continuum limit points to a rich landscape to explore interaction effects in magnetic Bloch bands. Published by the American Physical Society 2024

Visible Light-Sensitive Sustainable Quantum Dot Crystals of Co/Mg Doped Natural Hydroxyapatite Possessing Antimicrobial Activity and Biocompatibility.

Cutting-edge research in advanced materials is increasingly turning toward the development of novel multifunctional nanomaterials for use in high-tech applications. This research uses the solid-state method as a solvent-free technique to create multifunctional quantum dot (QD) hydroxyapatite (HA) crystals from bovine bone waste. By incorporating cobalt (Co) and magnesium (Mg) into the HA structure, the crystallinity of the hexagonal HA nanoparticles (99.7%), showing QD crystals is enhanced. Oxygen vacancies on the surfaces of the HA nanoparticles contributed to their bandgap falling within the visible light range. In addition, the dopants substituted calcium in the HA crystal structure and generated a divalent oxidation state, shifting the bandgap of natural HA toward red wavelengths (3.26 to 1.94eV). Moreover, the incorporation of Co led to magnetization within the HA structure through spin polarization. Additionally, the doped QD crystals of HA nanoparticles showed significant antimicrobial activity against Escherichia coli, Staphylococcus aureus, and bacteriophages MS2, particularly under visible light exposure. In short, the Co/Mg co-doped HA nanoparticles exhibited ferromagnetic properties, sensitivity to visible light, biocompatibility, and considerable antimicrobial effects, establishing their potential as sustainable multifunctional materials for biomedical applications, especially in anti-infection treatments.

Femtotesla atomic magnetometer with counter-propagating optical sideband pumping.

The ultrasensitive magnetometer has a vital importance in fundamental research and applications. Currently, the spin-exchange relaxation-free (SERF) atomic magnetometer has been reported with a sensitivity around the level of fT/Hz1/2. To enhance the sensitivity, a gradiometer configuration has usually been introduced to cancel the common-mode noise between two separate channels. However, the signal and response from different channels are not the same due to the attenuation of the pump beam. Here, we proposed a counter-propagating optical sideband pumping method to polarize the atoms, using the electro-optic modulator to modulate the single-pump beam, generating two symmetrically red- and blue-detuned sidebands of frequency. This scheme leads to a significant reduction of undesirable effects coming along with the optical pumping, such as light shifts and spatial inhomogeneity in atomic spin polarization. With the help of this pumping scheme, the two channels have the same magnetic response, and we have built a gradiometer atomic magnetometer with a sensitivity of 0.5 fT/Hz1/2 ranging from 5 to 40 Hz. Our results propose the possibility of creating larger arrays of atomic magnetometers (AMs) with high sensitivity and spatial resolution based on single-vapor cells for magnetocardiography and magnetoencephalography imaging or searching for exotic spin-dependent interactions.

Exploration of lead free half-metallic double perovskites Li2Mo(Cl/Br)6 for spintronic device: DFT-calculations

The intrinsic spin of electrons has revolutionized the various aspects in the field of electronics, like data storage and quantum computing. Magnetic, structural, mechanical, transport and thermoelectric aspects of the Li2Mo(Cl/Br)6 double perovskites have been examined using the Wein2k and BoltzTraP code. These compounds having cubic structure with negative enthalpy of formation confirms their thermodynamic stability. The energy versus volume optimization for both ferromagnetic (FM) and antiferromagnetic phases (AFM) indicate AFM state due to greater release of energy in this configuration. Double exchange model p-d hybridization for partial density of states (PDOS) is investigated in band structures and half-metallicity feature is reported. The spin–orbit interaction with hybridization in d states of Mo and integral magnetic moment reveals strong spin polarization. The thermoelectric features (Seebeck coefficient, power factor, and figure of merit, electrical and thermal conductivities) have also been evaluated for utilization of these compounds in spintronics appliances.

Chirality Engineering of Nanostructured Copper Oxide for Enhancing Oxygen Evolution from Water Electrolysis.

The exploration of a new conceptual strategy for improving the oxygen evolution reaction (OER) of earth-abundant electrocatalysts is critical. In this study, chiral copper oxide nanoflower is explored by a self-assembly method. The characterization suggests the chiral structure originates from the crystal plane-level helical stack of the secondary nanosheets. Of note, the assembly illustrates a record-high degree of spin polarization of 96%, indicating the ideal alignment of electron spin. Moreover, density function theory calculations show the chiral structure reducing the reaction energy barrier (REB) while switching the potential-determining step from *O→*OOH to *OH→*O. Together with the enhanced electrochemical active surface area and accelerated charge transfer, the production of ground-state triplet O2 is improved via a spin-forbidden route that involves the singlet H2O/OH•. Consequently, the chiral nanoflower shows a overpotential of 308mV at 10mA cm-2 and a Tafel slope of 93.5mV dec-1, which is even superior to the commercial RuO2 (310mV, 101mV dec-1). This study presents a new strategy for improving the OER activity by simultaneously enhancing electronic properties and lowering the REB of an non-noble electrocatalyst via chirality engineering.

Creating Spin Channels in SrCoO3 through Triagonal-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 microscope, 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.

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

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

Hole and electron spin lifetime in lightly n-doped silicon at low temperatures

We report on photoinduced inverse spin-Hall effect (ISHE) measurements as a function of the incident photon energy in the 4–50 K temperature range for a Pt/n-doped Si junction. Optical spin injection allows generating a spin-oriented population of electrons and holes around the Δ valleys and Γ point of the Si Brillouin zone, respectively. Spin-polarized carriers cross the Pt/Si contact and then enter the Pt overlayer, where spin-to-charge conversion occurs by means of spin-dependent scattering with Pt nuclei. For temperatures T up to 20 K, most of the dopants are not ionized, so that the electric field, stemming from the contact potential between Pt and Si, extends to the whole Si substrate, which becomes insulating, and only spin-oriented holes reach the Pt layer and contribute to the ISHE spectra. For T>20 K, donors are partially ionized, and the resulting space charge close to the Pt/Si interface leads to the formation of a Schottky contact where the electric field rapidly vanishes within a few micrometers. As a consequence, also spin-polarized electrons enter Pt by means of thermionic emission, contributing to the ISHE signal. We numerically solve the one-dimensional spin drift-diffusion equations for holes and electrons and estimate the temperature dependence of the spin lifetime in Si for both populations, demonstrating that Si may serve as a versatile platform for spintronic applications, able to leverage both electrons and holes.

Circular photocurrents in centrosymmetric semiconductors with hidden spin polarization

Centrosymmetric materials with site inversion asymmetries possess hidden spin polarization, which remains challenging to be converted into spin currents because the global inversion symmetry is still conserved. This study demonstrates the spin-polarized circular photocurrents in centrosymmetric transition metal dichalcogenide semiconductors at normal incidence without applying electric bias. The global inversion symmetry is broken by using a spatially-varying circularly polarized light beam, which could generate spin gradient owing to the hidden spin polarization. The dependence of the circular photocurrents on electrode configuration, illumination position, and beam spot size indicates an emergence of circulating electric current under spatially inhomogeneous light, which is associated with the deflection of spin-polarized current through the inverse spin Hall effect. The circular photocurrents is subsequently utilized to probe the spin polarization and the inverse spin Hall effect under different excitation wavelengths and temperatures. The results of this study demonstrate the feasibility of using centrosymmetric materials with hidden spin polarization and non-vanishing Berry curvature for spintronic device applications.

Homogeneous Catalysts for Hydrogenative PHIP Used in Biomedical Applications

AbstractAt present, two competing hyperpolarization (HP) techniques, dissolution dynamic nuclear polarization (DNP) and parahydrogen (para‐H2) induced polarization (PHIP), can generate sufficiently high liquid state 13C signal enhancement for in vivo studies. PHIP utilizes the singlet spin state of para‐H2 to create non‐equilibrium spin populations. In hydrogenative PHIP, para‐H2 is irreversibly added to unsaturated precursors, typically in the presence of a homogeneous catalyst. The hydrogenation catalyst plays a crucial role in converting the singlet spin order of para‐H2 into detectable nuclear polarization. Currently, rhodium(I) bisphosphine complexes are the most widely employed catalysts for PHIP, capable of catalyzing the addition of para‐H2 to unsaturated precursors in organic solvents or aqueous media, depending on the ligand. Chiral catalysts enable the stereoselective production of hyperpolarized substrates. Ruthenium(II) piano stool complexes are capable of trans addition and are used to generate hyperpolarized fumarate. However, these catalysts systems are not optimal, and the greatest source of nuclear spin polarization loss is attributed to the mixing of singlet and triplet states of the protons derived from the para‐H2 during the hydrogenation process. Hence, future efforts should focus on enhancing the efficiency and kinetics of these catalysts.

Non-perturbative suppression of Chiral Effects in hot QGP for Λ/Λ̄-hyperons spin polarization in heavy-ion collisions

Non-perturbative suppression of Chiral Effects in hot QGP for Λ/Λ̄-hyperons spin polarization in heavy-ion collisions