Spin Polarization Research Articles

Switching on and off the spin polarization of the conduction band in antiferromagnetic bilayer transistors.

Antiferromagnetic conductors with suitably broken spatial symmetries host spin-polarized bands, which lead to transport phenomena commonly observed in metallic ferromagnets. In bulk materials, it is the given crystalline structure that determines whether symmetries are broken and spin-polarized bands are present. Here we show that, in the two-dimensional limit, an electric field can control the relevant symmetries. To this end, we fabricate a double-gate transistor based on bilayers of van der Waals antiferromagnetic semiconductor CrPS4 and show how a perpendicular electric displacement field can switch the spin polarization of the conduction band on and off. Because conduction band states with opposite spin polarizations are hosted in the different layers and are spatially separated, these devices also give control over the magnetization of the electrons that are accumulated electrostatically. Our experiments show that double-gated CrPS4 transistors provide a viable platform to create gate-induced conductors with near unity spin polarization at the Fermi level, as well as devices with a full electrostatic control of the total magnetization of the system.

Scattering makes a difference in circular dichroic angle-resolved photoemission

Recent years have witnessed a steady progress towards blending two-dimensional quantum materials into technology, with future applications often rooted in the electronic structure. Since crossings and inversions of electronic bands with different orbital characters determine intrinsic quantum transport properties, knowledge of the orbital character is essential. Here, we benchmark angle-resolved photoelectron emission spectroscopy (ARPES) as a tool to experimentally derive orbital characters. For this purpose we study the valence electronic structure of two technologically relevant quantum materials, graphene and WSe2, and focus on circular dichroism that is believed to provide sensitivity to the orbital angular momentum. We analyze the contributions related to angular atomic photoionization profiles, interatomic interference, and multiple scattering. Regimes in which initial-state properties could be disentangled from the ARPES maps are critically discussed and the potential of using circular dichroic ARPES as a tool to investigate the spin polarization of initial bands is explored. For the purpose of generalization, results from two additional materials, GdMn6Sn6 and PtTe2, are presented in addition. This research demonstrates rich complexity of the underlying physics of circular dichroic ARPES, providing insights that will shape the interpretation of both past and future circular-dichroic ARPES studies. Published by the American Physical Society 2025

Robust half-metallic properties in two-dimensional CuCr₂Se₂X₂ (X = Cl, Br, I)

Abstract In recent years, the rapid development of two-dimensional magnetic materials has revolutionized the field of spintronics, driven by their unique ability to combine magnetism and electronic functionality at the atomic scale. Here, we investigate the monolayer CuCr2Se2X2 (X = Cl, Br, I), which exhibit robust ferromagnetic (FM) behavior and half-metallicity with 100% spin polarization. The strong FM coupling, mediated by superexchange interactions, is rooted in the unique electronic structure of the Cr d-orbitals. Our findings reveal high Curie temperatures (TC) exceeding room temperature, with the Br variant achieving a remarkable 586 K. These exceptional properties, including the ability to modulate exchange interactions through strain engineering, highlight CuCr2Se2X2 as a versatile platform for flexible, high-performance spintronic devices, paving the way for advancements in next-generation electronic applications.

All-microwave spectroscopy and polarization of individual nuclear spins in a solid.

Pushing the sensitivity of nuclear magnetic resonance spectroscopy to the single spin level would have a major impact in chemistry and biology and is the goal of intense research efforts. We report magnetic resonance spectroscopy measurements of individual nuclear spins in a crystal coupled to a neighboring paramagnetic center, detected using microwave fluorescence at millikelvin temperatures. We observe real-time quantum jumps of the nuclear spin state, a proof of their individual nature. By driving the forbidden transitions of the coupled electron-nuclear spin system, we also achieve single-spin solid-effect dynamical nuclear polarization. Relying exclusively on microwave driving and microwave photon counting, the methods reported here are, in principle, applicable to a large number of electron-nuclear spin systems, in a wide variety of samples.

Ultrafast Exciton and Spin Dynamics of Monolayer MoSi2N4 Studied by Non-Degenerate Pump-Probe Transient Transmission Spectroscopy.

2D materials have attracted numerous attention for their potential applications in nano-photoelectronic and valleytronic devices. Recently, a new 2D material, MoSi2N4 monolayer, is synthesized and reported, and predicted to have many unique properties. Here, its ultrafast photoelectron and spin dynamics using femtosecond-resolved transient differential transmission and Faraday rotation spectroscopies are investigated. Complex and diverse ultrafast dynamics of excitons are observed with increasing probe wavelength from 510 to 640nm, including fully positive and negative monotonic decaying dynamics as well as an initial positive (negative) peak followed by slow negative (positive) recovery dynamics, and are explained well based on the band structure of MoSi2N4 monolayer containing a deep defect level locating above the midpoint of direct bandgap at K valley. Spin polarization of A and B excitons is found controlled by the circular helicity of exciting light. The spin relaxation lifetime of B excitons is determined as ≈0.73ps.

Advancing Spin Controlled Electrocatalysis Using Chiral Gold Nanoparticles Functionalized Bimetallic Spinel Oxide

AbstractOxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are the foundations of renewable energy technology. However, both processes have significant activation barriers, severely limiting the overall performance of energy conversion devices that utilize ORR/OER. Though traditional catalyst design prioritizes crystal and electronic structure, understanding the detailed mechanism requires consideration of spin selection rules as the ground electronic state of diatomic oxygen is a triplet. Here, we demonstrate the enhancement of the electrocatalytic performance of Mn and Co‐based bimetallic spinel oxides by functionalizing with chiral gold nanoparticles. Chiral gold nanoparticles impart spin selective charge transfer during oxygen reduction, resulting in higher current density in comparison with the achiral composite catalyst. Furthermore, the onset potential gets reduced by 120 mV at 2.5 mA cm−2 current density toward the OER activity of the chiral gold nanoparticle functionalized catalyst, attributed to the spin polarization mechanisms via chiral induced spin selectivity effect. This work emphasizes the use of chirality in the transition metal‐based oxide to induce the spin polarization in the oxide‐based catalysts in advancing ORR and OER efficiencies that are very essential for the application in renewable energy technology.

Designing 2D h-BN/MnO2 heterostructure for enhanced spintronic MTJs:half-metallicity induction and high tunnel magnetoresistance performance

Abstract The realization of half-metallicity in two-dimensional (2D) materials has been extensively investigated in order to advance the development of next-generation nanospintronic devices. In this work, a theoretical study of the h-BN/MnO2 vertical vdW heterostructure has been investigated to manipulate electronic structure of ferromagnetic semiconductor MnO2. Our research reveals that due to the large potential difference at the heterojunction interface, the energy bands of the two materials are shifted, which results in the half-metallicity in monolayer MnO2. Furthermore, we designed an in-plane magnetic tunnel junction (MTJ) by using h-BN/MnO2 heterostructure as the electrodes and monolayer MnO2 as the barrier, and simulated its transport properties from density functional theory combined with nonequilibrium Green’s function. According to our calculations, the MTJ demonstrates perfect 100% spin polarization in PC owing to the single-channel conduction capability of half-metal MnO2. Also, we have considered the effect of the barrier width on tunnel magnetoresistance (TMR) of the MTJ. It is found that the TMR ratio can be adjusted by modifying the barrier width, with the maximum achievable value exceeding 108. Moreover, the MTJ exhibits a 100% spin filtering effect (SFE) in PC within the bias voltages of -0.1 ~ 0.1 V. Our results provide valuable guidance for experimental investigations into MTJs utilizing 2D magnetic vdW materials.

Versatile device structures in MoS2: Magneticswitching of perfect spin and valley polarizationstates as well as tunneling magnetoresistance

Abstract Valley polarization has been achieved in transition metal dichalcogenides (TMDs), particularly
molybdenum disulfide (MoS2), using polarized light. Two valley polarized states have also been
reported in ferromagnetic MoS2 junctions with circularly polarized light. The polarized states are
accessible by switching the polarization direction. Despite these advances in valley polarization, more
amenable options for electronic devices, such as electrostatic and/or magnetic gating, are desirable.
Here, we explore the possibility of having two well-defined valley polarization states in ferromagnetic
MoS2 junctions accessible by switching the magnetization direction. In addition, spin polarization
and tunneling magnetoresistance (TMR), opening the door for versatile devices in TMDs. In the
case of Ferromagnetic/Ferromagnetic Insulator/Normal Metal (FM/FI/NM) junctions, we find spin
valley polarization and negative TMR. However, two well-defined valley polarization states accessible
by reversing the magnetization direction are not possible. As an alternative, we study FM/NM/FI
MoS2 junctions, finding two well-defined polarization states for both the spin and valley degrees of
freedom. The states are accessible by changing the magnetization direction in the FI region. Here,
it is fundamental to apply electrostatic gating in the NM region to ensure the participation of holes
in the electronic transport or n-p-n transport. FM/NM/FI MoS2 junctions also show high positive
TMR values at the edges of the valence and conduction band.

Photoemission spectroscopy and ab-initio simulation of CrFeVGa and CoFeVSb: a comparative study

We present a comprehensive photoemission study of two Vanadium-based quaternary Heusler alloys, CrFeVGa and CoFeVSb, which are highly promising candidates for spintronics and topological quantum applications. CrFeVGa exhibits large anomalous Hall conductivity due to the large Berry curvature originating from its non-trivial topological bands. In contrast, CoFeVSb displays a spin-valve-like behavior alongside excellent thermoelectric properties, such as ultra-low thermal conductivity and high power factor at room temperature. By utilizing synchrotron x-ray photoemission spectroscopy and resonant photoemission spectroscopy, we have investigated the core levels and valence band of both the alloys. Our analysis shows that the V 3dstates are primarily responsible for the electronic states at the Fermi level which result in the high spin polarization, consistent with our theoretical predictions. The presence of the Fermi edge in the valence band spectra in both the systems confirms the predicted metallic or half/semi-metallic features. The observed spectra match qualitatively with our simulated partial density of states. A close inspection of the temperature dependent valence band spectra indicates that some of the intriguing bulk properties reported earlier on these two systems are intimately connected with their unique band structure topology. This in turn facilitate a deeper insight into the origin of such interesting properties of these alloys. Such direct measurements of electronic structure provide a guiding platform towards a better understanding of the anomalous properties of any material in general.

Iron doped MSe2 Monolayers (M=Mo, W): A First-Principles Study of Structural, Electronic, and Magnetic Properties

In this study, we examined the effects of iron doping on the electronic and magnetic properties of transition metal dichalcogenide (TMD) monolayers, specifically MoSe2 and WSe2, utilizing density functional theory (DFT). Our results demonstrate that strategic doping significantly alters the material properties. Structural analysis reveals that doped systems largely retain the original structure of MSe2ML (Mo, W), despite exhibiting minor lattice distortions. Total energy calculations indicate that these structures remain stable. The doping of Fe induces significant spin polarization in both MoSe2ML and WSe2ML. The spin-down and spin-up channels exhibit distinct band gaps: 1.09 eV (D) and 0.24 eV (I) for MoSe2ML, and 1.0 eV (D) and 0.27 eV (D) for WSe2ML, respectively. Iron doping also induces magnetization in these TMDs. Additionally, the introduction of spin polarization shows that neighbouring atoms around the impurity exhibit slight magnetization due to the localized effects of the dopant. The net magnetic moment for both MoSe2ML and WSe2ML with iron impurities is approximately 2 µB. The computer simulations enable precise doping which leads to improved and tunable properties of TMDs. Future development in electronics, spintronics and quantum computing are facilitated by the potential expansion of doped TMDs.

A Magnetic Field-Assisted Lithium-Oxygen Batteries with Enhanced Reaction Kinetics by Spin-Polarization Strategy.

Lithium-oxygen (Li-O2) batteries have attracted significant attention due to their ultra-high theoretical energy density, but are obstructed by the sluggish reaction kinetics at the cathode and high overpotential. Our previous researches have proved that energy fields such as light, force and heat are effective strategies to improve the reaction kinetics of Li-O2 batteries. Herein, we proposed a novel magnetic field-assisted Li-O2 batteries via a spin polarization strategy. By doping magnetic Mn2+ ions with spin polarization characteristics into CsPbBr3 (Mn-CsPbBr3) perovskite, a magnetic field-responsive cathode was designed and prepared. The incorporation of Mn2+ ions drives charge redistribution and spin polarization of CsPbBr3, which remarkably improve the carrier separation efficiency and the oxygen species adsorption energy. Increased spin-polarization of the magnetic elements by Zeeman effect in an external magnetic field results in the enhanced oxygen reduction and evolution reaction. In the magnetic field, a low overpotential of 0.40 V was obtained for Li-O2 batteries with Mn-CsPbBr3 cathodes which demonstrate an ultralow overpotential of 0.12 V and an ultra-high energy efficiency of 96.3% with the further illumination. The introduction of magnetic fields into the Li-O2 battery system and provides a new avenue for improving the reaction kinetics of rechargeable Li-O2 battery.

Spin Hall effect in 3d ferromagnetic metals for field-free switching of perpendicular magnetization: A first-principles investigation

Ferromagnetic metals, with the potential to generate spin current with unconventional spin polarization via the spin Hall effect, offer promising opportunities for field-free switching of perpendicular magnetization and for spin–orbit torque devices. In this study, we investigate two distinct spin Hall mechanisms in 3d ferromagnetic metals including spin–orbit coupling driven spin Hall effect in Fe, Co, Ni, and their alloys, and non-relativistic spin Hall effect arising from anisotropic spin-polarized transport by taking L10-MnAl as an example. By employing first-principles calculations, we examine the temperature and alloy composition dependence of spin Hall conductivity in Fe, Co, Ni, and their alloys. Our results reveal that the spin Hall conductivities with out-of-plane spin polarization in 3d ferromagnetic metals are on the order of 1000 ℏ/2e(Ω cm)−1 at 300 K, but with a relatively low spin Hall angles around 0.01–0.02 due to the large longitudinal conductivity. For L10-MnAl(101), the non-relativistic spin Hall conductivity can reach up to 10 000 ℏ/2e(Ω cm)−1, with a giant spin Hall angle around 0.25 at room temperature. By analyzing the magnetization switching process, we demonstrate deterministic switching of perpendicular magnetization without an external magnetic field by using 3d ferromagnetic metals as spin current sources. Our work may provide an unambiguous understanding of the spin Hall effect in ferromagnetic metals and pave the way for their potential applications in related spintronic devices.

Electronic, magnetic, and structural properties of V2CoAl: Experimental and computational study

Here, we present results of combined experimental and computations study of V2CoAl, a Heusler alloy that exhibits nearly perfect spin-polarization. Our calculations indicate that this material maintains a high degree of spin-polarization (over 90%) in the wide range of lattice parameters, except at the largest considered unit cell volume. The magnetic alignment of V2CoAl is ferrimagnetic, due to the antialignment of the magnetic moments of vanadium atoms in their two sublattices. The calculated total magnetic moment per formula unit is nearly integer at the optimal lattice parameter and at the smaller volumes of the unit cell, but it deviated from the integer values as the unit cell expands. This is consistent with the calculated variation in the degree of spin polarization with lattice constant. The expected ferrimagnetic behavior has been observed in the arc-melted V2CoAl sample, with a Curie temperature of about 80 K. However, the saturation magnetization is significantly smaller than the theoretical prediction of ∼2 μB/f.u., most likely due to the observed B2-type atomic disorder. The samples exhibit metallic electron transport across the measurement range of 2 K to 300 K.

Exploring swift heavy ion-induced perpendicular magnetic anisotropy and tunnel magnetoresistance in CoFe2O4/MgO/ZnFe2O4 multilayers: X-ray magnetic circular dichroism study

Magnetic tunnel junctions (MTJs), consisting of two ferromagnetic electrodes separated by an insulating layer, have been foundational in spintronics. This study expands the traditional MTJ framework by incorporating an antiferromagnetic electrode alongside a ferromagnetic one to elucidate the interplay between perpendicular magnetic anisotropy (PMA) and tunnel magnetoresistance (TMR). Specifically, we investigate the relationship among spin-orbital magnetic moments, PMA, and TMR in pristine and Ag-irradiated (200 MeV) thin films of CoFe2O4 (40 nm)/MgO (20 nm)/ZnFe2O4 (40 nm). Angle-dependent soft X-ray magnetic circular dichroism (XMCD), together with element-specific hysteresis loops at the Fe L-edge, reveals that both the pristine and swift heavy ion (SHI)-multilayer stacks display magnetic anisotropy, characterized by a decreased XMCD intensity from out-of-plane (perpendicular) to in-plane (parallel) geometry. This reduction in the XMCD intensity correlates with spin polarization, establishing a direct relationship with the TMR of the MTJ. Furthermore, the analysis confirms that TMR decreases as the measurement angle decreases. Therefore, this investigation underscores the pivotal role of spin-orbital magnetic moments in influencing the PMA and TMR properties of CoFe2O4/MgO/ZnFe2O4 MTJs.

Chirality-induced spin selectivity and current-driven spin and orbital polarization in chiral crystals

Chirality-induced spin selectivity and current-driven spin and orbital polarization in chiral crystals

High spin polarization and half-metallic ferromagnetism in novel Half–Heusler FeCrX (X = S, Se and Te) alloys using first-principles calculations

High spin polarization and half-metallic ferromagnetism in novel Half–Heusler FeCrX (X = S, Se and Te) alloys using first-principles calculations

Spin polarization regulation of Fe–N4 by Fe3 atomic clusters for highly active oxygen reduction reaction

Spin polarization regulation of Fe–N4 by Fe3 atomic clusters for highly active oxygen reduction reaction

Can ΔSCF and ROKS DFT-Based Methods Predict the Inversion of the Singlet-Triplet Gap in Organic Molecules?

Inverted singlet-triplet gap systems (INVEST) have emerged as an intriguing class of materials with potential applications as emitters in Organic Light Emitting Diodes (OLEDs). Indeed, this type of material exhibits a negative singlet-triplet energy gap (ΔEST), i.e., an inversion of the lowest singlet (S1) and triplet (T1) excited states, that goes against Hund's rule. In this study, the ΔEST of a set of 15 INVEST molecules has been computed within the framework of Restricted Open-Shell Kohn-Sham (ROKS) and Delta Self-Consistent Field (ΔSCF) methods and the results were benchmarked against wavefunction-based calculations performed at the EOM-CCSD, NEVPT2, and SCS-CC2 levels. We find that ROKS always (and wrongly) predicts a positive ΔEST with global hybrid, meta-GGA, and long-range corrected functionals and that this is almost functional-independent. We also show that the only way to obtain an inverted gap was to resort to double hybrid functionals. In contrast, using the above-mentioned functionals, ΔSCF usually gives a negative ΔEST, although the results are largely functional-dependent. Overall, applying a ΔSCF method based on the PBE0 functional provides the lowest MSD and MAD with respect to the EOM-CCSD results. We further show that the singlet-triplet inversion is driven by different degrees of orbital relaxation in the singlet versus triplet state and that this is well captured by ΔSCF calculations. As a matter of fact, this orbital relaxation in ΔSCF somehow mimics the involvement of double and higher-order excitations in EOM-CCSD, which leads to a difference in spatial localization of the α and β spins, and thus introduces (local) spin polarization effects sourcing the negative ΔEST. However, care should be taken when using the ΔSCF method to screen materials with potential INVEST behavior in view of their limited quantitative correlation with reference EOM-CCSD results on the molecular data basis used here.

Driving force of atomic ordering in Fe-Pt alloys, investigated by density functional theory and machine-learning interatomic potentials Monte Carlo simulations.

We report the mechanisms of atomic ordering in Fe-Pt bimetallic alloys
using density functional theory (DFT) and machine-learning interatomic potential
Monte Carlo (MLIP-MC) simulations. We clarified that the formation enthalpy of
the ordered phase was significantly enhanced by spin polarization compared to that
of the disordered phase. Analysis of the density of states indicated that coherence
in local potentials in the ordered phase brings energy gain over the disordered phase,
when spin is considered. MLIP-MC simulations were performed to investigate the
phase transition of atomic ordering at finite temperatures. The model trained using
the DFT dataset with spin polarization exhibited quantitatively good agreement with
previous experiments and thermodynamic calculations across a wide range of Pt
compositions. In contrast, the model without spin significantly underestimated the
transition temperature. Through this study, we clarified that spin polarization is
essential for accurately accounting for the ordered phase in Fe-Pt bimetallic alloys,
even above the Curie temperature, possibly because of the remaining short-range spin
order.

Highly Conductive Chiral Organic Cages and Their Helical Assemblies Enable Efficient Spin Filtering.

Chiral molecular cages are demonstrated to have unique applications in enantioselective chemistry owing to their 3D cage-like geometry and intrinsic cavity. Yet, the role of the chirality of molecular cages in their physical properties of condensed materials, for example, the manipulation of electronic spin behaviors, remains elusive. Here, we report that chiral organic molecular cages can become an appealing chiral system to realize highly efficient spin filtering through the chirality-induced spin selectivity (CISS) effect. A pair of triphenylphosphine-containing organic cages (Pcages) with opposite handedness can manifest a very high spin polarization of nearly 90% and a high conductivity that exceeds those of other chiral molecules and structures by 2 orders of magnitude. By fabricating such molecular cages into thin-film spin filter devices, they have outstanding magnetoresistance ratios up to 12% among most of the devices based on the CISS effect. More interestingly, the Pcages can self-assemble with triphenylborane molecules through B-P frustrated Lewis acid-base complexation to form homochiral helical supramolecular nanofibrils. The spin-selective transport capacity and magnetic resistance obtained unexpected enhancement within these cage-based assemblies. This study demonstrates the potential of organic cages as a new chiral platform for controlling spin selectivity and will inspire the creation of new spintronic devices using chiral organic cage materials.