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Constructing a mixed-dimensional (MD) graphene-based van der Waals heterostructure (vdWH) is a viable technique for opening the bandgap and introducing spin polarization in graphene. In this work, we discovered that the adjacent MnF4 can manipulate the carrier doping, bandgap opening, and spin polarization of graphene in the MD vdWH of graphene/MnF4 comprised of two-dimensional (2D) graphene and one-dimensional atomic wire (1D AW) MnF4. By adopting first-principles calculations, we found that graphene can achieve effective p-type doping with the carrier density up to ∼8.89 × 1013–1.03 × 1014 cm−2. With a twisted angle of θ = 10.89° and the compressed distance of dMn-Gra = 2.84 Å, the opened bandgap of graphene (Eg-Gra) achieves 35 and 57 meV for spin-up and spin-down channels due to the sublattice symmetry-breaking in graphene, and the spin splitting energy (ΔES) at the Dirac point reaches 78.7 meV as a result of the graphene–MnF4 interlayer interaction. Remarkably, Eg-Gra is increased to 64 and 79 meV for spin-up and spin-down channels, and ΔES with 202.7 meV is obtained at dMn-Gra = 2.84 Å when the width of 1D MnF4 is doubled. Meanwhile, the n-type Ohmic contact is also realized. Our work underscores the rich interplay in the graphene/MnF4 MD vdWH and provides a significant route with fundamental insights to engineer the spintronic band properties of graphene. [ABSTRACT FROM AUTHOR]

We present detailed investigations of the magnetic properties of Pt/CoFeB/MgO layers as studied using the angle-resolved spin-torque ferromagnetic resonance method. Although the measurements provide reasonable magnetic parameters, we obtain an unusual value in the interfacial spin transparency if spin-pumping is assumed to be the dominant source for enhancing magnetic damping (αeff) in the nanometer thickness regime. However, the thickness dependence of the Landé g-factor (geff) for CoFeB indicates that the interfacial spin–orbit coupling plays a role in determining αeff. In addition, the azimuthal asymmetry in the magnetic system may not be related to the possibility of generating unconventional spin polarization. The results in this work are expected to aid in understanding various magnetic properties and current-induced spin-torques in a heavy-metal/ferromagnet bilayer. [ABSTRACT FROM AUTHOR]

We have theoretically studied spin- and valley-transport properties in a silicene quantum structure with a square magnetic barrier modulated by off-resonant circularly polarized light (OCPL). The result shows that in the magnetic quantum structure, valley and spin filtering can be realized simultaneously with appropriate OCPL at small incident angles. More interestingly, at normal incidence, Klein tunneling is observed in the K ′ valley. Besides, it is also found that valley polarization can be inverted by reversing the sign of the staggered potential or the chirality of OCPL. Nevertheless, the direction of spin polarization can only be modulated by the chirality of OCPL. These findings provide the potential applications for constructing novel type of silicene devices. [ABSTRACT FROM AUTHOR]

The two-spin solid effect (2SSE) is one of the established continuous wave dynamic nuclear polarization mechanisms that enables enhancement of nuclear magnetic resonance signals. It functions via a state-mixing mechanism that mediates the excitation of forbidden transitions in an electron–nuclear spin system. Specifically, microwave irradiation at frequencies ωμw ∼ ω0S ± ω0I, where ω0S and ω0I are electron and nuclear Larmor frequencies, respectively, yields enhanced nuclear spin polarization. Following the recent rediscovery of the three-spin solid effect (3SSE) [Tan et al., Sci. Adv. 5, eaax2743 (2019)], where the matching condition is given by ωμw = ω0S ± 2ω0I, we report here the first direct observation of the four-spin solid effect (4SSE) at ωμw = ω0S ± 3ω0I. The forbidden double- and quadruple-quantum transitions were observed in samples containing trityl radicals dispersed in a glycerol–water mixture at 0.35 T/15 MHz/9.8 GHz and 80 K. We present a derivation of the 4SSE effective Hamiltonian, matching conditions, and transition probabilities. Finally, we show that the experimental observations agree with the results from numerical simulations and analytical theory. [ABSTRACT FROM AUTHOR]

We investigate a spin-boson inspired model of electron transfer, where the diabatic coupling is given by a position-dependent phase, eiWx. We consider both equilibrium and nonequilibrium initial conditions. We show that, for this model, all equilibrium results are completely invariant to the sign of W (to infinite order). However, the nonequilibrium results do depend on the sign of W, suggesting that photo-induced electron transfer dynamics with spin–orbit coupling can exhibit electronic spin polarization (at least for some time). [ABSTRACT FROM AUTHOR]

The chiral molecules are potential generators of high spin-filters due to their inherent inversion asymmetric helical electric field. We report a controlled spin-selective transmission of electrons through self-assembled monolayers of 15 base-paired double-stranded deoxyribonucleic acid functionalized with two enantiomeric cysteine molecules on gold explored through the quantum mechanical tunneling effect. We observed a controlled spin polarization of 33% with dextro-cysteine, whereas a mere 8% was observed with levo-cysteine molecules using these functionalizations at room temperature. The manipulation of electron's spin merely through such a small molecule could lead to significant advancement in the spin-dependent charge transport phenomena and related applications. [ABSTRACT FROM AUTHOR]

A highly lattice-matched all-Heusler-alloy magnetic tunnel junction (MTJ) is proposed by associating half metallic CoFeTiSi electrode and non-magnetic semiconductor Fe2TiSi barrier. Based on the non-equilibrium Green's function combined with first-principles calculations, spin transport mechanism is studied by analyzing the transmission coefficient, local density of states, and scattering states. The calculated equilibrium tunnel magnetoresistance (TMR) ratio in CoFeTiSi/Fe2TiSi/CoFeTiSi reaches up to about 3.30 × 108%, which is much higher than in CoFeTiSi/MgO/CoFeTiSi. The calculated scattering states reveal that CoFeTiSi/Fe2TiSi/CoFeTiSi MTJ possesses two transport channels, and the contribution of channel I to the total transport is about 80%, which plays a dominate role. The analyses on non-equilibrium spin transport properties reveal that CoFeTiSi/MgO/CoFeTiSi MTJ can output a high intensity transport current with complete spin polarization, and it can output a stable and highly efficient signal. The TMR ratio possesses an extremely large value of about 2.4 × 108% and even the bias voltage increases to 0.2 V, exhibiting a robust current-driven stability. [ABSTRACT FROM AUTHOR]

Electron spin dynamics of dilute nitride GaNAs quantum well (QW)-InAs quantum dots (QDs) tunnel-coupled structures having different QW thicknesses were studied via circularly polarized time-resolved photoluminescence. The rate equation fitting considering a capture of QD electron spins by the GaNAs localized states via tunnel transfer revealed that the spin amplification dynamics of the QDs depended on the QW thickness. For the QW thickness of 5 nm, although the temporal amplification of QD electron spin polarization was slow owing to the weak wavefunction coupling between the QW and QD, the long duration of high electron spin polarization was observed because of the suppressed capture of QD majority spins relative to the efficient removal of QD minority spins. When the QW thickness increased from 5 to 20 nm, the strong spin filtering in GaNAs and strong wavefunction coupling led to the fast amplification of QD electron spin polarization with high initial spin polarization. However, the spin polarization rapidly decays after the amplification owing to the removal of both QD majority and minority spins, originating from many effective localized states. These results indicate that the time-dependent QD electron spin polarization and the resultant spin amplification can be widely tuned by changing the thickness of the tunnel-coupled GaNAs QW. [ABSTRACT FROM AUTHOR]

In the atomic cell of the spin exchange optical pumping system, the optical pumping inevitably introduces a magnetic field gradient, which affects the measurement result of the nuclear spin relaxation time a lot. To address this issue, our method achieves the measurement while excluding the influence of this magnetic field gradient. In this method, the pump laser is turned off after the spins of 87Rb and 129Xe have been effectively polarized, which results in the spin polarization of the 87Rb atoms being provided only by the spin exchange with 129Xe. Ultimately, the transverse and longitudinal components of the polarization of 129Xe are detected by the in situ87Rb atom magnetometer to obtain the T1 and T2 of 129Xe under different conditions. Using our method, since the influence of inhomogeneity caused by the pump laser is eliminated, the relaxation characteristic of atomic cells can be measured more quickly, essentially, and conveniently, which helps compare the performance of different atomic cells and find the best cell fabrication process further. [ABSTRACT FROM AUTHOR]

Recently, experimental 2D magnetic CrSe2 and CrTe2 inspired the study on their Janus CrSeTe, which breaks the mirror symmetry of Cr–Se(Te)–Cr. However, the CrSeTe monolayer possesses a lower Curie temperature and the in-plane magnetic anisotropy, and few works concerned both its zigzag- and stripy-antiferromagnetic states, which are crucial to determine the magnetic ground state and magnetic transition temperature. In this Letter, using first-principles calculations and Monte Carlo simulations, we systematically explore the strain, carrier-doping, and electric field effects on magnetic and electronic properties of monolayer CrSeTe. We demonstrate that monolayer CrSeTe preserves ferromagnetism in a large range of whether strain or doping. The estimated Curie temperature can be increased from 167 K to the room-temperature by the combination of 4% tensile strain and 0.1 e doping due to the enhanced ferromagnetic Cr–Se(Te)–Cr super-exchange interaction. Interestingly, either a small tensile strain (1%) or a low hole doping (0.025 h) can induce the transition of the easy axis from in-plane to out-of-plane due to the increased out-of-plane magnetic anisotropy from hybridized pz and py orbitals of Te atoms. In addition, the spin polarization is improved by over 60% by the tensile strain. Our results suggest that small strain and low carrier-doping induced room-temperature ferromagnetism, large out-of-plane magnetic anisotropy, and high spin polarization make CrSeTe useful in 2D spintronic applications and will stimulate broad studies on the regulation of magnetic and electronic properties of this class of magnetic Janus monolayers. [ABSTRACT FROM AUTHOR]

Spin–orbit coupling in chiral materials can induce chirality-dependent spin splitting, enabling electrical manipulation of spin polarization. Here, we use first-principles calculations to investigate the electronic states of chiral one-dimensional (1D) semiconductor InSeI, which has two enantiomorphic configurations with left- and right-handedness. We find that opposite spin states exist in the left- and right-handed 1D InSeI with significant spin splitting and spin-momentum collinear locking. Although the spin states at the conduction band minimum (CBM) and valence band maximum of 1D InSeI are both nearly degenerate, a direct-to-indirect bandgap transition occurs when a moderate tensile strain (∼4%) is applied along the 1D chain direction, leading to a sizable spin splitting (∼0.11 eV) at the CBM. These findings indicate that 1D InSeI is a promising material for chiral spintronics. [ABSTRACT FROM AUTHOR]

The Fe3GeTe2 monolayer, a ferromagnetic topological candidate with a high Curie temperature of 130 K, has recently garnered considerable interest. We investigated the impact of strain on the electronic, magnetic, and topological properties of the Fe3GeTe2 monolayer using density functional theory calculations. Our results showed that the Fe3GeTe2 monolayer was an itinerant ferromagnet with a high spin polarization of 69.93% and out-of-plane easy magnetization. Tensile strain had no profound impact on the anomalous Hall conductivity (AHC). However, when applying a compressive biaxial strain of −3%, the AHC at the Fermi level was dramatically enhanced to 1.62 e2/h, which is much larger than that of the bulk (0.7 e2/h) and bilayer (1.5 e2/h) material. The large AHC nearly coincided with the singularity of the energy bands near the M point. Our results highlight the potential of using strain engineering to control and optimize the properties of two-dimensional topological materials. [ABSTRACT FROM AUTHOR]

The magnetic field is one of the widely used external stimuli to manipulate magnetic skyrmions. On the other hand, the skyrmion Hall effect can force the skyrmion to move perpendicular to the driving direction, which may lead to the annihilation of the skyrmion at the sample edge. Here, we study a skyrmion guide based on a nanotrack, where the skyrmion is controlled by the spin-transfer torque or spin–orbit torque in the presence of an in-plane field. The effects of spin-torque parameters, spin polarization directions, and magnetic field with an appropriate magnitude on the skyrmion motion are explored. Both static and dynamic properties of the skyrmion are demonstrated through micromagnetic simulations. Our results can be useful for the development of topological transport channels for spintronic devices. [ABSTRACT FROM AUTHOR]

Thin films of ferromagnet F e 2 Ge were grown via molecular beam epitaxy, and their electrical and magneto-transport properties were measured for the first time. X-ray diffraction and vibrating sample magnetometry measurements confirmed the crystalline ferromagnetic F e 2 Ge phase. The observed high-temperature maximum in the longitudinal resistivity, as well as the observed suppression of electron–magnon scattering at low temperatures, points to the presence of strong spin polarization in this material. Measurements of the Hall resistivity, ρ x y , show contributions from both the ordinary Hall effect and the anomalous Hall effect, ρ x y A H , from which we determined the charge carrier concentration and mobility. Measurements also show a small negative magnetoresistance in both the longitudinal and transverse geometries. F e 2 Ge holds promise as a useful spintronic material, especially for its semiconductor compatibility. [ABSTRACT FROM AUTHOR]

We have developed a spin-polarized-hydrogen beam with a hexapole magnet. By combining the beam chopper and pulsed laser ionization detection, the time-of-flight of the hydrogen beam was measured, and the dependence of the beam profile on the velocity was acquired, which was consistent with the beam trajectory simulations. The spin polarization of the beam was analyzed by using the Stern–Gerlach-type magnet in combination with the spatial scan of the detection laser. The spin polarization was about 95% at a focusing condition due to the hexapole magnet. The polarization was, on the other hand, reduced to about 70% for the beam at higher velocities, which is consistent with simulation results. [ABSTRACT FROM AUTHOR]

Recently, the long-range spin-selective transport in chiral molecules has been investigated for bio-spintronics. The experimental results for a natural metalloprotein molecule suggested a high spin selectivity. I performed first-principle calculations of electron spin transport in a natural metalloprotein molecule based on the Landauer formula. A gold–metalloprotein–gold device model was used to confirm the high spin polarization. There was a relatively large spin density at some amide groups in the helical peptide structures. Furthermore, a large spin density of iron atoms enhanced the spin density of the neighboring coordinated atoms, resulting in spin polarization in the whole molecule. [ABSTRACT FROM AUTHOR]

Coupled pairs of nuclear spin-1/2 support one singlet state and three triplet states. Transitions between the singlet state and one of the triplet states may be driven by an oscillating low-frequency magnetic field, in the presence of couplings to a third nuclear spin, and a weak bias magnetic field. The oscillating field is in the same direction as the bias field and is called a WOLF (Weak Oscillating Low Field) pulse. Application of a WOLF pulse allows for the generation of strong nuclear hyperpolarization of 13C nuclei, starting from the nuclear singlet polarization of a 1H spin pair, associated with the enriched para-spin isomer of hydrogen gas. Hyperpolarization is demonstrated for two molecular systems. [ABSTRACT FROM AUTHOR]

Exploring gate insulator materials for 2D transistors and their defect properties is of importance for device performance optimization. In this work, the structural and electronic properties of intrinsic vacancies in the CaF 2 single layer and its heterostructures with monolayer MoS 2 are investigated from first-principles calculations. V Ca introduces a shallow defect level close to the VBM, whereas V F introduces a deep level below the CBM. In both cases, spin polarization is observed. Overall, V F has a relatively lower formation energy than V Ca , except for the extreme Ca-rich case. Thus, V F should be dominant in CaF 2. The band offset between CaF 2 and MoS 2 is determined to be type-I, with large offsets at both the conduction band and valence band. With the presence of vacancies in CaF 2 , the type-I band offset is preserved. The electron or hole on the defect states will transfer from CaF 2 to MoS 2 due to the large band offset, and spin polarization vanishes. Nevertheless, there are no defect states inside the gap or around the band edge of MoS 2 , and the electronic properties of MoS 2 are almost intact. Compared with h -BN that has a small valence band offset with MoS 2 and could introduce in-gap defect states, CaF 2 can be a good candidate to serve as the dielectric layer of MoS 2 -based transistors. [ABSTRACT FROM AUTHOR]

Based on the first principles of the generalized gradient approximation method, the magnetic and optical properties of Fe-, Ni-doped and (Fe,Ni) co-doped LiNbO 3 crystals are studied. The results show that the mono-doped LiNbO 3 crystals contain magnetic atoms (Fe,Ni) leading to spin polarization, and (Fe,Ni) co-doped LiNbO 3 crystals tend to the ferromagnetic state with △ E F M of − 143 meV. The total magnetic moment of the (Fe,Ni) co-doped LiNbO 3 crystal is 5.97 μ B , and the local magnetic moments of Fe and Ni are 2.99 μ B and 0.93 μ B , respectively. It is interesting that the introduction of the Ga atom makes the ferromagnetic state (△ E F M of − 285.4 meV) of the (Fe,Ni) co-doped LiNbO 3 system more stable than the anti-ferromagnetic state. Although Ga atoms do not contribute to the magnetic moment, the (Fe,Ni,Ga) co-doped LiNbO 3 is more conducive to the spin-polarized state. In addition, with the introduction of Fe, Ni, and Ga atoms, the visible region absorption changes significantly. Non-volatile holographic storage can be achieved by (Fe,Ni) co-doped LiNbO 3 , thus increasing the absorption of the visible light range. In summary, this research provides theoretical guidance for the application of LiNbO 3 crystals in spintronic devices. [ABSTRACT FROM AUTHOR]

A spintronic terahertz (THz) emitter based on rare-earth-transition-metal ferrimagnetic alloys has drawn wide attention due to its prominent THz emission signals at a magnetic compensated state. Here, THz emission spectroscopy is performed in a layered ferrimagnetic/nonmagnetic structure of Ta/Tbx(FeCo)1–x/Pt to investigate the impact of magnetization and spin polarization on THz radiation. Composition and temperature-dependent THz emission signals are observed by an inverse spin Hall effect. The variation of THz amplitude approximately follows the in-plane magnetization in the composition range, yet a nonvanishing THz radiation at the compensation point indicates that net spin polarization dominates the emitted THz electric field rather than net magnetization in this two-sublattice system. A significant gap of 90 K between the compensation point of magnetic moment and spin polarization is found in a Tb0.24(FeCo)0.76 sample, which is a striking difference to that of 25 K in GdCo/Pt THz emitters. We attribute this anomalous gap to the strong intersublattice 3d-5d6s-4f exchange interaction of TbFeCo alloy; thus, the contribution of spin polarized Tb 4f electrons should be reconsidered after fs laser pulse excitation. These results gain insight into spin dynamics of complex multisublattice systems and pave the way for further optimized spintronic THz emitters to modulate THz radiation efficiently. [ABSTRACT FROM AUTHOR]

A correlation between the spin-polarized carrier transfer and spin relaxation processes of a two-dimensional electron gas (2DEG) in an InGaN/GaN quantum well (QW) is investigated by time-resolved Kerr rotation spectroscopy at low temperature. Upon resonant excitation with the GaN barrier band edge energy, the spin polarization of the 2DEG in the QW is acquired from the transfer of spin-polarized photoexcited carriers. Significantly, the spin relaxation time of the 2DEG is enhanced to be as long as 1 ns along with the carrier transfer. It is demonstrated that by tailoring the Rashba and Dresselhaus spin–orbit couplings to approach a spin-degenerate surface, the screening effect of the polarization field leads to a longer spin relaxation time and effective manipulation of the spin relaxation. The polarization field screening induced enhancement of the spin relaxation time is significant in the way for the development of GaN-based spintronic devices. [ABSTRACT FROM AUTHOR]

Anomalous carrier transport in magnetic Heusler compounds has evolved as a lively field of research owing to their unusual band structure and broken time-reversal symmetry. They have attractive properties for spintronics due to their high Curie temperature (Tc), high spin polarization, and extravagant transport properties. Here, we scrutinize CoFeSn. Based on the inferences from structural stability, lattice dynamics, and magnetic analysis, we propose a cubic polymorph of hexagonal CoFeSn and explain why we must consider cubic CoFeSn. Through density-functional-theory calculations, we predict a robust 3D half-metallic ferromagnetic compound, CoFeSn (P 4 ¯ 3 m) with a Tc ∼ 693 K, calculated via the Heisenberg magnetic exchange interactions under mean-field approximation, and a magnetic moment of 3 μB. In addition, Wannier interpolation suggests anomalous Hall conductivity (AHC) and spin Hall conductivity (SHC) in cubic CoFeSn, the largest SHC at the Fermi level being ≈ 47 (h/2πe) S/cm. Our theoretical results show that spin–orbit interaction at the Fermi level brings on finite Berry flux that gives an intrinsic AHC ∼ 122 S/cm at room temperature. We note that adjusting the Fermi level can be a sensible way to achieve high values of AHC or SHC. Our findings pave the way for the realization of the quantum anomalous and spin Hall effect in half-Heusler compounds. [ABSTRACT FROM AUTHOR]

The investigation of spin and polarization effects in ultra-high intensity laser–plasma and laser–beam interactions has become an emergent topic in high-field science recently. In this paper, we derive a relativistic kinetic description of spin-polarized plasmas, where quantum-electrodynamics effects are taken into account via Boltzmann-type collision operators under the local constant field approximation. The emergence of anomalous precession is derived from one-loop self-energy contributions in a strong background field. We are interested, in particular, in the interplay between radiation reaction effects and the spin polarization of the radiating particles. For this, we derive equations for spin-polarized quantum radiation reaction from moments of the spin-polarized kinetic equations. By comparing with the classical theory, we identify and discuss the spin-dependent radiation reaction terms and radiative contributions to spin dynamics. [ABSTRACT FROM AUTHOR]

To meet the current requirements of diluted magnetic semiconductors (DMSs) resulting from continuous advancements in spintronics, designing d0 DMSs with high stability, spin polarization, and Curie temperature is essential. Present research on introducing d0 magnetism is limited to monatomic doping, lacking regulation measures for local magnetic moments and long range magnetic coupling. Herein, an adjacent doping strategy is employed to introduce degrees of freedom for tuning the magnetic properties of d0 DMSs. It is observed that by introducing Si and O atoms as central and adjacent dopants, respectively, the intrinsically nonmagnetic hexagonal boron nitride (h-BN) exhibits significant local magnetic moments. Furthermore, it is observed that the ionization energy, total magnetic moment, magnetic coupling, and Curie temperature of the doped h-BN are susceptible to the Si–O coordination. Subsequently, a magnetic half-metal (Si–O3-doped h-BN) with high thermal stability, 100% spin polarization, long range ferromagnetic coupling, and high Curie temperature is designed through high Si–O coordination doping. This study proposes a feasible approach for introducing tunable d0 magnetism using the design of Si–O adjacent-doped h-BN as an example. [ABSTRACT FROM AUTHOR]

2D magnetic van der Waals (vdW) junctions have attracted intensive attention due to their easily controllable thickness and clear interface compared to conventional magnetic multilayer films, which provide a perfect platform to control the performance of spintronic devices. Herein, based on the experimentally fabricated FeCl2 flaks with interlayer antiferromagnetism and intralayer ferromagnetism, we explore the spin transport properties of two classes of vdW junctions with an Au electrode, Au/FeCl2/Au (FeCl2 as the tunnel barrier) and Au/FeCl2/barrier/FeCl2/Au (MoS2 or graphene as the tunnel barrier), and focus on the effects of different barriers and the number of layers. It is found that from monolayer to bilayer FeCl2 in Au/FeCl2/Au, the spin filtering effect is considerably increased due to the weakened interface effect, and almost complete spin polarized current can be obtained. For Au/FeCl2/MoS2/FeCl2/Au, whether the number of layers of MoS2 or FeCl2 is increased from monolayer to bilayer, the tunnel magnetoresistance (TMR) becomes higher due to the high spin polarization of FeCl2, which can reach 1 374 000%. The high TMR of 763 000% can also be achieved for Au/FeCl2/graphene/FeCl2/Au. This work suggests potential applications for FeCl2 flaks in 2D vdW spin filters and spin valves and will stimulate broad studies on layer- and barrier-controllable vdW spintronic devices. All calculations are performed by using the first-principles combined with non-equilibrium Green's function method. [ABSTRACT FROM AUTHOR]

Multi-directional spin-to-charge conversion—in which spin polarizations with different orientations can be converted into a charge current in the same direction—has been demonstrated in low-symmetry materials and interfaces. This is possible because, in these systems, spin-to-charge conversion can occur in unconventional configurations in which charge current, spin current, and polarization do not need to be mutually orthogonal. Here, we explore, in the low temperature regime, the spin-to-charge conversion in heterostructures of graphene with the low-symmetry 1T' phase of MoTe2. First, we observe the emergence of charge conversion for out-of-plane spins at temperatures below 100 K. This unconventional component is allowed by the symmetries of both MoTe2 and graphene and likely arises from spin Hall effect in the spin–orbit proximitized graphene. Moreover, we examine the low-temperature evolution of non-local voltage signals arising from the charge conversion of the two in-plane spin polarizations, which have been previously observed at higher temperature. As a result, we report omni-directional spin-to-charge conversion—for all spin polarization orientations—in graphene/MoTe2 heterostructures at low temperatures. [ABSTRACT FROM AUTHOR]

Spin- and angle-resolved photoemission spectroscopy (SARPES) with high efficiency and resolution plays a crucial role in exploring the fine spin-resolved band structures of quantum materials. Here, we report the performance of the SARPES instrument with a second-generation home-made multichannel very-low-energy-electron-diffraction spin polarimeter. Its energy and angular resolutions achieve 7.2 meV and 0.52°, respectively. We present the results of SARPES measurements of Bi(111) film to demonstrate its performance. Combined with the density functional theory calculations, the spin polarization of the bulk states was confirmed by the spin-layer locking caused by the local inversion asymmetry. The surface states at a binding energy of 0.77 eV are found with 1.0 ± 0.11 spin polarization. Better resolutions and stability compared with the first-generation one provide a good platform to investigate the spin-polarized electronic states in materials. [ABSTRACT FROM AUTHOR]

A systematic structure and property investigation of MnGen− (n = 3–14) was conducted by means of density functional theory coupled with mass-selected anion photoelectron spectroscopy. This combined theoretical and experimental study allows global minimum and coexistence structures to be identified. It is found that the pentagonal bipyramid shape is the basic framework for the nascent growth process of MnGen− (n = 3–10), and from n = 10, the endohedral structures can be found. For n = 12, the anion MnGe12− cluster probably includes two isomers: a major isomer with a puckered hexagonal prism geometry and a minor isomer with a distorted icosahedron geometry. Specifically, the puckered hexagonal prism isomer follows the Wade–Mingos rules and can be suggested as a new kind of superatom with the magnetic property. Furthermore, the results of adaptive natural density partitioning and deformation density analyses suggest a polar covalent interaction between Ge and Mn for endohedral clusters of MnGe12−. The spin density and natural population analysis indicate that MnGen− clusters have high magnetic moments localized on Mn. The density of states diagram visually shows the significant spin polarization for endohedral structures and reveals the weak interaction between the Ge 4p orbital and the 4s, 3d orbitals of Mn. [ABSTRACT FROM AUTHOR]

Several proposals are available to get selective spin transmission through different nano-junctions and in all the cases the regulation is done either by applying a magnetic field or by tuning spin–orbit (SO) coupling. In the present work, we explore a separate scheme where the spin-dependent transport is regulated externally by irradiating a quantum ring that bridges the contact electrodes. This is a new proposal of generating spin selective transmission through a nano-junction, to the best of our knowledge. A high degree of spin polarization along with its phase alteration can be achieved by suitably adjusting the irradiation, circumventing the regulation of magnetic field and/or SO coupling. The effect of irradiation is included through the well-known Floquet-Bloch ansatz, where all the spin-dependent transport phenomena are worked out using Green's function formalism following the Landauer–Büttiker prescription within a tight-binding framework. Precise dependencies of light irradiation, SO coupling, magnetic flux threaded by the ring, interface sensitivity, system temperature, and impurities on spin polarization are critically investigated. Our analysis may give a new platform for spin selective electron transmission and make it applicable to other complex nano-structured materials also. We strongly believe that the present proposal can be examined in a suitable laboratory. [ABSTRACT FROM AUTHOR]

Electronic structure methods emerging from the combination of multiconfigurational wave functions and density functional theory (DFT) aim to take advantage of the strengths of the two nearly antagonistic theories. One of the common strategies employed to merge wave function theory (WFT) with DFT relies on the range separation of the Coulomb operator in which DFT functionals take care of the short-distance part, while long-range inter-electronic interactions are evaluated by using the chosen wave function method (WFT–srDFT). In this work, we uncover the limitations of WFT–srDFT in the characterization of open-shell systems. We show that spin polarization effects have a major impact on the (short-range) DFT exchange energy and are of vital importance in order to provide a balanced description between closed and open-shell configurations. We introduce different strategies to account for spin polarization in the short range based on the definition of a spin polarized electron density and with the use of short-range exact exchange. We test the performance of these approaches in the dissociation of the hydrogen molecule, the calculation of energy gaps in spin-triplet atoms and molecular diradicals, and the characterization of low-lying states of the gallium dimer. Our results indicate that the use of short-range DFT correlation in combination with a (full-range) multiconfigurational wave function might be an excellent approach for the study of open-shell molecules and largely improves the performance of WFT and WFT–srDFT. [ABSTRACT FROM AUTHOR]

We report the implementation of a Fock-operator complete-active space self-consistent field (CAS-SCF) method combined with frozen-density embedding (FDE) into the KOALA quantum-chemistry program. The implementation is based on configuration interaction from an unrestricted reference determinant and is able to treat electronic configurations such as singlet, triplet, or quintet states embedded in a molecular environment. In order to account for possible spin polarization effects, the FDE contribution is extended to the unrestricted case. We assess the convergence obtained with the implementation at the example of a stretched lithium dimer with significant multi-reference character. The efficiency of the implementation enables the orbital optimization for 25 states in a state-average SA[S0–S10,T1–T12,Q1–Q2]-CAS(10,10)-SCF calculation for the retinal molecule using a def2-TZVP basis. The FDE ansatz leads to orbitals localized by definition on the target system, thus facilitating the orbital selection required for CAS methods in complex environments. [ABSTRACT FROM AUTHOR]

The mechanism of the magnetic compass sense of migratory songbirds is thought to involve magnetically sensitive chemical reactions of light-induced radical pairs in cryptochrome proteins located in the birds' eyes. However, it is not yet clear whether this mechanism would be sensitive enough to form the basis of a viable compass. In the present work, we report spin dynamics simulations of models of cryptochrome-based radical pairs to assess whether accumulation of nuclear spin polarization in multiple photocycles could lead to significant enhancements in the sensitivity with which the proteins respond to the direction of the geomagnetic field. Although buildup of nuclear polarization appears to offer sensitivity advantages in the more idealized model systems studied, we find that these enhancements do not carry over to conditions that more closely resemble the situation thought to exist in vivo. On the basis of these simulations, we conclude that buildup of nuclear polarization seems unlikely to be a source of significant improvements in the performance of cryptochrome-based radical pair magnetoreceptors. [ABSTRACT FROM AUTHOR]

In the current stage, valley-contrasting physics is mainly rooted in nonmagnetic and/or ferromagnetic hexagonal lattices and is rarely used to observe the simultaneous spin and valley polarization in antiferromagnetic materials. In this work, we propose a general scheme that can be achieved easily in experiments to break the P T joint symmetry of antiferromagnetic structures, that is, introducing an out-of-plane potential gradient to realize spin–valley splitting and spontaneous valley polarization. In combination of the model analysis and first-principles calculations, we translate the concept into Mn2P2X3Y3 monolayers and clarify the valley-related physics. It is obvious that our finding significantly extends the scope of valleytronics in both theory and experiments. [ABSTRACT FROM AUTHOR]

Electric-field control of spin polarization of electrons during injection into InGaAs quantum dots (QDs) was studied via circularly polarized time-resolved photoluminescence. Electric-field modulation of optical spin polarization in QDs will play a key role in future progress of semiconductor opto-spintronics. The tuning of band potentials by applying external electric fields can not only affect spin-injection efficiencies but also switch dominant spin-injection layers. In this study, we developed a QD-based electric-field-effect optical spin device with two different spin-injection layers, which consisted of a GaAs and GaAs/Al0.15Ga0.85As superlattice (SL) barriers. The bias-voltage modulation of the optical spin polarization in QDs was demonstrated by changing the spin polarization degree of electrons injected from these barriers into the QD via the electric-field switching of the spin-injection layers. This was achieved by exploiting the difference in spin relaxation properties between bulk GaAs and the SL. This proposed structure, which comprised of one luminescent layer and two spin-injection layers, is highly scalable because the modulation range of optical spin polarization can be enhanced by changing the combination of spin-injection layers, as well as the material used and its layer thickness. [ABSTRACT FROM AUTHOR]

The robustness of spin–orbit torque (SOT) induced magnetization switching and ease of deposition make type-X devices, where the in-plane easy axis lies perpendicular to the spin polarization, attractive in the field of spintronics. However, universally applicable and straightforward detection of type-X magnetization reversal is still elusive, unlike type-Z switching, which employs DC-based anomalous Hall effect measurement. Here, we demonstrated that the odd planar Hall voltage (O-PHV) signal exhibits an odd symmetry with the application of an external magnetic field which motivates us to develop a reading mechanism for detecting magnetization switching of in-plane magnetized type-X devices. We verified our DC-based reading mechanism in the Pt/Co/NiFe/Pt stack where a thin Co layer is inserted to create dissimilar interfaces about the NiFe layer. Remarkably, the current-induced in-plane fields are found to be significantly large in Pt/Co/NiFe/Pt stack. Furthermore, we employed the O-PHV method to detect the current-induced magnetization switching. The pure DC nature of the writing and reading mechanism of our proposed type-X detection technique through O-PHV makes it the easiest in-plane magnetization detection technique. Moreover, the high repeatability and easy detection of our proposed method will open avenues toward in-plane SOT switching based memory devices and sensors. [ABSTRACT FROM AUTHOR]

Recently, band-splitting associated with spin polarization at K- and K′-points of the Brillouin zone has been found in centrosymmetric transition metal dichalcogenide materials. This discovery offers a possibility on centrosymmetric crystals for potential valleytronic applications. However, the origin of the band-splitting and the spin polarization in multilayer and bulk transition metal dichalcogenides remains unclear as the interlayer coupling should play a role when compared with that in monolayers. Here, by performing spin- and angle-resolved photoemission spectroscopy in bulk 2H-WSe2 at variable temperatures, we have quantitatively established contributions of the intralayer spin–orbit coupling and interlayer coupling. While the strength of the intralayer spin–orbit coupling is determined to be 450 meV, independent of the temperature, the strength of the interlayer coupling is found to increase from 68 to 172 meV as the temperature decreases from 300 to 80 K. This is also accompanied by an increase in the total band-splitting and a decrease in the spin polarization. This work reveals the micro-mechanism of spin and interlayer interaction in centrosymmetric materials, which provides a basis for the development of next-generation energy-efficient valleytronic devices. [ABSTRACT FROM AUTHOR]

Heusler magnetic alloys offer a wide variety of electronic properties very promising for spintronics and magnonics. Some alloys exhibit a spin gap in their band structure at the Fermi energy, the so-called half-metal magnetic (HMM) behavior. This particular property leads to two very interesting properties for spintronics, i.e., fully polarized current together with ultra-low magnetic damping, two key points for spin-transfer-torque based devices. This Tutorial gives experimental details to grow and characterize Heusler Co2MnZ compounds in thin films (Z = Al, Si, Ga, Ge, Sn, Sb) by using molecular beam epitaxy in order to get the proper predicted electronic properties. A first part of this Tutorial is dedicated to control the stoichiometry as best as possible with some methods to test it. The chemical ordering within the lattice was examined by using electron diffraction during growth, regular x-ray diffraction, and scanning transmission electron microscopy. In particular, standard x-ray diffraction is carefully analyzed depending on the chemical ordering in the cubic cell and shown to be inefficient to distinguish several possible phases, on the contrary to electron microscopy. The electronic properties, i.e., magnetic moment, spin polarization, and magnetic damping were reviewed and discussed according to the stoichiometry of the films and also theoretical predictions. Polycrystalline films were also analyzed, and we show that the peculiar HMM properties are not destroyed, a good news for applications. A clear correlation between the spin polarization and the magnetic damping is experimentally demonstrated. At least, our study highlights the major role of stoichiometry on the expected properties. [ABSTRACT FROM AUTHOR]

Magnetic nanocomposites based on MnAs clusters embedded in a chalcopyrite host usually do not exhibit large magnetoresistance (MR) at room temperature, while pronounced effects are localized at very low temperatures. In the present work, we observed an appearance of large pressure-induced negative and positive MR at room temperature in the Zn0.1Cd0.9GeAs2 hybrid system containing 10% MnAs inclusions. With the applied pressure, a substantial modification of the electron transport from semimetallic to semiconducting type occurs, followed by a subsequent structural transition at P ≈ 3.5 GPa into almost metallic high-pressure phase. This picture is simultaneously supported by temperature-dependent and room temperature high-pressure transport measurements. Using a semiempirical expression, taking into account a spin-dependent scattering of charge carriers due to MnAs nanoclusters, as well as a two-band conductivity model, we have been able to partially describe the observed MR effects. The predominantly weak positive contribution at P = 1 GPa, which is well described in the framework of the proposed approach indicates the presence of spin-polarized charge carriers. Based on the two-band model calculations, a negative spin polarization was found at P ≥ 3 GPa that ascribed to a structural change of the matrix. As our results indicate, an emerging MR in the structural transition region is characterized by a complex behavior. In particular, the negative part of MR demonstrates a magnetic field dependence different than Δρ/ρ0 ∼ H2, suggesting the presence of unusual scattering mechanisms in magnetotransport. [ABSTRACT FROM AUTHOR]

Broken-symmetry calculations of diradicals exploit the mean-field energies of determinants that are not eigenfunctions of the Ŝ 2 operator, the mean value of which is close to 1 for the ms = 0 solution. This spin contamination must be corrected. Two different contributions affect ⟨ Ŝ 2 ⟩ , namely, the mixing between neutral and ionic valence bond components, the so-called kinetic exchange, which decreases ⟨ Ŝ 2 ⟩ , and the spin polarization of the supposedly closed shell orbitals, which increases ⟨ Ŝ 2 ⟩. The popular Yamaguchi formula is valid for the first effect but irrelevant for the second one. From a few constrained broken-symmetry calculations, one may treat separately the two contributions and apply their specific spin decontamination correction. This work proposes a consistent spin-decontaminated procedure for the evaluation of singlet–triplet gaps in diradicals. [ABSTRACT FROM AUTHOR]

A perylene (Pery)–phenoxazine (PXZ) compact orthogonal electron donor/acceptor dyad was prepared to study the relationship between the molecular structures and the spin–orbit charge transfer intersystem crossing (SOCT-ISC), as well as the electron spin selectivity of the ISC process. The geometry of Pery–PXZ (80.0°) is different from the previously reported perylene–phenothiazine dyad (Pery–PTZ, 91.5°), although there is only one atom variation for the two dyads. Pery–PXZ shows a high singlet oxygen quantum yield (84%). Femtosecond transient absorption spectra indicate that the charge separation (CS, faster than 120 fs) is faster than the Pery–PTZ analog (CS, 250 fs) and charge recombination (CR, i.e., SOCT-ISC, 5.98 ns) of Pery–PXZ is slower than the Pery–PTZ analog (CR, 0.9 ns). The intrinsic triplet state lifetime of Pery–PXZ is 242 µs vs the lifetime of 181 µs for the Pery–PTZ analog. Moreover, the triplet state lifetime of Pery–PXZ in the solid polymer matrix is extended to 4.45 ms, which indicates that the triplet state of Pery–PXZ in fluid solution is deactivated not only by the triplet–triplet annihilation effect but also by other factors such as vibration coupled relaxation. Interestingly, with pulsed laser excited time-resolved electron paramagnetic resonance spectroscopy, the electron spin polarization (ESP) pattern of the triplet state of the current dyad is opposite to that of Pery–PTZ. These results demonstrated the rich electron spin chemistry of the ISC of compact electron donor/acceptor dyads, e.g., the ESP is dependent on not only the molecular geometry but also the structure of the electron donor (or acceptor). [ABSTRACT FROM AUTHOR]

To investigate the effects of the optical field and the Fermi velocity on the transport properties of spin and valley electrons, we impose a normal/ferromagnetic/normal (N/F/N) quantum structure based on the monolayer WSe 2. The results indicate that there is a strong switch effect for spin- and valley-related electrons. When left-handed off-resonant circularly polarized light is irradiated in the intermediate ferromagnetic region, 100 % polarization for K valley electrons can be achieved in the entire effective energy spectrum of the optical field. Meanwhile, 100 % polarization of the K ′ valley can also be gained with the right-handed off-resonant circularly polarized light in the junction. Moreover, the perfect polarization of spin-up electrons can be obtained when the ferromagnetic exchange field is applied to the structure. Additionally, the Fermi velocity barrier also changes the energy band of the studied material, which makes the spin and valley transport increase with the increase of the velocity barrier but does not produce spin or valley polarizations. These interesting results clarify that the optical field and the Fermi velocity both make a contribution to the modulation of spin electrons for the two valleys and provide a useful method for the design of novel spintronic and valleytronic devices. [ABSTRACT FROM AUTHOR]

Compared with conventional magnetic ways, modulating a spin-polarized current through electrical means could greatly reduce nano-devices' energy consumption and dimensions, which emerges as a new research area in spintronics. Inspired by the experimental progress on the synthesis of helically twisted graphene, we study the electronic transport of kekulene-like helical graphene nanoribbons through first-principles calculations. By applying a gate voltage, the system can be switched between spin-unpolarized and completely spin-polarized states, realizing an electrically controlled spin filter. Moreover, a fine modulation of the spin polarization can also be achieved, where transmission with any ratio of spin-up to spin-down electrons can be obtained, beyond the traditional spin filter. The analysis shows that it is the particular transmission spectra that play a key role, where two wide peaks with opposite spins reside partially overlapped around the Fermi level. They originate from the p orbitals of the zigzag edge part in the helical structure. Since the configuration only consists of carbon atoms, the electrical control of spin polarization is realized in a pure-carbon nano-system, showing great application potentials. [ABSTRACT FROM AUTHOR]

Intercalation offers a promising way to alter the physical properties of two-dimensional (2D) layered materials. Here, we investigate the electronic and vibrational properties of 2D layered MoSe2 intercalated with atomic manganese at ambient and high pressure up to 7 GPa by Raman scattering and electronic structure calculations. The behavior of optical phonons is studied experimentally with a diamond anvil cell and computationally through density functional theory calculations. Experiment and theory show excellent agreement in optical phonon behavior. The previously Raman inactive A2u mode is activated and enhanced with intercalation and pressure, and a new Raman mode appears upon decompression, indicating a possible onset of a localized structural transition, involving the bonding or trapping of the intercalant in 2D layered materials. Density functional theory calculations reveal a shift of the Fermi level into the conduction band and spin polarization in MnxMoSe2 that increases at low Mn concentrations and low pressure. Our results suggest that intercalation and pressurization of van der Waals materials may allow one to obtain dilute magnetic semiconductors with controllable properties, providing a viable route for the development of new materials for spintronic applications. [ABSTRACT FROM AUTHOR]

Half-metallic Heusler alloys have been intensively studied in recent years due to their potential applications in spin-based devices, e.g., in magnetic tunnel junctions. Yet, their properties may be very sensitive to the choice of the substrates, i.e., to the epitaxial strain and interface properties. Here, we report the results of our computational work on the half-Heusler compound CrMnSb(1−x)Px. In particular, we demonstrate that the parent compound CrMnSb is close to a half-metallic material at the optimized lattice parameter, with the onset of the half-metallic bandgap a few meV above the Fermi energy. Moreover, although it undergoes a half-metallic transition under a uniform compression of ∼1.5%, such a transition is absent under epitaxial strain. At the same time, we show that a half-metallic transition could be induced by a chemical substitution of Sb with P, which results in a volume reduction of the unit cell. In particular, 50% substitution of Sb with P leads to a robust half-metallicity in CrMnSb(1−x)Px, with 100% spin polarization being retained at a large range of epitaxial strain. Thus, our results indicate that CrMnSb0.5P0.5 could be grown on different types of substrates, e.g., GaAs, without its electronic properties being detrimentally affected by biaxial strain. In addition, CrMnSb0.5P0.5 exhibits a fully compensated ferrimagnetic alignment, which could be potentially useful in applications where stray magnetic fields are undesirable. [ABSTRACT FROM AUTHOR]

The effect of reversible energy hopping between different local environments on the properties of spin-polarized excited states is investigated theoretically using a two-site model. The kinetic equations for the populations of the spin sublevels of the excited state are derived and then used to obtain analytical expressions for the evolution of the spin polarization of excited triplet states under specific conditions. The time dependence of the triplet state polarization patterns is also obtained by numerical solution of the kinetic equations. It is shown that the reversible energy hopping can lead to significant changes in the properties of the triplet state, including changes in the shape of the observed spectrum and, in some cases, the inversion of the sign of the polarization, the generation of the net polarization, and anisotropic spin-lattice relaxation. The relations between the parameters that can be observed experimentally by time-resolved electron paramagnetic resonance spectroscopy and the kinetic and dynamic parameters of the system are discussed. [ABSTRACT FROM AUTHOR]

Spin-polarization effects may play an important role in free radicals and in the magnetic coupling between radical centers. Starting from restricted open-shell calculations, i.e., a closed-shell description of the non-magnetic core electrons, a low-order perturbation expansion identifies the spin-polarization contribution to the energy of mono-radicals and to singlet–triplet energy differences in diradicals. Broken-symmetry (BS) single-determinant calculations introduce only a fraction of spin-polarization effects, and in a biased manner, since BS determinants are not spin eigenfunctions. We propose a simple technique to correctly evaluate spin-polarization energies by taking into account the effect of spin-flip components on one-hole one-particle excited configurations. Spin-decontamination corrections are shown to play a non-negligible role in the BS evaluation of bond energies. The importance of spin decontamination is illustrated in cases for which spin polarization is the leading contribution to the singlet–triplet gap, which characterizes twisted conjugated double bonds and disjoint diradicals. [ABSTRACT FROM AUTHOR]

Taking as an example the simple CH3 radical, this work demonstrates the cooperative character of the spin-polarization phenomenon of the closed-shell core in free radicals. Spin polarization of CH σ bonds is not additive here, as spin polarization of one bond enhances that of the next bond. This cooperativity is demonstrated by a series of configuration interaction calculations converging to the full valence limit and is rationalized by analytic developments. The same phenomenon is shown to take place in those diradicals where spin polarization plays a major role, as illustrated in square planar carbo-cyclobutadiene C12H4. The treatment of cooperativity represents a challenge for usual post-Hatree–Fock methods. [ABSTRACT FROM AUTHOR]