Spin Direction Research Articles

Qubits based on merons in magnetic nanodisks

A meron is a classical topological soliton having a half topological charge. It could be materialized in a magnetic disk. However, it will become a quantum mechanical object when its size is of the order of nanometers. Here, we propose to use a nanoscale meron in a magnetic nanodisk as a qubit, where the up and down directions of the core spin are assigned to be the qubit states leftvert 0rightrangle and leftvert 1rightrangle. We first numerically show that a meron with the radius containing as small as 7 spins can be stabilized in a ferromagnetic nanodisk classically. Then, we show theoretically that universal quantum computation is possible based on merons by explicitly constructing the arbitrary phase-shift gate, Hadamard gate, and CNOT gate. They are executed by applying a magnetic field or spin-polarized current. Our results may be useful for the implementation of quantum computation based on topological spin textures in nanomagnets.

Field-Free-Switching State Diagram of Perpendicular Magnetization Subjected to Conventional and Unconventional Spin-Orbit Torques

The lack of certain crystalline symmetries in strong spin-orbit-coupled nonmagnetic materials allows for the existence of unconventional spin Hall responses, with electrically generated transverse spin currents possessing collinear flow and spin directions. The injection of such spin currents into an adjacent ferromagnetic layer can excite magnetization dynamics via unconventional spin-orbit torques, leading to deterministic switching in ferromagnets with perpendicular magnetic anisotropy. We study the interplay between conventional and unconventional spin-orbit torques on the magnetization dynamics of a perpendicular ferromagnet in the small intrinsic damping limit, and identify a rich set of dynamical regimes that includes deterministic and probabilistic switching, precessional and pinning states. Contrary to common belief, we find that there exists a critical conventional spin Hall angle, beyond which deterministic magnetization switching transitions to a precessional or pinned state. Conversely, we show that larger unconventional spin Hall angle is generally beneficial for deterministic switching. We derive an approximate expression that qualitatively describes the state-diagram boundary between the full deterministic switching and precessional states and discuss a criterion for searching symmetry-broken spin Hall materials in order to maximize switching efficiency. Our work offers a roadmap towards energy-efficient spintronic devices, which might open the door for applications in advanced in-memory computing technologies.

Fast broadband cluster spin-glass dynamics in PbFe1/2Nb1/2O3

PbFe$_{1/2}$Nb$_{1/2}$O$_{3}$ (PFN) is a relaxor ferroelectric (T$_{c}$ $\sim$ 400 K) consisting of disordered magnetic Fe$^{3+}$ (S=${5\over2}$, L$\approx$0) ions resulting in a low temperature ``cluster glass" phase (W. Kleemann $\textit{et al.}$ Phys. Rev. Lett. ${\bf{105}}$, 257202 (2010)). We apply neutron scattering to investigate the dynamic magnetism of this phase in a large single crystal which displays a low temperature spin glass transition (T$_{g} \sim$ 15 K), but no observable spatially long-range antiferromagnetic order. The static response in the cluster glass phase (sampled on the timescale set by our resolution) is found to be characterized by an average magnetic spin direction that lacks any preferred direction. The dynamics that drive this phase are defined by a magnetic correlation length that gradually increases with decreasing temperature. However, below $\sim$ 50 K the spatial correlations gradually becoming more short range indicative of increasing disorder on cooling, thereby unravelling magnetism, until the low temperature glass phase sets in at T$_{g}$ $\sim$ 15 K. Neutron spectroscopy is used to characterize the spin fluctuations in the cluster glass phase and are found to be defined by a broadband of frequencies on the scale of $\sim$ THz, termed here ``fast" fluctuations. The frequency bandwidth driving the magnetic fluctuations mimics the correlation length and decreases until $\sim$ 50 K, and then increases again until the glass transition. Through investigating the low-energy acoustic phonons we find evidence of multiple distinct structural regions which form the basis of the clusters, generating a significant amount of local disorder. We suggest that random molecular fields originating from conflicting interactions between clusters is important for the destruction of magnetic order and the eventual formation of the cluster glass in PFN.

Tomographic reconstruction of an azimuthally forced flame in an annular chamber

Azimuthally forced spinning modes on a single ethylene-air swirl flame in an annular combustor were investigated using phase-averaged three-dimensional (3D) Computed Tomography of Chemiluminescence. Strongly spinning azimuthal modes in the clockwise (CW) and anticlockwise (ACW) directions were introduced by means of carefully controlled acoustic forcing. Tomographic reconstructions were calculated based on 25 independent views for an unforced, and CW and ACW forced cases. Using only a single flame in an annular enclosure resulted in a flame shape that differed from previous multi-flame investigations. The flame experiences significantly less flame-wall and no flame-flame interactions. Results at high and low equivalence ratio indicate that in the absence of significant enclosure effects, the global heat release rate (HRR) response is the same for both forcing directions. The 3D HRR oscillation distributions were investigated in detail, and the local flame response to modes with opposite spin direction was shown to feature 180∘ rotational symmetry. High magnitude HRR oscillations are formed close to the flame base, but due to the combined azimuthal and axial excitation the response on one side of the flame is significantly higher in magnitude, and concentrations of HRR oscillations are seen close to the inner or outer annular walls during CW or ACW excitation respectively. Swirl also causes these high magnitude structures to rotate slowly with downstream distance, although the spatial redistribution of HRR oscillations through this effect is subtle. This improves our physical understanding of previous observations of differing global flame responses to CW and ACW azimuthal excitation.

Spin‐Controlled Reconfigurable Excitations of Spoof Surface Plasmon Polaritons by a Compact Structure

AbstractThe photonic spin Hall effect (SHE) arises from the spin–orbit interaction of lights and plays an important role in light–matter interactions. The phenomenon of spin‐momentum locking validates photonic SHE with unprecedented abilities in wave manipulation. Here, the directional coupling and spin‐momentum locking in spoof surface plasmon polaritons (SSPP) are demonstrated. The transverse spin angular momentum in SSPP is calculated using effective medium theory and the study shows the spin direction is inherently locked to the propagation direction, thus manifesting the spin–orbit interaction of electromagnetic (EM) waves. The spin‐momentum locking is further verified by projecting linearly and circularly polarized waves onto a scatterer‐SSPP structure. It is observed that the helicity of the incident EM wave governs the propagation direction of excited SSPP modes and the directional coupling originates from constructive and destructive interferences of two orthogonal modes. Reconfigurable transmissions of SSPPs are further demonstrated. The proposed design can find applications in reconfigurable sensors, antennas, and power dividers. This approach demonstrates the spin‐momentum locking in SSPPs and introduces new degrees of freedom to manipulate SSPPs by engineering the helicity and interference of EM waves.

Almost Perfect Spin Filtering in Graphene-Based Magnetic Tunnel Junctions.

We report on large spin-filtering effects in epitaxial graphene-based spin valves, strongly enhanced in our specific multilayer case. Our results were obtained by the effective association of chemical vapor deposited (CVD) multilayer graphene with a high quality epitaxial Ni(111) ferromagnetic spin source. We highlight that the Ni(111) spin source electrode crystallinity and metallic state are preserved and stabilized by multilayer graphene CVD growth. Complete nanometric spin valve junctions are fabricated using a local probe indentation process, and spin properties are extracted from the graphene-protected ferromagnetic electrode through the use of a reference Al2O3/Co spin analyzer. Strikingly, spin-transport measurements in these structures give rise to large negative tunnel magneto-resistance TMR = −160%, pointing to a particularly large spin polarization for the Ni(111)/Gr interface PNi/Gr, evaluated up to −98%. We then discuss an emerging physical picture of graphene–ferromagnet systems, sustained both by experimental data and ab initio calculations, intimately combining efficient spin filtering effects arising (i) from the bulk band structure of the graphene layers purifying the extracted spin direction, (ii) from the hybridization effects modulating the amplitude of spin polarized scattering states over the first few graphene layers at the interface, and (iii) from the epitaxial interfacial matching of the graphene layers with the spin-polarized Ni surface selecting well-defined spin polarized channels. Importantly, these main spin selection effects are shown to be either cooperating or competing, explaining why our transport results were not observed before. Overall, this study unveils a path to harness the full potential of low Resitance.Area (RA) graphene interfaces in efficient spin-based devices.

Analysis of spin directions of galaxies in the DESI Legacy Survey

ABSTRACT The DESI Legacy Survey is a digital sky survey with a large footprint compared to other Earth-based surveys, covering both the Northern and Southern hemispheres. This paper shows the distribution of the spin directions of spiral galaxies imaged by DESI Legacy Survey. A simple analysis of dividing nearly 1.3 × 106 spiral galaxies into two hemispheres shows a higher number of galaxies spinning counterclockwise in the Northern hemisphere, and a higher number of galaxies spinning clockwise in the Southern hemisphere. That distribution is consistent with previous observations, but uses a far larger number of galaxies and a larger footprint. The larger footprint allows a comprehensive analysis without the need to fit the distribution into an a priori model, making this study different from all previous analyses of this kind. Fitting the spin directions of the galaxies to cosine dependence shows a dipole axis alignment with probability of P < 10−5. The analysis is done with a trivial selection of the galaxies, as well as simple explainable annotation algorithm that does not make use of any form of machine learning, deep learning, or pattern recognition. While further work will be required, these results are aligned with previous studies suggesting the possibility of a large-scale alignment of galaxy angular momentum.

Magneto-optical Kerr effect and magnetoelasticity in a weakly ferromagnetic RuF4 monolayer

Considerable research interest has been attracted to noncollinear magnetic structures for their intriguing physics and promising applications. In this work, based on relativistic density functional theory, we reveal the interesting magnetic order and relevant properties in monolayer ${\mathrm{RuF}}_{4}$, which can be exfoliated from its bulk phase. Although the spins on Ru ions are almost antiferromagnetically aligned between nearest neighbors, weak ferromagnetism is generated because of the antisymmetric Dzyaloshinskii-Moriya interaction as well as the single-ion anisotropy. A prominent magneto-optical Kerr effect can be observed for this antiferromagnet, similar to those of regular strong ferromagnets. In addition, a uniaxial strain can induce a ferroelastic switching together with the in-plane rotation of spin direction, giving rise to a strong intrinsic magnetoelasticity. Our work not only suggests an alternative direction for two-dimensional magnetic materials, but also provides hints to future devices based on antiferromagnetic magnetoelastic or magneto-optical materials.

Multiple dimensions of spin-gapless semiconducting states in tetragonal Sr2CuF6

Spin-gapless semiconductors (SGSs), with intrinsic magnetism, $100%$ spin polarization, and zero-gap band crossing points, have attracted great scientific interest owing to their potential applications in spintronics. In this Letter, using first-principles calculations and symmetry analysis, we demonstrate that the realistic material ${\mathrm{Sr}}_{2}{\mathrm{CuF}}_{6}$ is a spintronic material with multiple dimensions of spin-gapless semiconducting states. Tetragonal ${\mathrm{Sr}}_{2}{\mathrm{CuF}}_{6}$ has a zero-dimensional zero-gap nodal point, a one-dimensional zero-gap nodal line, and a two-dimensional nearly zero-gap nodal surface in one spin direction. Moreover, it hosts a wide band gap in the other spin direction. Our results extend the SGS members from nodal point SGSs and nodal line SGSs to nodal surface SGSs. Furthermore, we report a SGS candidate in an experimentally realized material exhibiting different dimensions of zero-gap points in momentum space. It is hoped that spintronic materials with multiple dimensions of spin-gapless semiconducting states may have significant applications in new-generation spintronics.

Reversed spin of a ratchet motor on a vibrating water bed

A ratchet gear on a vibrating water bed exhibits a one-way spin. However, the spinning direction is opposite to that of the gear placed on the granular bed. The one-way spin is caused by the surface waves of water. Surface deformation causes transportation of the water element to rotate the gear. The spatial symmetry of the surface wave and gear geometry regulates the rotational torque. In this study, the same ratchet shows reversed motion between the granular and water beds, and the direction is not determined only by the ratchet geometry. The self-organization of the fluid medium caused by small agitation induces a nontrivial inversion of the spinning direction.

Control of electron beam polarization in the bubble regime of laser-wakefield acceleration

Electron beam polarization in the bubble regime of the interaction between a high-intensity laser and a longitudinally pre-polarized plasma is investigated by means of the Thomas–Bargmann–Michel–Telegdi equation. Using a test-particle model, the dependence of the accelerated electron polarization on the bubble geometry is analysed in detail. Tracking the polarization dynamics of individual electrons reveals that although the spin direction changes during both the self-injection process and acceleration phase, the former has the biggest impact. For nearly spherical bubbles, the polarization of electron beam persists after capture and acceleration in the bubble. By contrast, for aspherical bubble shapes, the electron beam becomes rapidly depolarized, and the net polarization direction can even reverse in the case of a oblate spheroidal bubble. These findings are confirmed via particle-in-cell simulations.

Unexpected Dancing Partners: Tracing the Coherence between the Spin and Motion of Dark Matter Halos

A recent study conducted using CALIFA survey data has found that the orbital motions of neighbor galaxies are coherent with the spin direction of a target galaxy on scales of many megaparsecs. We study this so-called “large-scale coherence” phenomenon using N-body cosmological simulations. We confirm a strong coherence signal within 1 Mpc h −1 of a target galaxy, reaching out to 6 Mpc h −1. We divide the simulation halos into subsamples based on mass, spin, merger history, and local halo number density for both target and neighbor halos. We find a clear dependency on the mass of the target halo only. Another key parameter is the local number density of both target and neighbor halos, with high-density regions such as clusters and groups providing the strongest coherence signals, rather than filaments or lower-density regions. However we do not find a clear dependency on halo spin or time since last major merger. The most striking result we find is that the signal can be detected up to 15 Mpc h −1 from massive halos. These results provide valuable lessons on how observational studies could more clearly detect coherence, and we discuss the implications of our results for the origins of large-scale coherence.

Asymmetry in Galaxy Spin Directions—Analysis of Data from DES and Comparison to Four Other Sky Surveys

The paper shows an analysis of the large-scale distribution of galaxy spin directions of 739,286 galaxies imaged by DES. The distribution of the spin directions of the galaxies exhibits a large-scale dipole axis. Comparison of the location of the dipole axis to a similar analysis with data from SDSS, Pan-STARRS, and DESI Legacy Survey shows that all sky surveys exhibit dipole axes within 52° or less from each other, well within 1σ error, while non-random distribution is unexpected, the findings are consistent across all sky surveys, regardless of the telescope or whether the data were annotated manually or automatically. Possible errors that can lead to the observation are discussed. The paper also discusses previous studies showing opposite conclusions and analyzes the decisions that led to these results. Although the observation is provocative, and further research will be required, the existing evidence justifies considering the contention that galaxy spin directions as observed from Earth are not necessarily randomly distributed. Possible explanations can be related to mature cosmological theories, but also to the internal structure of galaxies.

Using 3D and 2D analysis for analyzing large-scale asymmetry in galaxy spin directions

Abstract The nature of galaxy spin is still not fully known. Iye, Yagi, and Fukumoto (2021, AJ, 907, 123) applied a 3D analysis to a dataset of bright SDSS galaxies that was used in the past for photometric analysis. They showed that the distribution of spin directions of spiral galaxies is random, providing a dipole axis with low statistical significance of 0.29σ. However, to show random distribution, two decisions were made, each of which can lead to random distribution regardless of the real distribution of the spin direction of galaxies. The first decision was to limit the dataset arbitrarily to z < 0.1, which is a redshift range in which previous literature already showed that random distribution is expected. More importantly, while the 3D analysis requires the redshift of each galaxy, the analysis was done with the photometric redshift. If the asymmetry existed, its signal is expected to be an order of magnitude weaker than the error of the photometric redshift, and therefore a low statistical signal under these conditions is expected. When using the exact same data without limiting to zphot < 0.1 and without using the photometric redshift, the distribution of the spin directions in that dataset shows a statistical signal of >2σ. Code and data for reproducing the analysis are publicly available. These results are in agreement with other experiments with SDSS, Pan-STARRS, HST, and the DESI Legacy Survey. The paper also examines other previous studies that showed random distribution in galaxy spin directions. While further research will be required, the current evidence suggests that large-scale asymmetry between the number of clockwise and counterclockwise galaxies cannot be ruled out.

Direct Atomic Observation of Reversible Orientation Switch in Monoatomic-Layered Gold Membrane Conducted by Dynamic Vortex.

Controlling the material structure at an atomic scale to tune their physicochemical and nanoengineering properties is a major driving force of nanotechnology. However, manipulating the structural variation in monoatomic-layered metals remains a challenge, hindering the full application of their novel properties. Here, we show by experiments and simulations that a reversible orientation rotation of monoatomic-layered gold membrane embedded in the gold crystal is performed through dynamic vortexing that is comprised of the circular motion of atoms. A pair of dynamic vortices are successively generated and together span the entire gold membrane to accomplish the orientation switch. Density functional theory calculations demonstrate that the gold membrane exhibits a Rashba-type spin splitting, while the spin direction reversibly flips with the switching orientation of the gold membrane. The results provide a conceptual approach for constructing a novel electronic system with monoatomic-layered metals and the reversible spin-flip has inspiring applications for future spintronics.

Fluctuating spin-orbital texture of Rashba-split surface states in real and reciprocal space

Spin-orbit interaction (SOI) in low-dimensional systems, namely Rashba systems and the edge states of topological materials, is extensively studied in this decade as a promising source to realize various fascinating spintronic phenomena, such as the source of the spin current and spin-mediated energy conversion. Here, we show the odd fluctuation in the spin-orbital texture in a surface Rashba system on Bi/InAs(110)-(2$\times$1) by spin- and angle-resolved photoelectron spectroscopy and a numerical simulation based on a density-functional theory (DFT) calculation. The surface state shows a paired parabolic dispersion with the spin degeneracy lifted by the Rashba effect. Although its spin polarization should be fixed in a particular direction based on the Rashba model, the observed spin polarization varies greatly and even reverses its sign depending on the wavenumber. DFT calculations also reveal that the spin directions of two inequivalent Bi chains on the surface change from nearly parallel (canted-parallel) to anti-parallel in real space in the corresponding wavevector region. These results point out an oversimplification of the nature of spin in Rashba and Dirac systems and provide more freedom than expected for spin manipulation of photoelectrons.

Bipolar Magnetic Molecules for Spin‐Polarized Electric Current in Molecular Junctions

AbstractElectrical control of spin transport at single molecule level is highly desired for molecular nanospintronics. By exploiting magnetic bistability of spin crossover complexes, the magnitude of spin polarization can be modulated. However, efficiently controlling the direction of spin polarization at single molecule level is still challenging. Here, we propose a general method to flip the transport electron spin simply by electrical gating in single molecule devices based on bipolar magnetic molecules (BMMs), of which the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) come from different spin channels. Thus, when the device's Fermi level is reversibly adjusted approaching either HOMO or LUMO by changing the polarity of the applied voltage gate, a 100 % spin polarized current with switchable spin direction is achievable. The proposed method is verified by the calculated electronic and transport properties of 9 potential transition metal coordination BMMs.

Bipolar Magnetic Molecules for Spin-Polarized Electric Current in Molecular Junctions.

Electrical control of spin transport at single molecule level is highly desired for molecular nanospintronics. By exploiting magnetic bistability of spin crossover complexes, the magnitude of spin polarization can be modulated. However, efficiently controlling the direction of spin polarization at single molecule level is still challenging. Here, we propose a general method to flip the transport electron spin simply by electrical gating in single molecule devices based on bipolar magnetic molecules (BMMs), of which the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) come from different spin channels. Thus, when the device's Fermi level is reversibly adjusted approaching either HOMO or LUMO by changing the polarity of the applied voltage gate, a 100 % spin polarized current with switchable spin direction is achievable. The proposed method is verified by the calculated electronic and transport properties of 9 potential transition metal coordination BMMs.

Physics of manipulation of spin dynamics in a driven double well made transparent

We study the coherent manipulation of quantum spin dynamics via simple analytic solutions for a spin–orbit (SO) coupled ultracold atom held in a driven double well. In the high-frequency regime, we analytically obtain the quasienergies, the Floquet states, and the non-Floquet state of this system. When the system parameters are properly selected, the non-Floquet state reduces to special quantum states of simple forms which can provide a more intuitive understanding of some interesting quantum spin dynamical phenomena, such as the intrawell spin–flipping, the interwell spin-conserving tunneling, and the interwell spin–flipping tunneling. Specially, for the interwell spin–flipping tunneling, we surprisingly find that the selective coherent destruction of tunneling (SCDT) can occur at the anti-crossing (non-collapse) points of quasienergy spectrum, which breaks the conventional understanding that the SCDT is associated with the crossing of quasienergy levels. Further, we reveal the interwell spin–flipping tunneling strongly depends on the initial spin direction and the initial position of the SO-coupled atom. These novel results can be readily tested by the current experimental setups and may be useful for the design of spintronic devices.

Study on Rebounding Height of Capsule-shaped Object Based on Serial Coefficient of Restitution

The capsule-shaped object, when vertically released at certain initial angular velocity, can easily rebound to exceed the release height. The high-speed camera is used to record experimental images. The software, Tracker, is used to track experimental data. Finally, serial coefficient of restitution and spin parameter can be statistically summarized. MATLAB is used to process images to obtain the correlation between relevant data of the capsule rebounding status and serial coefficient of restitution, and bases for spin direction changes before and after rebounding of the capsule. ANSYS is employed to obtain simulation data. At last, evidence is provided to substantiate that the serial coefficient of restitution can, under some conditions, allow the capsule-shaped object can rebound higher than the release height, and that the spin direction and status of the capsule-shaped object can be identified by the value of spin parameter.