Effective Spin Research Articles

Thermal transport and spin–phonon interaction in magnetic Janus Cr2X3S3 (X = Br, I) monolayers

Comprehending the relationship between spin and phonons is essential to regulate the lattice thermal conductivity in 2D magnetic materials. Lattice thermal conductivity is a relevant part to consider in magnetic data storage and the working of spin-based devices. In this article, we examined the origin and effect of spin–phonon coupling (SPC) on the lattice thermal conductivity of pristine CrI3 monolayer-based Janus monolayers Cr2X3S3 (X=Br,I). We find a high SPC in these Janus monolayers due to in-plane Cr–S atomic vibrations. We observe a reduction in the lattice thermal conductivity at Janus monolayer magnetic states (∼52.3% in Cr2Br3S3 and ∼63.9% in Cr2I3S3) compared to its paramagnetic states. The analysis is also conducted to determine which magnetic state has more anharmonicity using potential energy wells. A wide range of 2D magnetic materials can benefit from our results in the future development of spin-based thermal devices.

Quark spin effects in e+e− annihilation: A Monte Carlo event generator study

Quark spin effects in e+e− annihilation to pseudoscalar and vector mesons are implemented for the first time in the Monte Carlo event generator. The spin-dependent fragmentation of the string stretched between the produced quark-antiquark pair with correlated spin states is described by the string+P30 model implemented in the string fragmentation routine of by using the package. The simulated events are used to study the model predictions for the Collins asymmetries of mesons produced back-to-back in the e+e− center of mass system by using both the thrust axis method and the hadronic plane method. The obtained asymmetries are compared to the available data from the BELLE and experiments and the underlying Collins analyzing power from the string+P30 model is compared with phenomenological extractions. Published by the American Physical Society 2024

Crystalline electric field excitations and their nonlinear splitting under magnetic fields in YbOCl

Recently reported van der Waals layered honeycomb rare-earth chalcohalides REChX (RE = rare earth, Ch = chalcogen, and X = halogen) are considered to be promising Kitaev spin liquid (KSL) candidates. The high-quality single crystals of YbOCl, a representative member of the family with an effective spin of 1/2, are available now. The crystalline electric field (CEF) excitations in a rare-earth spin system are fundamentally important for understanding both finite-temperature and ground-state magnetism but remain unexplored in YbOCl so far. In this paper, we conduct a comprehensive Raman scattering study to unambiguously identify the CEF excitations in YbOCl and determine the CEF parameters and wave functions. Our Raman experiments further reveal the anomalous nonlinear CEF splitting under magnetic fields. We have grown single crystals of YbOCl, the nonmagnetic LuOCl, and the diluted magnetic Lu0.86Yb0.14OCl to make a completely comparative investigation. Polarized Raman spectra on the samples at 1.8 K allow us to clearly assign all the Raman-active phonon modes and explicitly identify the CEF excitations in YbOCl. The CEF excitations are further examined using temperature-dependent Raman measurements and careful symmetry analysis based on Raman tensors related to CEF excitations. By applying the CEF Hamiltonian to the experimentally determined CEF excitations, we extract the CEF parameters and eventually determine the CEF wave functions. The study experimentally pins down the CEF excitations in the Kitaev compound YbOCl and sets a foundation for understanding its finite-temperature magnetism and exploring the possible nontrivial spin ground state. Published by the American Physical Society 2024

An upper limit on the spins of merging binary black holes formed through isolated binary evolution

As the sensitivity of ground-based gravitational wave detectors progressively increases, observations of black hole mergers will provide us with the joint distribution of their masses and spins. This will be a critical benchmark to validate different formation scenarios. Merging binary black holes formed through the evolution of isolated binary systems require both components to be stripped of their hydrogen envelopes before core-collapse. The rotation rates of such stripped stars are constrained by the critical rotation limit at their surface, including its deviation from the Keplerian value owing to the outward force provided by radiation. This sets a restriction on their angular momentum content at core-collapse. We aim to determine if this restriction plays a role in the spins of binary black hole mergers. We used detailed calculations of stripped stars with the MESA code at low metallicities ($Z=Z_ $Z_ and $Z_ to determine the dimensionless spins of black holes produced by critically rotating stellar progenitors. To study how such progenitors can arise, we considered their formation through chemically homogeneous evolution (CHE) in binary stars. We used a semi-analytical model to study the physical processes that determine the final angular momentum of CHE binaries, and compared our results against available population synthesis models that rely on detailed binary evolution calculations. We find that above black hole masses of $ 25M_ the dimensionless spin parameter of critically rotating stripped stars ($a=Jc/(GM^2)$) is below unity. This results in an exclusion region at high chirp masses and effective spins that cannot be populated by isolated binary evolution. CHE can produce binaries where both black holes hit this limit, producing a pileup at the boundary of the excluded region. High-spin black holes arise from very low-metallicity CHE systems with short delay times, which merge at higher redshifts. On the other hand, the contribution of CHE to merging binary black holes detected in the third observing run of the LVK collaboration is expected to be dominated by systems with low spins ($ eff <0.5$) that merge near redshift zero. Owing to its higher projected sensitivity and runtime, the fourth observing run of the LVK collaboration can potentially place constraints on the high-spin population and the existence of a limit set by critical rotation.

The Effect of Seeding Method on The Growth of Zinc Oxide Nanorods

The paper presents the investigation of the method of seeding process for the growth of zinc oxide (ZnO) nanorods (NRs) on the glass substrate as an electron transport layer (ETL) for solar cells. The ZnO NRs were grown by using the hydrothermal method. The seeding process was done via average deposition of zinc crystallite on the glass surface, and the process was compared between with and without spin coating technique. The effect of spin coating parameters during seeding phase on the growth of ZnO nanorods was also investigated in this study. It was found that the sample prepared using the unfiltered solution without spin coating in the seeding phase exhibited the densest ZnO NRs layer with the highest absorption coefficient and high crystallinity.

Dual Signature of Chirality Induced Spin Selectivity through Spontaneous Resolution of 2D Metal‐Organic Frameworks

The Chiral‐Induced Spin Selectivity (CISS) effect has emerged as a fascinating phenomenon within the realm of electron’s spin manipulation, showcasing a unique interplay between electron’s spin and molecular chirality. Subsequent to its discovery, researchers have been actively involved in exploring the new chiral molecules as effective spin filters. In the realm of observing the CISS effect, the conventional approach has mandated the utilization of two distinct enantiomers of chiral molecules. However, this present study represents a significant advancement by demonstrating the ability to control both spin states of electrons in a single system. In this work, we have demonstrated the preparation of chiral metal‐organic frameworks (MOFs) via a "spontaneous resolution" process, obviating the requirement for chiral sources. Remarkably, this work signifies the first instance of achieving dual signature of spin selectivity from a single and exclusively achiral system through a spontaneous resolution process. This holds immense potential as it facilitates the production of two distinct spin‐filtering materials from a unified system. In overall, the significant findings achieved using these robust and easily synthesized MOF crystals without the requirement for chiral medium represent a crucial advancement in enhancing the effectiveness of spin filtering materials to produce spintronic devices.

Dual Signature of Chirality Induced Spin Selectivity through Spontaneous Resolution of 2D Metal-Organic Frameworks.

The Chiral-Induced Spin Selectivity (CISS) effect has emerged as a fascinating phenomenon within the realm of electron's spin manipulation, showcasing a unique interplay between electron's spin and molecular chirality. Subsequent to its discovery, researchers have been actively involved in exploring the new chiral molecules as effective spin filters. In the realm of observing the CISS effect, the conventional approach has mandated the utilization of two distinct enantiomers of chiral molecules. However, this present study represents a significant advancement by demonstrating the ability to control both spin states of electrons in a single system. In this work, we have demonstrated the preparation of chiral metal-organic frameworks (MOFs) via a "spontaneous resolution" process, obviating the requirement for chiral sources. Remarkably, this work signifies the first instance of achieving dual signature of spin selectivity from a single and exclusively achiral system through a spontaneous resolution process. This holds immense potential as it facilitates the production of two distinct spin-filtering materials from a unified system. In overall, the significant findings achieved using these robust and easily synthesized MOF crystals without the requirement for chiral medium represent a crucial advancement in enhancing the effectiveness of spin filtering materials to produce spintronic devices.

Double-Q Checkerboard Bubble Crystal in Centrosymmetric Tetragonal Magnets

We report our numerical studies on the emergence of a double-Q checkerboard bubble crystal in centrosymmetric tetragonal magnets. The double-Q checkerboard bubble crystal is characterized by a fourfold-symmetric collinear spin configuration consisting of a superposition of two sinusoidal waves with the out-of-plane spin modulations along the [110] and [1¯10] directions. The numerical calculations based on the simulated annealing for an effective spin model with the momentum-resolved easy-axis exchange interactions reveal that the double-Q checkerboard bubble crystal is energetically degenerate with the single-Q collinear state when the ordering wave vector lies on the quarter of the reciprocal lattice vector along the ⟨110⟩ direction. We show that such a degeneracy is lifted by considering the biquadratic interaction. We also find that the double-Q checkerboard bubble crystal turns into another double-Q state characterized by the in-plane spin modulations by increasing an external magnetic field.

Spin Crossover and Its Application in Organometallic Catalysis: Concepts and Recent Progress.

Spin crossover is one of the most important properties of open-shell metal complexes. In organometallic catalytic reactions, catalysts can alter reaction kinetics by spin crossover, i.e., accelerating or hindering the reaction progression, as well as altering reaction pathways, modulating the reaction selectivity or promoting new reactions. This personal account outlines the introduction and development of important concepts such as "two-state reactivity" involving spin crossover, and proposes a new concept, "spin-responsive catalysis" to summarize the catalytic processes in which spin effects are present. Finally, the electronic mechanism of spin crossover accelerating the reaction and the role of spin crossover in changing the reaction path and regulating the reaction selectivity are introduced by taking two recent typical iron-catalyzed reactions recently reported by our group as examples.

Accretion mediated spin-eccentricity correlations in LISA massive black hole binaries

Abstract We examine expected effective spin (χeff, 1yr) and orbital eccentricity ($e_{1\rm yr}$) correlations for a population of observable equal-mass massive black hole binaries (MBHBs) with total redshifted mass Mz ∼ [104.5, 107.5] M⊙ embedded in a circumbinary disc (CBD) at redshifts z = 1 and z = 2, one-year before merging in the LISA band. We find a strong correlation between measurable eccentricity and negative effective spin for MBHBs that are carried to merger by retrograde accretion. This is due to the well-established eccentricity pumping of retrograde accretion and less-well-established formation of retrograde minidiscs coupled with a stable retrograde CBD throughout the binary evolution from the self-gravitating radius. Conversely, prograde accretion channels result in positive $\chi _{{\rm eff},1\rm yr}$ and non-measurable $e_{1\rm yr}$ except for almost unity Eddington ratio and Mz ≲ 105 M⊙ MBHBs at z = 1. This clear contrast between the two CBD orientations – and particularly the unique signature of retrograde configurations – provides a promising way to unlock the mysteries of MBHB formation channels in the LISA era.

Quantum radiation reaction: Analytical approximations and obtaining the spectrum from moments

We derive analytical χ≪1 approximations for spin-dependent quantum radiation reaction for locally constant and locally monochromatic fields. We show how to factor out fast spin oscillations and obtain the degree of polarization in the plane orthogonal to the magnetic field from the Frobenius norm of the Mueller matrix. We show that spin effects lead to a transseries in χ, with powers χk, logarithms (lnχ)k, and oscillating terms, cos(…/χ) and sin(…/χ). In our approach we can obtain each moment, ⟨(kP)m⟩, of the light-front longitudinal momentum independently of the other moments and without considering the spectrum. We show how to obtain a low-energy expansion of the spectrum from the moments by treating m as a continuous, complex parameter and performing an inverse Mellin transform. We also show how to obtain the spectrum, without making a low-energy approximation, from a handful of moments using the principle of maximum entropy. Published by the American Physical Society 2024

Anion Exchange and Lateral Heterostructure Formation in Ferromagnetic PEA2Cr(Cl,Br)4 Two-Dimensional Perovskites.

Postsynthetic vapor-phase anion exchange in the ferromagnetic two-dimensional (2D) hybrid metal-halide perovskite, PEA2CrCl4 (PEA+ = phenethylammonium), is reported. Anion exchange using vaporous trimethylsilyl bromide (TMS-Br) is shown to drive complete conversion of solution-processed PEA2CrCl4 polycrystalline thin films to PEA2CrBr4. Low-temperature magnetic circular dichroism spectroscopy indicates ferromagnetic ordering in these PEA2CrCl4 and PEA2CrBr4 films. Via partial anion exchange of exfoliated flakes of PEA2CrCl4 single crystals, we demonstrate that it is possible to generate abrupt lateral PEA2CrCl4/PEA2CrBr4 magneto-heterointerfaces. Kinetic studies reveal that lateral heterostructure formation is dictated by rapid edge-site halide exchange followed by slower intralayer bromide diffusion, and there is negligible interlayer (3D) bromide or TMS-Br diffusion. The importance of the bulky PEA+ interlayer cation in suppressing 3D diffusion is highlighted by parallel anion-exchange experiments on MA2CrCl4 (MA+ = methylammonium), which instead show 3D exchange. Comparison of anion-exchange reactions in PEA2CrCl4, PEA2MnCl4, and PEA2PbCl4 shows that 2D bromide diffusion is slowest in PEA2CrCl4, attributed to the antiferrodistortive ordering found in this composition. In addition to demonstrating both postsynthetic composition control and heterostructure formation in ferromagnetic Cr-based 2D perovskites for the first time, these results also advance our fundamental understanding of ion-exchange processes in this relatively unexplored family of 2D perovskites, broadening opportunities for investigation and control of novel spin effects in low-dimensional metal-halide perovskites.

Analysis of a brake squeal functional model using a linear parameter varying perspective

Brake squeal is a limit cycle vibration induced by mode coupling instability that depends on operating conditions such as applied pressure, temperature, and disc velocity. This work proposes a simplified functional model of brake squeal that reproduces the main characteristics observed in a full-scale industrial test campaign: vibration growth, limit cycle saturation, vibration decay and parametric dependence. The proposed functional model differs from the well-known Hoffmann model by the introduction of a nonlinear contact law and a quasi-static pressure loading. First, using a harmonic balance perspective, non-linear forces are shown to lead to a pressure and amplitude dependent contact stiffness. This Linear Parameter Varying perspective allows complex mode computations in the pressure/amplitude domain which are then correlated with a series of transient responses of the nonlinear modes for three different pressure profiles. The chosen profiles represent usual experiments: drag where a constant pressure is applied, pressure ramps and pressure oscillations mimicking the effect of wheel spin on the contact surfaces.

Kinetic theory of vacuum pair production in uniform electric fields revisited

We investigate the phenomenon of electron-positron pair production from vacuum in the presence of a uniform time-dependent electric field of arbitrary polarization. Taking into account the interaction with the external classical background in a nonperturbative manner, we quantize the electron-positron field and derive a system of ten quantum kinetic equations (QKEs) showing that the previously-used QKEs are incorrect once the external field rotates in space. We employ then the Wigner-function formalism of the field quantization and establish a direct connection between the Dirac-Heisenberg-Wigner (DHW) approach to investigating the vacuum pair-production process and the QKEs. We provide a self-contained description of the two theoretical frameworks rigorously proving their equivalence and present an exact one-to-one correspondence between the kinetic functions involved within the two techniques. Special focus is placed on the analysis of the spin effects in the final particle distributions. Published by the American Physical Society 2024

Effect of spin coating speeds on electrical and optical characteristic of perovskite SrTiO3 thin films prepared by sol-gel method

The perovskite strontium titanate (SrTiO3/STO) was prepared by the sol-gel process, and the STO thin film was deposited onto a glass substrate by the spin coating method. Effect of different spin coating speeds on the thickness, structural, optical, and electrical properties of the STO thin films was discussed. Five STO films with various spin coating parameters of 2000, 4000, 6000, 8000, and 10000 RPM were prepared. Thickness profilometer tests have shown that the thickness of the STO film changes from 802 nm at 10000 RPM to 1321 nm at 2000 RPM spin coating speed. The prepared STO films morphology was examined by scanning electron microscope. X-ray diffraction measurements have shown that crystalline STO films have been produced with a cubic perovskite structure. The optical properties of the prepared STO films were investigated using an ultraviolet visible spectrophotometer, and the results indicated that the STO film at 8000 and 4000 RPM spin speed show the lowest and the maximum optical band gap (2.83 and 2.90 eV, respectively). All STO films have absorption coefficient values higher than 103 cm−1. The prepared STO thin films had a refractive index between 2.40 and 2.42. The electrical characteristics of the prepared STO films were investigated using the four-point probe method, and it was found that as the spin coating speed increased from 2000 to 8000 RPM, the resistivity of the STO films reduced from 6.629∗1010 to 3.009∗1010 Ω. Moreover, the STO film at 8000 RPM spin speed has the best electrical conductivity (3.301∗10−5 S m−1).

Spin effect in the ferromagnetic organic photovoltaics cells

In organic photovoltaic devices, the separation and transport of photogenerated charges play crucial roles for power conversion efficiency. Magnetic doping in organic solar cells can effectively enhance the power conversion efficiency by introducing a static magnetic field. In this study, we observed that in pure organic magnetic solar cells, the spin-polarization-induced spin scattering effect can also efficiently modulate the photocurrent in solar cells. Compared to the demagnetized state, the short-circuit current of PTB7:nw-P3HT:PCBM solar cells increased by approximately 0.3% after magnetization. The dielectric constant only increased by about 0.05%. However, above the Curie temperature 310 K, the long-range spin order in PTB7:nw-P3HT:PCBM solar cells disappears, resulting in consistent circuit currents before and after magnetization. Therefore, magnetic doping can enhance the short-circuit current in organic solar cells by weakening the spin scattering effect and enhancing the charge carrier mobility.

Subwavelength quantum Hall spin effects in spatially elliptical coiled phononic crystals based on the local resonance principle

Subwavelength quantum Hall spin effects in spatially elliptical coiled phononic crystals based on the local resonance principle

Radiated Sound and Transmitted Vibration Following the Ball/Racket Impact of a Tennis Serve

Shock-induced vibrations transmitted from the racket to the tennis player’s upper limb have interested researchers, whether for investigating their effect on injury risk, or for designing new equipment. Measuring these vibrations is, however, very challenging in an ecological playing situation: sensors must be of very high quality in order to precisely measure high-energy and broad-frequency signals, as well as non-invasive in order to allow the players to perform their usual movements. The working hypothesis of this paper is that contactless sound recordings of the ball/racket impact carry the same information as direct vibratory measurements. The present study focuses on the tennis serve, as being tennis’ most energy-demanding stroke, therefore possibly being the most traumatic stroke for the upper limb. This article aims (a) to evaluate the propagation of vibration from the racket to the upper limb; and (b) to identify correlations with acoustic signals collected simultaneously. Eight expert tennis players performed serves with three rackets and two ball spin effects. Accelerometers measured the vibration on the racket and at five locations on the upper limb, and a microphone measured the impact sound. Resulting signals were analyzed in terms of energy and spectral descriptors. Results showed that flat serves produced louder sounds, higher vibration levels, lower acoustic spectral centroids, and higher vibratory spectral centroids than kick serves. The racket only had a marginal influence. Similarities between acoustic and vibratory measurements were found (levels were correlated), but so were differences (spectral centroids tended to be negatively correlated), encouraging further studies on the link between sound and vibration for the in situ measurement of shock-induced vibration.

Regulating Fe Intermediate Spin States via FeN4‐Cl‐Ti Structure for Enhanced Oxygen Reduction

AbstractModulating the spin states of FeN4 moieties is critical for enhancing the electrocatalytic oxygen reduction reaction (ORR). In this study, Ti4N3Clx and Ti4N3Ox MXenes are synthesized and functionalized with iron phthalocyanine (FePc) to form model catalysts with well‐defined FeN4‐Cl‐Ti and FeN4‐O‐Ti structures, respectively. The FeN4‐Cl‐Ti structure, formed within the Ti4N3Clx/FePc composite, enables precise modulation of FeN4 spin states from low to intermediate spin, significantly enhancing ORR performance. In contrast, the FeN4‐O‐Ti structure in Ti4N3Ox/FePc shows less effective spin state modulation, leading to comparatively lower ORR activity. Compared to FePc and Ti4N3Ox/FePc, Ti4N3Clx/FePc demonstrates superior electrochemical performance, with an ORR half‐wave potential of +0.91 V versus RHE and doubled power densities in Zn–air batteries (214.5 mW cm−2). Theoretical studies confirm that the intermediate spin states induced by the weak‐field ligand‐modified FeN4‐Cl‐Ti structure in Ti4N3Clx/FePc facilitate electron filling in the antibonding orbital composed of Fe 3dz2 and O2 π* orbitals, greatly enhancing O₂ activation and ORR activity. These findings underscore the superior catalytic properties of FeN4‐Cl‐Ti compared to FeN4‐O‐Ti, advancing the understanding of spin state‐related catalytic mechanisms and guiding the design of high‐performance ORR catalysts.

Effective spin models and magnetic phases of an insulating bosonic ladder with unconventional synthetic flux

We investigate the Mott insulating phases of a two-component bosonic lattice gas in the presence of gauge field. Such a system is described by a two-leg ladder model with an unconventional flux. The synthetic flux is generated by the spin-dependent tunneling and the site-dependent spin-flip. In the Mott regime, these two effects lead to Dzyaloshinskii-Moriya (DM) interaction and an external field that is rotating in the xy-plane. We obtain a very general XYZ model with the DM interaction, the spiral field, and the transverse field. Various interesting magnetic Hamiltonians can be covered by adjusting lattice parameters. The DM interaction or the spiral field can lead to spiral order when they appear alone. The interplay of DM coupling and spiral field leads to the emergence of a new multi-frequency spiral order between the paramagnetic phase and the spiral ferromagnetic phase. Ground state phases are investigated by focusing on order parameters, spin-spin correlation functions, and structure factors. Calculations are performed by using time evolution block decimation (TEBD) based on matrix product state (MPS).