Different effects of Ce-doping on orbital and spin ordering in perovskite vanadate Sm_(1-χ)Ce_χ VO_3

The effects of Ce-doping on the phase transition of the orbital/spin ordering （OO/SO） are studied through the structural, magnetic, and electrical transport measurements of perovskite vanadate Sm1 x Ce x VO 3 . The measurements of structure show that the cell volume decreases as x≤ 0.05, and then increases as Ce-doping level increases further. The OO state exists but is suppressed progressively in the sample with x≤0.2 and disappears as x0.2. The temperature at which the C-type SO transition is present increases monotonically with Ce-doping level increasing. The temperature dependence of resistivity for each of the samples shows a semiconducting transport behavior and the transport can be well described by the thermal activation model. The activation energy first decreases as x ≤0.2, and then increases for further doping. The obtained results are discussed in terms of the mixed-valent state of the doped-Ce ions.

Spin, charge, and orbital orderings in iron-based superconductors

In this article, we briefly review spin, charge, and orbital orderings in iron-based superconductors, as well as the multi-orbital models. The interplay of spin, charge, and orbital orderings is a key to understand the high temperature superconductivity. As an illustration, we use the two-orbital model to show the spin and charge orderings in iron-based superconductors based on the mean-field approximation in real space. The typical spin and charge orderings are shown by choosing appropriate parameters, which are in good agreement with experiments. We also show the effect of Fe vacancies, which can introduce the nematic phase and interesting magnetic ground states. The orbital ordering is also discussed in iron-based superconductors. It is found that disorder may play a role to produce the superconductivity.

Ab initio nonadiabatic molecular dynamics study on spin–orbit coupling induced spin dynamics in ferromagnetic metals

Understanding the photoexcitation induced spin dynamics in ferromagnetic metals is important for the design of photo-controlled ultrafast spintronic device.In this work,by the ab initio nonadiabatic molecular dynamics simulation,we have studied the spin dynamics induced by spin–orbit coupling(SOC)in Co and Fe using both spin-diabatic and spin-adiabatic representations.In Co system,it is found that the Fermi surface(E_(F))is predominantly contributed by the spin-minority states.The SOC induced spin flip will occur for the photo-excited spin-majority electrons as they relax to the E_(F),and the spin-minority electrons tend to relax to the EFwith the same spin through the electron–phonon coupling(EPC).The reduction of spin-majority electrons and the increase of spin-minority electrons lead to demagnetization of Co within100 fs.By contrast,in Fe system,the E_(F) is dominated by the spin-majority states.In this case,the SOC induced spin flip occurs for the photo-excited spin-minority electrons,which leads to a magnetization enhancement.If we move the E_(F) of Fe to higher energy by 0.6eV,the E_(F) will be contributed by the spin-minority states and the demagnetization will be observed again.This work provides a new perspective for understanding the SOC induced spin dynamics mechanism in magnetic metal systems.

Effects of anharmonic lattice distortion on orbital and magnetic orderings in KCuF_3

Lattice, magnetic and orbital structures in KCuF3 are self-consistently determined by our cluster self-consistent field approach based on a spin-orbital-lattice Hamiltonian. Two stable structures are obtained and found to be degenerate, which confirms the presence of the coexistent phases observed experimentally. We clearly show that due to the inherent frustration, the ground state of the system only with the superexchange interaction is degenerate; while the Jahn-Teller distortion, especially the anharmonic effect, stabilizes the orbital ordered phase at about 23% in the x2-y2 orbit and at 77% in the 3z2-r2 orbit. Meanwhile the magnetic moment of Cu is considerably reduced to 0.56μB, and magnetic coupling strengths are highly anisotropic, Jx/Jxy ≈ 18. These results are in good agreement with the experiments, implying that the anharmonic Jahn-Teller effect plays an essential role in stabilising the orbital ordered ground state of KCuF3.

First-principles study of orbital ordering in cubic fluoride KCrF_3

Comprehensive first-principles calculations are performed to provide insight into the intriguing physical properties of the ternary cubic fluoride KCrF3. The electronic structures exhibit a prominent dependence on the effective local Coulomb interaction parameter Ueff. The ground state of the cubic phase is a ferromagnetic （FM） half-metal with Ueff equal to 0, 2, and 4 eV, whereas the insulating A-type antiferromagnetic （A-AFM） state with concomitant homogeneous orbital ordering is more robust than the FM state for Ueff exceeding 4 eV. We propose that the origin of the orbital ordering is purely electronic when the cooperative Jahn-Teller distortions are absent in cubic KCrF3.

Orbital Ordering Induced by Direct Coulomb Repulsion

我们与例如轨道的自由考虑 3d 电子的共价人物并且在这篇文章基于直接库仑排斥提出轨道的订的新机制(OO ) 。在在 180 度配置的邻近的离子之间的轨道轨道的相互作用(OO-I ) 被超交换精力统治的结果表演伴随了由一弱轨道纺纱的联合，并且在 90 度配置的 OO-I 被氧监视所在地的库仑排斥。ferro-OO 是为在 90 度配置的情况中的一个维的链的稳定的地面状态。

Tuning charge and orbital ordering in DyNiO_(3) by biaxial strain

The first-principles calculations were used to explore the tunable electronic structure in DyNiO_(3)(DNO)under the effects of the biaxial compressive and tensile strains.We explored how the biaxial strain tunes the orbital hybridization and influences the charge and orbital ordering states.We found that breathing mode and Jahn–Teller distortion play a primary role in charge ordering state and orbital ordering state,respectively.Additionally,the calculated results revealed that the biaxial strain has the ability to manipulate the phase competition between the two states.A phase transition point has been found under tensile train.If the biaxial train is larger than the point,the system favors orbital ordering state.If the strain is smaller than the point,the system is in charge ordering state favorably.

Asymmetrical spiral spectra and orbital angular momentum density of non-uniformly polarized vortex beams in uniaxial crystals

To explore the effect of non-uniform polarization on orbital angular momentum(OAM) in anisotropic medium, in this work investigated are the evolution of the spiral spectra and OAM densities of non-uniformly polarized vortex(NUPV)beams in uniaxial crystals propagating orthogonal to the optical axis, and also the case of uniformly polarized vortex(UPV)beams with left-handed elliptical polarization. In the input plane, the NUPV beams present their spiral spectra of m-mode concentrated at m = l ± 1 modes rather than m = l mode, and reveal the relation among topological charge l, mode of spiral spectra m and the power weight value Rmexpressed by l=∑^(∞)_(m)=-∞Rm. is still satisfied for UPV beams in uniaxially anisotropic crystals, whereas for NUPV beams their relations are no longer valid owing to non-uniform polarization. Furthermore, the analysis indicates that the asymmetrical distribution of power weight of spiral spectra and the non-zero value in the sum of longitudinal OAM densities originate from the initial non-uniform polarization and anisotropy in uniaxial crystals rather than topological charges. In addition, the relation between spiral spectrum and longitudinal OAM density is numerically discussed. This work may provide an avenue for OAM-based communications,optical metrology, and imaging by varying the initial non-uniform polarization.

Electrical manipulation of a hole‘spin'–orbit qubit in nanowire quantum dot:The nontrivial magnetic field effects

Strong‘spin’–orbit coupled one-dimensional hole gas is achievable in a Ge nanowire in the presence of a strong magnetic field.The strong magnetic field lifts the two-fold degeneracy in the hole subband dispersions,so that the effective low-energy subband dispersion exhibits strong spin–orbit coupling.Here,we study the electrical spin manipulation in a Ge nanowire quantum dot for both the lowest and second lowest hole subband dispersions.Using a finite square well to model the quantum dot confining potential,we calculate exactly the level splitting of the spin–orbit qubit and the Rabi frequency in the electric-dipole spin resonance.The spin–orbit coupling modulated longitudinal g-factor gso is not only non-vanishing but also magnetic field dependent.Moreover,the spin–orbit couplings of the lowest and second lowest subband dispersions have opposite magnetic dependences,so that the results for these two subband dispersions are totally different.It should be noticed that we focus only on the properties of the hole‘spin’instead of the real hole spin.

Rashba spin-orbit coupling induced rectified currents in monolayer graphene with exchange field and sublattice potential

We investigate the effect of Rashba spin-orbit coupling(RSOC)on photoconductivities of rectified currents in monolayer graphene with exchange field and sublattice potential.The system shows that the photoconductivities of resonant shift and injection current contributions are nonzero,while the photoconductivities of non-resonant shift current contribution are zero.We find that the RSOC induces a warping term,which leads to the nonzero rectified currents.Moreover,the photoconductivities of resonant injection(shift)current contribution are(not)related to the relaxation rate.The similar behavior can be found in other Dirac materials,and our findings provide a way to tune the nonlinear transport properties of Dirac materials.

Spin–orbit torque in perpendicularly magnetized[Pt/Ni]multilayers

The performance of spin–orbit torque(SOT)in heavy metal/ferromagnetic metal periodic multilayers has attracted widespread attention.In this paper,we have successfully fabricated a series of perpendicular magnetized[Pt(2-t)/Ni(t)]_4 multilayers,and studied the SOT in the multilayers by varying the thickness of Ni layer t.The current induced magnetization switching was achieved with a critical current density of 1×10^(7)A/cm^(2).The damping-like SOT efficiencyξ_(DL)was extracted from an extended harmonic Hall measurement.We demonstrated that theξ_(DL)can be effectively modulated by t_(Pt)/t_(Ni)ratio of Pt and Ni in the multilayers.The SOT investigation about the[Pt/Ni]N multilayers might provide new material candidates for practical perpendicular SOT-MRAM devices.

Orbital torque of Cr-induced magnetization switching in perpendicularly magnetized Pt/Co/Pt/Cr heterostructures

The spin–orbit torque via the spin Hall effect of heavy metals has shown promising prospect in driving the magnetization switching in spintronic devices due to the generated spin current from heavy metals.Recently,the 3d-light metals have been predicted the ability to generate orbital current and the associated orbital torques from the orbital Hall effect.However,few experiments have been carried out since it is quite hard to directly detect the orbital current-generated orbital torque.Here,we report an effective method to demonstrate the strong orbital torques in light metal Cr through a conversion process from orbital current to spin current by introducing the Pt interfacial layer in perpendicularly magnetized symmetric Pt/Co/Pt structures.A quite large and monotonically growth of orbital torque efficiency in Pt/Co/Pt/Cr with the increase of the thickness of Cr layer is obtained with the largest effective orbital torque efficiency around 2.6 Oe/(MA·cm^(-2))(1 Oe=79.5775 A·m^(-1)).The ability of orbital torque to drive the magnetization switching is also reported with the critical switching current density down to the order of 106A·cm^(-2).Our findings prove the efficiency for switching the magnetization from light metal Cr layers through the orbital Hall effect.

Optical spin-to-orbital angular momentum conversion in structured optical fields

We investigate the dynamic quantities:momentum,spin and orbital angular momenta(SAM and OAM),and their conversion relationship in the structured optical fields at subwavelength scales,where the spin–orbit interaction(SOI)plays a key role and determines the behaviors of light.Specifically,we examine a nanostructure of a Ag nanoparticle(Ag NP)attached on a cylindrical Ag nanowire(Ag NW)under illumination of elliptically polarized light.These dynamic quantities obey the Noether theorem,i.e.,for the Ag nanoparticle with spherical symmetry,the total angular momentum consisting of SAM and OAM conserves;for the Ag NW with translational symmetry,the orbital momentum conserves.Meanwhile,the spin-to-orbital angular momentum conversion is mediated by SOI arising from the spatial variation of the optical potential.In this nanostructure,the conservation of momentum imposes a strict restriction on the propagation direction of the surface plasmon polaritons along the Ag NW.Meanwhile,the orbital momentum is determined by the polarized properties of the excitation light and the topography of the Ag NP.Our work offers insights to comprehend the light behaviors in the structured optical fields in terms of the dynamic quantities and benefits to the design of optical nano-devices based on interactions between spin and orbital degrees of freedom.

Spin logic devices based on negative differential resistance -enhanced anomalous Hall effect

Owing to rapid developments in spintronics,spin-based logic devices have emerged as promising tools for next-generation computing technologies.This paper provides a comprehensive review of recent advancements in spin logic devices,particularly focusing on fundamental device concepts rooted in nanomagnets,magnetoresistive random access memory,spin–orbit torques,electric-field modu-lation,and magnetic domain walls.The operation principles of these devices are comprehensively analyzed,and recent progress in spin logic devices based on negative differential resistance-enhanced anomalous Hall effect is summarized.These devices exhibit reconfigur-able logic capabilities and integrate nonvolatile data storage and computing functionalities.For current-driven spin logic devices,negative differential resistance elements are employed to nonlinearly enhance anomalous Hall effect signals from magnetic bits,enabling reconfig-urable Boolean logic operations.Besides,voltage-driven spin logic devices employ another type of negative differential resistance ele-ment to achieve logic functionalities with excellent cascading ability.By cascading several elementary logic gates,the logic circuit of a full adder can be obtained,and the potential of voltage-driven spin logic devices for implementing complex logic functions can be veri-fied.This review contributes to the understanding of the evolving landscape of spin logic devices and underscores the promising pro-spects they offer for the future of emerging computing schemes.

On the Ground State of Spin Systems with Orbital Degeneracy

In order to understand the properties of the spin system with orbital degeneracy, we first study the ground state of the SU(4) spin-orbital model on a square lattice. The mean-field results suggest that for a small Hund's interaction, the flavor liquid state is stable against the solid state, but with sufficient deviation from the SU(4) limit the long-range order may be attained in 2D system. Fhrthermore, we employ a variational approach to calculate the phase diagram of the ground state and the temperature-dependent susceptibility by taking into account the Hund's interaction and the anisotropy in orbital wavefunctions. Finally, the implications for the experimental observations on the material,LiNiO2, are discussed.

Classical Ground State Spin Ordering of the Antiferromagnetic J_1-J_2 Model

The classical frustrated antiferromagnetic J_1–J_2 model is considered in a description of the classical spin wave for a vector spin system. Its ground state(GS) spin ordering is analyzed by minimizing its energy. Our analytical derivations show that all the spins in the GS phase must lie in planes that are parallel to each other. When applying the derived formulations to concrete lattices such as the square and simple cubic lattices, we find that in the large J_2 region, a large continuous GS degeneracy concluded by a qualitative analysis is lifted, and collinear striped ordering is selected as the GS phase.

Anderson localization of a spin–orbit coupled Bose–Einstein condensate in disorder potential

We present numerical results of a one-dimensional spin–orbit coupled Bose–Einstein condensate expanding in a speckle disorder potential by employing the Gross–Pitaevskii equation.Localization properties of a spin–orbit coupled Bose–Einstein condensate in zero-momentum phase,magnetic phase and stripe phase are studied.It is found that the localizing behavior in the zero-momentum phase is similar to the normal Bose–Einstein condensate.Moreover,in both magnetic phase and stripe phase,the localization length changes non-monotonically as the fitting interval increases.In magnetic phases,the Bose–Einstein condensate will experience spin relaxation in disorder potential.

Spin and Orbital Magnetisms of NiFe Compound:Density Functional Theory Study and Monte Carlo Simulation

The self-consistent ab initio calculations based on the density functional theory approach using the full potential linear augmented plane wave method are performed to investigate both the electronic and magnetic properties of the NiFe compound. Polarized spin within the framework of the ferromagnetic state between magnetic ions is considered. Also, magnetic moments considered to lie along （001） axes are computed. The Monte Carlo simulation is used to study the magnetic properties of NiFe. The transition temperature To, hysteresis loop, coercive field and remanent magnetization of the NiFe compound are obtained using the Monte Carlo simulation.

Orbital Spin: A New Hypothesis to Explain Precession of Equinox—The Third Motion of Earth

In this paper, the phenomena of Earth’s motion about its own axis, the ecliptic plane of the Earth’s orbit around the Sun, the definitions of equinoxes, the precession of equinoxes, Earth’s wobble and other astronomical terminology are briefly described. Some of the existing theories explaining the precession of equinox and their inadequacies are brought out. New Hypothesis is that precession of equinoxes is a direct result of Orbital spin of Earth in a retrograde direction—a celestial phenomenon similar to that of Moon’s Orbital spin around the Earth. The study of Moon’s orbit round the Earth reveals the exact movement of Earth’s orbit, which causes precession of equinoxes without any ambiguity. The analogy presented herein demonstrates the plausible hypothesis.

Controllable Spin Polarization of Charge Current by Rashba Spin Orbital Coupling

We report a theoretic study on modulating the spin polarization of charge current in a mesoscopic four-terminaldevice of cross structure by using the inverse spin hall effect.The scattering region of device is a two-dimensionalelectron gas(2DEG)with Rashba spin orbital interaction(RSOI),one of lead is ferromagnetic metal and other threeleads are spin-degenerate normal metals.By using Landauer-Büttiker formalism,we found that when a longitudinalcharge current Rows through 2DEG scattering region from FM lead by external bias,the transverse current can be eithera pure spin current or full-polarized charge current due to the combined effect of spin hall effect and its inverse process,and the polarization of this transverse current can be easily controlled by several device parameters such as the Fermienergy,ferromagnetic magnetization,and the RSOI constant.Our method may pave a new way to control the spinpolarization of a charge current.