Magnetic Momentum Research Articles

The fractional angular momentum realized by a neutral cold atom

Inspired by the electromagnetic duality, we propose an approach to realize the fractional angular momentum by using a cold atom which possesses a permanent magnetic dipole momentum. This atom interacts with two electric fields and is trapped by a harmonic potential which enable the motion of the atom to be planar and rotationally symmetric. We show that eigenvalues of the canonical angular momentum of the cold atom can take fractional values when the atom is cooled down to its lowest kinetic energy level. The fractional part of canonical angular momentum is dual to that of the fractional angular momenta realized by using a charged particle. Another approach of getting the fractional angular momentum is also presented. The differences between these two approaches are investigated.

Two photon physics at BESIII

The anomalous magnetic momentum of the muon, aµ = (g−2), has been considered as one of the variables with which to test the completeness of the Standard Model. It has been precisely measured experimentally and calculated theoretically, but there is a 3 to 4 standard deviations between measurement and calculation. The dominant contribution to the uncertainty in the theoretical calculation comes from the hadronic part, including hadronic vacuum polarization and hadronic light-by-light scattering. The two-photon fusion process at electron-positron colliders can be used to measure the space-like transition form factors, which will served as an input or constraint to the calculation of the hadronic light-by-light contribution to aµ. Studies of the form factors using two-photon processes for π0, η and η′, as well as the cross-section of γγ* → π+π− are presented.

Origin of the magnetic momentum for regular electrically charged objects described by nonlinear electrodynamics coupled to gravity

Dynamical equations of nonlinear electrodynamics minimally coupled to gravity (NED–GR), admit the class of regular solutions, asymptotically Kerr–Newman for a distant observer, which describe regular electrically charged rotating black holes and spinning electromagnetic solitons with the angular momentum [Formula: see text] and the gyromagnetic ratio [Formula: see text]. Their basic generic feature is the existence of the interior de Sitter equatorial disk of the radius [Formula: see text] with the equation-of-state [Formula: see text] in the co-rotating frame, with the properties of a perfect conductor and ideal diamagnetic, and with the superconducting ring current along the edge of the disk, which replaces the ring singularity of the Kerr–Newman geometry and provides the nondissipative source of electromagnetic fields and the origin of an intrinsic magnetic momentum for an electrically charged regular object described by NED–GR. Generic features of the electromagnetic soliton with the parameters of the electron, [Formula: see text], suggest that the intrinsic origin of the electron magnetic momentum can be a superconducting ring current evaluated as [Formula: see text] A.

Does Misalignment between Magnetic Field and Angular Momentum Enhance or Suppress Circumstellar Disk Formation?

Abstract The effect of misalignment between the magnetic field and the angular momentum of molecular cloud cores on the angular momentum evolution during the gravitational collapse is investigated by ideal and non-ideal MHD simulations. For the non-ideal effect, we consider the ohmic and ambipolar diffusion. Previous studies that considered the misalignment reported qualitatively contradicting results. Magnetic braking was reported as being either strengthened or weakened by misalignment in different studies. We conducted simulations of cloud core collapse by varying the stability parameter α (the ratio of the thermal to gravitational energy of the core) with and without including magnetic diffusion. The non-ideal MHD simulations show the central angular momentum of the core, with θ = 0° ( ) being always greater than that with θ = 90° ( ), independently of α, meaning that circumstellar disks form more easily in a core with θ = 0°. The ideal MHD simulations, in contrast, show the central angular momentum of the core with θ = 90° being greater than with θ = 0° for small α and smaller for large α. Inspection of the angular momentum evolution of the fluid elements reveals three mechanisms contributing to the evolution of the angular momentum: (i) magnetic braking in the isothermal collapse phase, (ii) selective accretion of the rapidly (for θ = 90°) or slowly (for θ = 0°) rotating fluid elements to the central region, and (iii) magnetic braking in the first core and the disk. The difference between the ideal and non-ideal simulations arises from the different efficiencies of (iii).

Strain effect of high Tc ferromagnetism in Mo-doped SnS2 monolayer

Endowing the nonmagnetic 2D materials with room temperature ferromagnetism (RTFM) is imperative for low-dimensional spintronic applications. Here, the electronic and magnetic properties of Mo-doped SnS2 monolayer are investigated using first-principles calculations. Numerical results show that the Mo dopant induces a magnetic momentum of 2μB, which can be attributed to the 2 spin-parallel Mo 4_d electrons that occupy the t2g orbitals split by D3d crystal field. Based on mean-field theory and Heisenberg model, Curie temperature (TC) is calculated to be 865.7 K. Applying biaxial strain, the doped system shows half-metallic characteristics in the range −10% to +4%. Beyond +4%, a transformation from half-metal to semiconductor occurs. Due to the symmetry-reserved crystal structure, the compound exhibits robust magnetic momentum of 2μB in the affordable biaxial strain range. Our calculations imply that Mo-doped SnS2 monolayer is a high TC strong ferromagnetism, and can be a promising candidate for new spintronic devices.

Magnonic noise and Wiedemann-Franz law

We theoretically establish mutual relations among magnetic momentum, heat, and fluctuations of propagating magnons in a ferromagnetic insulating junction in terms of noise and the bosonic Wiedemann-Franz (WF) law. Using the Schwinger-Keldysh formalism, we calculate all transport coefficients of a noise spectrum for both magnonic spin and heat currents, and establish Onsager relations between the thermomagnetic currents and the zero-frequency noise. Making use of the magnonic WF law and the Seebeck coefficient in the low-temperature limit, we theoretically discover universal relations, i.e. being independent of material parameters, for both the nonequilibrium and equilibrium noise, and show that each noise is described solely in terms of thermal conductance. Finally, we introduce a magnonic spin-analog of the Fano factor, noise-to-current ratio, and demonstrate that the magnonic spin-Fano factor reduces to a universal value in the low-temperature limit and it remains valid even beyond a linear response regime.

Is the half-integer spin a first level approximation of the golden mean hierarchy?

Abstract This paper shows that the half-integer spin is the first level of the quantized golden mean, and the electron magnetic momentum can be exactly calculated using the classic quantum mechanics without the spin-1/2 theory, where the g-factor was introduced to predict the magnetic momentum. The golden mean predicts an exact value of 2 for the g-factor, and other quantized numbers of the golden mean lead the g-factor to deviation from 2. Our results demonstrate that quantized golden mean evokes a new and challenging branch of physics. We anticipate the quantized golden mean to be a starting point to solve puzzle and paradox in physics and to revitalize a more sophisticated physics based on the golden mean.

Self-consistent description of the tangential-discontinuity-type current sheet, using the particle trajectory method and angular variables

The description of the dynamics of charged-particles in an inhomogeneous magnetic field is a fundamental problem in space plasma physics. Since, this dynamics has a character of a nonlinear oscillator, the traditionally used approaches involve certain limiting conditions regarding the scales of magnetic field, particle motion, and the assumptions about conservation of specific invariants (e.g., the magnetic momentum, integrals of action, etc.). Such approaches naturally restrict the detailization the considered particle dynamics which is described in terms of the integral characteristics and averaged parameters of motion. However, in some regions the precise account of the particle trajectory details and the motion features (e.g., the phase of gyration) are of crucial importance. In this paper, we present a method for the description of particle dynamics, based on a new system of differential equations for the particle pitch-angle θ and phase of rotation ϕ, which are derived from the analysis of the particle trajectory in a given magnetic field. It enables an easy and comprehensive description of a number of elementary problems, which form the basis for more complex natural cases in space physics. The developed method admits generalization to the case of the particle ensemble, which makes it possible to find a set of the self-consistent solutions for tangential current sheets within the frame of the kinetic approach.

Scale separated low viscosity dynamos and dissipation within the Earth\u2019s core

The mechanism by which the Earth’s magnetic field is generated is thought to be thermal convection in the metallic liquid iron core. Here we present results of a suite of self-consistent spherical shell computations with ultra-low viscosities that replicate this mechanism, but using diffusivities of momentum and magnetic field that are notably dissimilar from one another. This leads to significant scale separation between magnetic and velocity fields, the latter being dominated by small scales. We show a zeroth order balance between the azimuthally-averaged parts of the Coriolis and Lorentz forces at large scales, which occurs when the diffusivities of magnetic field and momentum differ so much, as in our model. Outside boundary layers, viscous forces have a magnitude that is about one thousandth of the Lorentz force. In this dynamo dissipation is almost exclusively Ohmic, as in the Earth, with convection inside the so-called tangent cylinder playing a crucial role; it is also in the “strong field” regime, with significantly more magnetic energy than kinetic energy (as in the Earth). We finally show a robust empirical scaling law between magnetic dissipation and magnetic energy.

The impact of non-ideal effects on the circumstellar disk evolution and their observational signatures

AbstractIt has been recognized that non-ideal MHD effects (Ohmic diffusion, Hall effect, ambipolar diffusion) play crucial roles for the circumstellar disk formation and evolution. Ohmic and ambipolar diffusion decouple the gas and the magnetic field, and significantly reduces the magnetic torque in the disk, which enables the formation of the circumstellar disk (e.g., Tsukamoto et al. 2015b). They set an upper limit to the magnetic field strength of ∼ 0.1 G around the disk (Masson et al. 2016). The Hall effect notably changes the magnetic torques in the envelope around the disk, and strengthens or weakens the magnetic braking depending on the relative orientation of magnetic field and angular momentum. This suggests that the bimodal evolution of the disk size possibly occurs in the early disk evolutionary phase (Tsukamoto et al. 2015a, Tsukamoto et al. 2017). Hall effect and ambipolar diffusion imprint the possibly observable characteristic velocity structures in the envelope of Class 0/I YSOs. Hall effect forms a counter-rotating envelope around the disk. Our simulations show that counter rotating envelope has the size of 100–1000 au and a recent observation actually infers such a structure (Takakuwaet al. 2018). Ambipolar diffusion causes the significant ion-neutral drift in the envelopes. Our simulations show that the drift velocity of ion could become 100-1000 ms–1.

Maximization of terahertz slow light by tuning the spoof localized surface plasmon induced transparency

This work numerically investigates a localized terahertz (THz) slow light phenomenon by tuning the spoof localized surface plasmon-induced transparency (PIT). A binary meta-molecule supports the interaction of the spoof localized surface plasmon (spoof-LSP), which is composed of a metallic arc and a textured circular cavity of periodic grooves. By tuning the central angle θ of the arc from 90 degrees to 170 degrees, a slow light plateau is found in the transparency window at certain frequency range. A maximum of 46 ps group delay is achieved at the θ of 135. The numerical mapping of the electromagnetic field indicates a new-born dipolar spoof-LSP that appears at the transparency windows on the circular cavity with opposite polarity to the spoof-LSP on the metallic arc. These two spoof-LSPs of opposite direction lead to a fake quadrupole, which will repel each other in magnetic dipole momentum. The slow light achieves maximum with the induced spoof-LSP and is the same as the origin spoof-LSP on the metallic arc in oscillation strength. This work paves a new way for the maximization of THz slow light.

Correlation between compensation temperatures of magnetization and angular momentum in GdFeCo ferrimagnets

Determining the angular momentum compensation temperature of ferrimagnets is an important step towards ferrimagnetic spintronics, but is not generally easy to achieve it experimentally. We propose a way to estimate the angular momentum compensation temperature of ferrimagnets. We find a linear relation between the compensation temperatures of the magnetization and angular momentum in GdFeCo ferrimagnetic materials, which is proved by theoretically as well as experimentally. The linearity comes from the power-law criticality and is governed by the Curie temperature and the Land\'e g factors of the elements composing the ferrimagnets. Therefore, measuring the magnetization compensation temperature and the Curie temperature, which are easily assessable experimentally, enables to estimate the angular momentum compensation temperature of ferrimagnets. Our study provides efficient avenues into an exciting world of ferrimagnetic spintronics.

Contribution of Iron Clusters to the Magnetic Properties of Pb1 – yFe y Te Alloys

The field dependences of the magnetization (temperatures T = 2.0–70 K, magnetic fields B ≤ 7.5 T) of the samples from a single-crystalline Pb1 – yFe y Te ingot (y = 0.02) grown by the Bridgman method are studied. It is established that the sample magnetization contains several major contributions such as the paramagnetism of iron ions, diamagnetism of the crystal lattice, and the contributions of charge carriers and clusters of iron atoms. The field dependences of the paramagnetic contribution of iron ions and the contribution of clusters of iron atoms are approximated by theoretical dependences based on the Brillouin and Langevin functions, respectively. The average concentrations and magnetic moment of clusters as well as the total magnetic momentum of clusters in the volume unit in the samples upon increasing the impurity concentration along the ingot are determined.

Theoretical proposal for determining angular momentum compensation in ferrimagnets

This work demonstrates that the magnetization and angular momentum compensation temperature (TMC and TAMC) in ferrimagnets (FiM) can be unambiguously determined by performing two sets of temperature dependent current switching, with the symmetry reverses at TMC and TAMC, respectively. A theoretical model based on the modified Landau-Lifshitz-Bloch equation is developed to systematically study the spin torque effect under different temperatures, and numerical simulations are performed to corroborate our proposal. Furthermore, we demonstrate that the recently reported linear relation between TAMC and TMC can be explained using the Curie-Weiss theory.

Scalar pair production in a magnetic field in de Sitter universe

The production of scalar particles by the dipole magnetic field in de Sitter expanding universe is analyzed. The amplitude and probability of transition are computed using perturbative methods. A graphical study of the transition probability is performed obtaining that the rate of pair production is important in the early universe. Our results prove that in the process of pair production by the external magnetic field the momentum conservation law is broken. We also found that the probabilities are maximum when the particles are emitted perpendicular to the direction of magnetic dipole momentum. The total probability is computed and is analysed in terms of the angle between particles momenta.

Galactic Disk Winds Driven by Cosmic Ray Pressure

Abstract Cosmic ray pressure gradients transfer energy and momentum to extraplanar gas in disk galaxies, potentially driving significant mass loss as galactic winds. This may be particularly important for launching high-velocity outflows of “cool” (T ≲ 104 K) gas. We study cosmic ray-driven disk winds using a simplified semi-analytic model assuming streamlines follow the large-scale gravitational potential gradient. We consider scaled Milky Way–like potentials including a disk, bulge, and halo with a range of halo velocities V H = 50–300 and streamline footpoints with radii in the disk R 0 = 1–16 kpc at a height of 1 kpc. Our solutions cover a wide range of footpoint gas velocity u 0, magnetic–to–cosmic ray pressure ratio, gas–to–cosmic ray pressure ratio, and angular momentum. Cosmic ray streaming at the Alfvén speed enables the effective sound speed C eff to increase from the footpoint to a critical point where C eff,c = u c ∼ V H; this differs from thermal winds, in which C eff decreases outward. The critical point is typically at a height of 1–6 kpc from the disk, increasing with V H, and the asymptotic wind velocity exceeds the escape speed of the halo. Mass-loss rates are insensitive to the footpoint values of the magnetic field and angular momentum. In addition to numerical parameter space exploration, we develop and compare to analytic scaling relations. We show that winds have mass-loss rates per unit area up to , where Π0 is the footpoint cosmic ray pressure and u 0 is set by the upwelling of galactic fountains. The predicted wind mass-loss rate exceeds the star formation rate for V H ≲ 200 and u 0 = 50 , a typical fountain velocity.

Copper Nanospheres Self‐Propelled into Continuums of Iron Nanoclusters to Fabricate and Engineer Two‐Dimensional Heterometallic Arrays under an External Magnetic Field

AbstractControlled dislocation/arrangement metals in a metallic network with nonmagnetic species presents a challenge to fabricate/engineer structured heterometallic compounds. Heterometallic structures have dangling bonds at the shell of neighboring metallic particles, and therefore present a strong strain field in the vicinity of these particles. These structures can be used as a suitable bed with high surface energy to catalyze organic reactions. Here, we show a method for the production of two‐dimensional (2‐D) arrays of Cu nanospheres self‐propelled into continuums of Fe nanoclusters. The synthesis was carried out under magnetic‐field induction (MFI) with adjusting intensity. Electromagnetic (EM) results show that Cu species trapping themselves at the Fe species interface under the influence of magnetic momentum of Fe particles and MFI to rearrange periodic particle arrays of Cu and Fe. The metallic regions in 2‐D composites appear to be efficient catalytic centers in Csp−S cross‐coupling reactions. The synergistic effect of metallic species is a key support for the high activity of 2‐D Cu/Fe nanocompounds in coupling reactions. Nanocompounds are very stable after multiple reaction cycles.

Structural, Elastic, Thermodynamic, Electronic, and Magnetic Investigations of Full-Heusler Compound Ag2CeAl: FP-LAPW Method

Structural, elastic, thermodynamic, electronic, and magnetic properties of the full-Heusler compound Ag2CeAl were determined using generalized gradient approximation with exchange-correlation functional GGA (PBEsol) with spin-orbit coupling (SOC) correction. The elastic modulus and their pressure dependence are calculated. From the elastic parameter behavior, it is inferred that this compound is elastically stable and ductile in nature. Through the quasi-harmonic Debye model, in which the phononic effect is considered the effect of pressure P (0 to 50) and temperature T (0 to 1000) on the lattice constant, the elastic parameters, bulk modulus B, heat capacity and thermal expansion α, internal energy U, entropy S, Debye temperature 𝜃D, Helmholtz free energy A, and Gibbs free energy G are investigated. The thermodynamic properties show that the compound Ag2CeAl is a heavy fermion material. The density of state (DOS), magnetic momentum, and band structure are computed, to investigate the magnetic and metallic characteristics. The calculated polarization of the compound is 77.34%. The obtained results are the first predictions of the physical properties for the rare-earth-based (Ce) full-Heusler Ag2CeAl.

Spin and momentum of the light fields in inhomogeneous dispersive media with application to surface plasmon-polariton waves

Following to the recently published approach [Phys. Rev. Lett. 119, 073901 (2017); New J. Phys., 123014 (2017)], we refine and accomplish the general scheme for the unified description of the momentum and angular momentum in complex media. The equations for the canonical (orbital) and spin linear momenta, orbital and spin angular momenta in a lossless inhomogeneous dispersive medium are presented in the compact form analogous to the Brillouin's relation for the energy. The results are applied to the surface plasmon-polariton (SPP) field, and the microscopic calculations support the phenomenological expectations. The refined general scheme correctly describes the unusual SPP properties (transverse spin, magnetization momentum) and additionally predicts the singular momentum contribution sharply localized at the metal-dielectric interface, which is confirmed by the microscopic analysis. The results can be useful in optical systems employing the structured light, especially for microoptics, plasmophotonics, optical sorting and micromanipulation.

Space-like transition form factors from BESIII

The anomalous magnetic momentum of muon, aμ, has been measured in experiment and calculated in theory with a precision up to ∼0.5 ppm. But there is a long standing 3 to 4 standard deviations between these two accurate values. The dominant contribution to the uncertainty in the theoretical calculation comes from the hadroninc contribution, including contributions from the hadronic vacuum polarization and the hadronic light-by-light. The meson transition form factors measured in two photon process at BESIII can be used as input or constrain for the calculation of the hadronic light-by-light contribution to aμ. Recent experimental activities, including the measurements of the transition form factor of π0, η, and η′, and the cross section of γγ⁎→π+π− are presented.