Magnetic Momentum Research Articles

Ultrafast Dynamics of Domain Walls in Antiferromagnets and Ferrimagnets with Temperatures of Compensation of the Magnetic Moment and Angular Momentum (Brief Review)

Ultrafast Dynamics of Domain Walls in Antiferromagnets and Ferrimagnets with Temperatures of Compensation of the Magnetic Moment and Angular Momentum (Brief Review)

Energy spectra of graphene quantum dots induced between Landau levels

When an energy gap is induced in monolayer graphene the valley degeneracy is broken and the energy spectrum of a confined system such as a quantum dot, becomes rather complex exhibiting many irregular level crossings and small energy spacings, which are very sensitive to the applied magnetic field. Here we study the energy spectrum of a graphene quantum dot that is formed between Landau levels, and show that for the appropriate potential well the dot energy spectrum in the first Landau gap can have a simple pattern with energies coming from one of the two valleys only. This part of the spectrum has no crossings, has specific angular momentum numbers, and the energy spacing can be large enough, consequently, it can be probed with standard spectroscopic techniques. The magnetic field dependence of the dot levels as well as the effect of the mass-induced energy gap are examined, and some regimes leading to a controllable quantum dot are specified. At high magnetic fields and negative angular momentum a simple approximate method to the Dirac equation is developed, which gives further insight into the physics. The approximate energies exhibit the correct trends and agree well with the exact energies.

High‐Pressure Growth and Magnetic and Electrical Properties of EuB6 Nanowires

Using an iodine‐assisted autoclave technique, europium hexaboride (EuB6) nanowires are successfully prepared. The X‐ray diffraction (XRD) pattern confirms that the obtained black powders are pure‐phase EuB6 crystals. High‐resolution transmission electron microscopy (HRTEM) and selected‐area electron diffraction (SAED) images prove that the EuB6 nanowires are single crystals grown along the [001] direction. From the temperature‐dependent magnetic susceptibility results, EuB6 shows strong susceptibility at low temperature under 15 K, possessing a magnetic momentum of 6.0 μB. An Arrott plot analysis indicates that the Curie temperature TC of ferromagnetic ordering is about 10.1 K. Moreover, the saturated magnetic moment at 7 T and there being no clear hysteresis in the magnetic hysteresis loops suggest that EuB6 is a relatively soft ferromagnet. The electron transport measurements of the nanowire devices reveal that EuB6 nanowires have a lower output current and a higher resistance compared with bulk crystals, and may be useful for the future magnetic devices.

Domain Wall Motion Across Magnetic and Spin Compensation Points in Magnetic Garnets

Ferrimagnetic materials represent unique systems where the ease of manipulating the spins with applied magnetic fields is combined with exchange-driven acceleration of the internal spin dynamics. Of particular interest is the temperature range around the magnetic and spin compensation points, finely balancing both magnetic moment and angular momentum of the system, and leading to a very particular character of magnetic switching by the domain wall motion. Here we present our studies of the temperature-dependent domain wall dynamics in the temperature range covering both angular momentum and magnetization compensation points in garnet film, and reaching up to the Curie temperature. Drastic difference in the domain wall mobility and maximum achievable velocity in the vicinities of these two compensation points is demonstrated. Also a remarkably high mobility in weak applied magnetic fields is indicated.

From noninteracting to interacting picture of quark–gluon plasma in the presence of a magnetic field and its fluid property

We have attempted to build a parametric-based simplified and analytical model to map the interaction of quarks and gluons in the presence of magnetic field, which has been constrained by quark condensate and thermodynamical quantities like pressure, energy density, etc., obtained from the calculation of lattice quantum chromodynamics (QCDs). To fulfill that mapping, we have assumed a parametric temperature and magnetic field-dependent degeneracy factor, average energy, momentum and velocity of quarks and gluons. Implementing this QCD interaction in calculation of transport coefficient at finite magnetic field, we have noticed that magnetic field and interaction both are two dominating sources, for which the values of transport coefficients can be reduced. Though the methodology is not so robust, but with the help of its simple parametric expressions, one can get a quick rough estimation of any phenomenological quantity, influenced by temperature and magnetic field-dependent QCD interaction.

Magnetic Anisotropy and Damping Constant of Ferrimagnetic GdCo Alloy near Compensation Point.

Metallic ferrimagnets with rare earth-transition metal alloys can provide novel properties that cannot be obtained using conventional ferromagnets. Recently, the compensation point of ferrimagnets, where the net magnetization or net angular momentum vanishes, has been considered a key aspect for memory device applications. For such applications, the magnetic anisotropy energy and damping constant are crucial. In this study, we investigate the magnetic anisotropy and damping constant of a GdCo alloy, with a Gd concentration of 12–27%. By analyzing the equilibrium tilting of magnetization as a function of the applied magnetic field, we estimate the uniaxial anisotropy to be 1–3 × 104 J m−3. By analyzing the transient dynamics of magnetization as a function of time, we estimate the damping constant to be 0.08–0.22.

Response of a weakly magnetized hot QCD medium to an inhomogeneous electric field

The electric charge transport in a weakly magnetized hot QCD medium has been investigated in the presence of an external inhomogeneous electric field. The current densities (electric and Hall) induced by the inhomogeneous electric field have been estimated in the regime where space-time inhomogeneity of the field is small so that the collisional effect in the medium cannot be neglected. The collisional aspect of the medium has been captured by employing both a relaxation-time approximation and a Bhatnagar-Gross-Krook collision kernel in the relativistic Boltzmann equation. The magnetic field, momentum anisotropy, and quark chemical potential dependences of the electric current and Hall current densities have been explored, and the impacts on the respective conductivities have been studied. The inhomogeneities of the field are seen to have sizable effects on the electromagnetic responses of the collisional medium.

Orbital: An Electric and Magnetic Field

Quantum mechanics is a non-intuitive subject which is very difficult to understand. Various investigations have been done on understanding the basic quantum mechanics. Nevertheless, many attempts have been made for understanding the appropriate techniques, which are known to help conceptual under-standing of basics of orbital. As per the study the orbital is considered as an electric and magnetic field. The electric and magnetic field gets generated due to the continuous motion of electrons. So the orbital is nothing more than an electric and magnetic field. It is because of the electric and magnetic field of the orbital that it possesses electric and magnetic momentum. So taking all these points into consideration, it could be concluded that an orbital is no more than an electric and magnetic field.

Chromospheric Activity of Periodic Variable Stars Based on the LAMOST Low- and Medium-resolution Spectral Survey

Abstract We present a catalog of 75,867 periodic variable stars from data release 7 of the Large Sky Area Multi-Object Fiber Spectroscopic Telescope. We calculated the chromospheric activity index, equivalent widths for 201,349 spectra, and excess fractional luminosity ( R H α ′ ) for 130,796 spectra. Based on the intensity of the Hα line, we detected 30,719 F-, G-, and K-type variable stars with Hα fill-in or emission and 2521 M-type variable stars exhibiting Hα emission. Furthermore, 14,938 out of 30,573 periodic variable stars showed Hα variability. Analysis of samples with different spectral types confirmed that the activity fraction of stars with later spectral type clearly decreases as the absolute Galactic height increases away from the Galactic plane. The results also show that at the same absolute Galactic height, the activity fractions in eclipsing binaries are higher than those in single stars. In this study, we present the activity–rotation relations for F-, G-, K-, and M-type variable stars. The results of analysis show that rapid rotators keep a saturated value, and the absolute value of the power-law index exhibits an increasing trend from F- to K-type stars in the unsaturated regime. Moreover, we confirm that the angular momentum and magnetic momentum are positively correlated, which indicates that the α–ω dynamo may be working. In addition, we confirmed the correlations among the Hα, Hβ, Hγ, Hδ, Ca ii H&K, and Ca ii infrared triplet lines.

Image of the Electron Suggested by Nonlinear Electrodynamics Coupled to Gravity

We present a systematic review of the basic features that were adopted for different electron models and show, in a brief overview, that, for electromagnetic spinning solitons in nonlinear electrodynamics minimally coupled to gravity (NED-GR), all of these features follow directly from NED-GR dynamical equations as model-independent generic features. Regular spherically symmetric solutions of NED-GR equations that describe electrically charged objects have obligatory de Sitter center due to the algebraic structure of stress–energy tensors for electromagnetic fields. By the Gürses-Gürsey formalism, which includes the Newman–Janis algorithm, they are transformed to axially symmetric solutions that describe regular spinning objects asymptotically Kerr–Newman for a distant observer, with the gyromagnetic ratio g=2. Their masses are determined by the electromagnetic density, related to the interior de Sitter vacuum and to the breaking of spacetime symmetry from the de Sitter group. De Sitter center transforms to the de Sitter vacuum disk, which has properties of a perfect conductor and ideal diamagnetic. The ring singularity of the Kerr–Newman geometry is replaced with the superconducting current, which serves as the non-dissipative source for exterior fields and source of the intrinsic magnetic momentum for any electrically charged spinning NED-GR object. Electromagnetic spinning soliton with the electron parameters can shed some light on appearance of a minimal length scale in the annihilation reaction e+e−→γγ(γ).

Electron liquid state in the symmetric Anderson lattice

Using mean field approach, we provide analytical and numerical solution of the symmetric Anderson lattice for arbitrary dimension at half filling. The symmetric Anderson lattice is equivalent to the Kondo lattice, which makes it possible to study the behavior of an electron liquid in the Kondo lattice. We have shown that, due to hybridization (through an effective field due to localized electrons) of electrons with different spins and momenta mathbf{k} and mathbf{k} +overrightarrow{pi }, the gap in the electron spectrum opens at half filling. Such hybridization breaks the conservation of the total magnetic momentum of electrons, the spontaneous symmetry is broken. The state of electron liquid is characterized by a large Fermi surface. A gap in the spectrum is calculated depending on the magnitude of the on-site Coulomb repulsion and value of s–d hybridization for the chain, as well as for square and cubic lattices. Anomalous behavior of the heat capacity at low temperatures in the gapped state, which is realized in the symmetric Anderson lattice, was also found.

A program for simplifying summation of Wigner 3[formula omitted]-symbols

The program presented in this paper aims to simplify formulas involving products of a large amount of Wigner 3j-symbols summed over various magnetic quantum numbers. The algorithm used in our program is based on the graphical techniques originally developed by Yutsis, Levinson, and Vanagas, and later revised by some others. The output of our program is expressed as a weighted sum of products of 3j-, 6j- and 9j-symbols, with appropriate phase factors embedded. Compared with the previous literature, the present program is more flexible in a sense that it can deal with not only closed diagrams, such as the angular momentum recoupling coefficients, but also open diagrams. Our program is particularly useful to high precision atomic and molecular structure calculations using correlated electron–electron coordinates. Program summaryProgram Title: Reduce3jCPC Library link to program files:https://doi.org/10.17632/9zmx4b5sdd.1Licensing provisions: BSD 3-clauseProgramming language: Python 3.6.5Nature of problem: In atomic and molecular structure calculations, one often encounters expressions containing products of a large amount of Wigner 3j-symbols summed over various magnetic quantum numbers. It is desirable to simplify these expressions to make the final results compact, which is the goal of this paper.Solution method: The program uses the graphical techniques of quantum mechanical angular momentum theory, originally developed by Yutsis, Levinson, and Vanagas, and later modified by Brink and Satchler. The program is implemented in Python language, with its package “Networkx” extensively used. A friendly graphical input and output interface is developed. The input can be either a recoupling coefficient or an arbitrary expression containing products of the 3j-symbols summed over various magnetic quantum numbers. A strategically designed optimization method is also developed to help achieve our goal. Our program has significantly expanded the scope of usefulness of the existing programs so that it can now meet most of the demands from high precision atomic and molecular structure calculations.Additional comments including restrictions and unusual features: Reduce3j can effectively handle any open or closed graph, as long as the graph has more than one free line, and all the magnetic angular momentum quantum numbers from internal lines are summed over.

Design of quantum sensor to duplicate European Robins navigational system

In this article, we design a quantum device to duplicate the European Robins procedure to precisely determine the migratory route. In the mentioned procedure, the important issue is the geomagnetic field effect on the magnetic momentum of the created radical pairs (triplet-singlet states) dancing with a special frequency. To duplicate the procedure, a quantum sensor consisting of two coincident tripartite systems is designed. Each tripartite system is independently excited with the entangled photons (signal and idler). The interesting point is that by manipulation of the system in the right condition, the microwave cavities modes separately affected by the entangled photons can be entangled. The entangled microwave photons play the same role as the triplet-singlet states present in the bird’s navigational system. The key point in the design of the quantum sensor is that the entanglement between microwave photons can be strongly affected by the external magnetic field. In fact, this is the criterion employed by the quantum sensor to sense the magnetic field intensity and the direction. To analyze the system, the canonical quantization (or microscopic) method is used to determine the sensor’s Hamiltonian, and also the system dynamics equations of motions are analytically derived using Heisenberg-Langevin equations.

Effect of Ni doping on optical, structural, and morphological properties of ZnO thin films synthesized by MSILAR: Experimental and DFT study

In this study the thin films of Zinc Oxide (ZnO) and Nickel (Ni) doped ZnO were successfully synthesized by the simple modified successive ion layer adsorption and reaction method, with 30 cycles of dipping a substrate directly in cationic and anionic precursors without rinsing in water. The effect of nickel doping with this method was investigated. The X-ray diffraction (XRD) analysis confirms the wurtzite structure of ZnO in the thin films, without any secondary phases. A decrease in grain size and cell parameters was observed. Scanning electron microscopy (SEM) with energy dispersive X-Ray (EDX) analysis showed that Ni significantly affects the morphology of thin films. UV-visible spectra are obtained in the wavelength range between 300 nm to 1100 nm. A decrease in band gap from 3.23 eV to 3.11 eV was observed. First principal calculation was used to reveal the effect of Ni on electronic and magnetic properties. It showed that ZnO and Ni doped ZnO exhibits a direct band gap semiconductor and Ni-3d electrons are the primary source of magnetic momentum in ZnO matrix.

The Volume-complete Sample of M Dwarfs with Masses 0.1 ≤ M/M⊙ ≤ 0.3 within 15 Parsecs

Abstract M dwarfs with masses 0.1 ≤ M/M ⊙ ≤ 0.3 are under increasing scrutiny because these fully convective stars pose interesting astrophysical questions regarding their magnetic activity and angular momentum history. They also afford the most accessible near future opportunity to study the atmospheres of terrestrial planets. Because they are intrinsically low in luminosity, the identification of the nearest examples of these M dwarfs is essential for progress. We present the volume-complete, all-sky list of 512 M dwarfs with masses 0.1 ≤ M/M ⊙ ≤ 0.3 and with trigonometric distances placing them within 15 pc (π trig ≥ 66.67 mas) from which we have created a sample of 413 M dwarfs for spectroscopic study. We present the mass function for these 512 M dwarfs, which increases with decreasing stellar mass in linear mass space, but is flat in logarithmic mass space. As part of this sample, we present new V J R KC I KC photometry for 17 targets, measured as a result of the RECONS group’s long-term work at the CTIO/SMARTS 0.9 m telescope. We also note the details of targets that are known to be members of multiple systems and find a preliminary multiplicity rate of 21% ± 2% for the primary M dwarfs in our sample when considering known stellar and brown dwarf companions at all separations from their primaries. We further find that 43 ± 2% of all M dwarfs with masses 0.1 ≤ M/M ⊙ ≤ 0.3 are found in multiple systems with primary stars of all masses within 15 pc.

A New Theory for the Essence and Origin of Electron Spin

Spin is an intrinsic form of angular momentum carried by elementary particles, composite particles, and atomic nuclei. It is wildly believed that spin is a purely quantum mechanical concept and has no classical analogue. In fact, elementary particles are conceived as point objects which have no axis to “spin” around. Therefore, there is no explaining how spin arises at the fundamental level, why particles have the values they do, and what underpins the Pauli Exclusion principle and Bose-Einstein behavior. However, spin is like a vector quantity; it has a definite magnitude, and it has a “direction”, in order to spin should be composite. In this paper we propose a physical explanation for spin of the electron at the sub-particle level, relying on the vortex model of the electron. The electron is described as a superfluid frictionless vortex which has a mass, angular momentum and spin to provide a complete explanation of all properties of the electron: it composite, spinning around its own axis, produces a tiny magnetic fields independent of those from its orbital motions. The classical hydrodynamic laws are used to describe the quantum properties of the electron, such as spin, angular momentum, magnetic momentum and a magnetic dipole. The circulation in the vortex is constant, and the angular momentum of the vortex is conserved and has the same value of Planck constant. The direction of the angular momentum of a spinning electron vortex is along the axis of rotation and determined by the direction of spin. The spin quantum number 1/2 has a fixed value which represents the gap between the circulation rate of the core of the vortex and the boundaries of the vortex. The changeable values +1/2 “spin-up” or -1/2 “spin-down” indicate the direction of the magnetic dipole of the vortex. The relation between spin and Planck constant is discussed and the origin h/4pi angular momentum units are revealed.

About the Nature of the Quantum System—An Examination of the Random Discontinuous Motion Interpretation of the Quantum Mechanics

What is the quantum system? Consider the wave-function of the electron—what we call “single particle wave-function”—and assume that it contains N wave-packets. If we pass all the wave-packets through an electric field, all are deflected, as if each one of them contains an electron. However, if we bring any two wave-packets to travel close to one another, they don’t repel one another, as if at least one of them contains no charge. In trying to solve the measurement problem of the quantum mechanics (QM), different interpretations were proposed, each one coming with a particular ontology. However, only one interpretation paid explicit attention to the contradiction mentioned above. This interpretation was proposed by S. Gao who named it “random discontinuous motion” (RDM), because it assumes the existence of a particle that jumps from place to place at random. The particle carries all the physical properties of the respective type of particle, mass, charge, magnetic momentum, etc. It jumps under the control of an “instantaneous condition” about which Gao did not give details so far. Along with presenting problems of the QM that this interpretation solves, this text reveals difficulties vis-a-vis entanglements and the special relativity.

Antithetic Magnetic and Shadow Hamiltonian Monte Carlo

Hamiltonian Monte Carlo is a Markov Chain Monte Carlo method that has been widely applied to numerous posterior inference problems within the machine learning literature. Markov Chain Monte Carlo estimators have higher variance than classical Monte Carlo estimators due to autocorrelations present between the generated samples. In this work we present three new methods for tackling the high variance problem in Hamiltonian Monte Carlo based estimators: 1) We combine antithetic and importance sampling techniques where the importance sampler is based on sampling from a modified or shadow Hamiltonian using Separable Shadow Hamiltonian Hybrid Monte Carlo, 2) We present the antithetic Magnetic Hamiltonian Monte Carlo algorithm that is based on performing antithetic sampling on the Magnetic Hamiltonian Monte Carlo algorithm and 3) We propose the antithetic Magnetic Momentum Hamiltonian Monte Carlo algorithm based on performing antithetic sampling on the Magnetic Momentum Hamiltonian Monte Carlo method. We find that the antithetic Separable Shadow Hamiltonian Hybrid Monte Carlo and antithetic Magnetic Momentum Hamiltonian Monte Carlo algorithms produce effective sample sizes that are higher than antithetic Hamiltonian Monte Carlo on all the benchmark datasets. We further find that antithetic Separable Shadow Hamiltonian Hybrid Monte Carlo and antithetic Magnetic Hamiltonian Monte Carlo produce higher effective sample sizes normalised by execution time in higher dimensions than antithetic Hamiltonian Monte Carlo. In addition, the antithetic versions of all the algorithms have higher effective sample sizes than their non-antithetic counterparts, indicating the usefulness of adding antithetic sampling to Markov Chain Monte Carlo algorithms. The methods are assessed on benchmark datasets using Bayesian logistic regression and Bayesian neural network models.

Spin and orbital angular momentum dynamics in counterpropagating vectorially structured light

It is well-known that electric spin angular momentum and electric orbital angular momentum are conserved under paraxial propagation of travelling waves in free-space. Here we study the electric and magnetic angular momentum in counter-propagating waves and show both theoretically and experimentally that neither component alone is conserved except in special cases. We attribute this non-conservation to spin-spin and orbit-orbit coupling between the electric and magnetic fields. This work generalises previous findings based on travelling waves, explains the apparent spin-orbit coupling in counter-propagating paraxial light, and broadens our understanding of angular momentum conservation in arbitrary structured light waves.

An observational correlation between magnetic field, angular momentum and fragmentation in the envelopes of Class 0 protostars?

Aims. The main goal of the following analysis is to assess the potential role of magnetic fields in regulating the envelope rotation, the formation of disks and the fragmentation of Class 0 protostars in multiple systems. Methods. We use the Submillimeter Array to carry out observations of the dust polarized emission at 0.87 mm, in the envelopes of a large sample of 20 Class 0 protostars. We estimate the mean magnetic field orientation over the central 1000 au envelope scales to characterize the orientation of the main component of the organized magnetic field at the envelope scales in these embedded protostars. This direction is compared to that of the protostellar outflow in order to study the relation between their misalignment and the kinematics of the circumstellar gas. The latter is traced via velocity gradient observed in the molecular line emission (mainly N2H+) of the gas at intermediate envelope scales. Results. We discover a strong relationship between the misalignment of the magnetic field orientation with the outflow and the amount of angular momentum observed at similar scales in the protostellar envelope, revealing a potential link between the kinetic and the magnetic energy at envelope scales. The relation could be driven by favored B-misalignments in more dynamical envelopes or a dependence of the envelope dynamics with the large-scale B initial configuration. Comparing the trend with the presence of fragmentation, we observe that single sources are mostly associated with conditions of low angular momentum in the inner envelope and good alignment of the magnetic field with protostellar outflows, at intermediate scales. Our results suggest that the properties of the magnetic field in protostellar envelopes bear a tight relationship with the rotating-infalling gas directly involved in the star and disk formation: we find that it may not only influence the fragmentation of protostellar cores into multiple stellar systems, but also set the conditions establishing the pristine properties of planet-forming disks.