Inhomogeneous External Magnetic Field Research Articles

Quantum skyrmion dynamics studied by neural network quantum states

We study the dynamics of quantum skyrmions under a magnetic field gradient using neural network quantum states. First, we obtain a quantum skyrmion lattice ground state using variational Monte Carlo with a restricted Boltzmann machine as the variational ansatz for a quantum Heisenberg model with a Dzyaloshinskii-Moriya interaction. Then, using the time-dependent variational principle, we study the real-time evolution of quantum skyrmions after a Hamiltonian quench with an inhomogeneous external magnetic field. We show that field gradients are an effective way of manipulating and moving quantum skyrmions. Furthermore, we demonstrate that quantum skyrmions can decay when interacting with each other. This work shows that neural network quantum states offer a promising way of studying the real-time evolution of quantum magnetic systems that are outside the realm of exact diagonalization. Published by the American Physical Society 2024

Structure, control, and dynamics of altermagnetic textures

We present a phenomenological theory of altermagnets, that captures their unique magnetization dynamics and allows modeling magnetic textures in this new magnetic phase. Focusing on the prototypical d-wave altermagnets, e.g., RuO2, we can explain intuitively the characteristic lifted degeneracy of their magnon spectra, by the emergence of an effective sublattice-dependent anisotropic spin stiffness arising naturally from the phenomenological theory. We show that as a consequence the altermagnetic domain walls, in contrast to antiferromagnets, have a finite gradient of the magnetization, with its strength and gradient direction connected to the altermagnetic anisotropy, even for 180° domain walls. This gradient generates a ponderomotive force in the domain wall in the presence of a strongly inhomogeneous external magnetic field, which may be achieved through magnetic force microscopy techniques. The motion of these altermagentic domain walls is also characterized by an anisotropic Walker breakdown, with much higher speed limits of propagation than ferromagnets but lower than antiferromagnets.

Enhanced plasma ion heating by lasers in inhomogeneous external magnetic field

Particle–In–Cell simulations have been carried out to study the propagation of a laser pulse inside a plasma medium threaded with an external magnetic field. The external magnetic field is chosen to have space variations, which ensure that the laser pulse penetrates inside the plasma slab following the pass band dispersion relation of the X-mode. The spatial variation of the magnetic field is chosen such that the LH resonance is encountered within the bulk plasma medium. Enhanced deposition of laser energy to ions at the resonance layer has been demonstrated. This scheme would thus be useful to heat ions at any desired bulk region of the plasma.

Dust magnetoacoustic waves in an inhomogeneous cylindrical four-component dusty plasma in the presence of polarization force

Abstract Dust magnetoacoustic waves have been examined in an inhomogeneous, bounded, cylindrical dusty plasma containing oppositely polarized dust particles. Considering polarization force, dust dynamics in r − θ plane is studied in the presence of inhomogeneous external magnetic field along z axis. At equilibrium, the dusty plasma components are supposed to follow Gaussian density distribution. Using reductive perturbation method (RPM), a variable coefficient cylindrical Kadomtsev–Petviashvili (VCCKP) equation has been derived. For weak azimuthal perturbation, an analytical solution, obtained by Zhang (“Exact solutions of a kdv equation with variable coefficients via exp-function method,” Nonlinear Dynam., vol. 52, nos. 1–2, pp. 11–17, 2008) using Exp-function method, is chosen. Phase velocity of dust magnetoacoustic wave is found to be modified by the density inhomogeneities, polarization force, dust charge state ratio and ion-to-electron temperature ratio. Spatio-temporal evolution of the dust number densities has been noticed. Existence of the compressive electromagnetic solitary waves is observed numerically for the chosen dusty plasma parameter range. The impacts of the inhomogeneity, polarization force, dust charge state ratio and ion-to-electron temperature ratio on the relative amplitude of the dust magnetoacoustic wave are also discussed.

Local quantum Fisher information and local quantum uncertainty for general X states

A two-spin-1/2 Heisenberg XYZ model with Dzyaloshinsky–Moriya (DM) and Kaplan–Shekhtman–Entin-Wohlman–Aharony (KSEA) interactions in the presence of an inhomogeneous external magnetic field is considered at thermal equilibrium. Its density matrix has the general X form for which we derive explicit formulas for the local quantum Fisher information (LQFI) and local quantum uncertainty (LQU) directly in terms of model parameters. This allows us to perform a comparative study for the discord-type quantum correlations LQFI and LQU and to reveal a number of new features in their behavior. In particular, the sudden transitions of quantum correlations with a smooth change in temperature are found. Moreover, it is shown that there may be a sequence of such transitions for certain choices of interaction constants.

Transverse expansion of (1 + 2) dimensional magneto-hydrodynamics flows with longitudinal boost invariance

In the present work, we investigate the effects of the magnetic field on expanding hot and dense nuclear matter as an ideal fluid. We consider QGP, in the particular case of a (1 + 2) dimensional longitudinally boost-invariant fluid expansion, in the background of an inhomogeneous magnetic field that is generated by external sources. We assume the magnetic field points in the direction perpendicular to the reaction plane, follows the power-law decay in proper time, and has two components on the transverse plane. To simplify our calculation, we suppose the investigated fluid has azimuthal symmetry, and magneto-hydrodynamic equations are described in a polar coordinate system on the transverse plane of reaction. Our results depict the space-time evolution of the transverse expansion of the fluid in the presence of an inhomogeneous external magnetic field. Moreover, we show when the magnetic field decays in proper time τ with a power-law τn/2(n<1), two distinct solutions can be found depending on the values of n. We show that n<−2 gives rise to the physical scenario whereas the n>−2 leads to non-physical results.

Mode conversion and laser energy absorption by plasma under an inhomogeneous external magnetic field.

The interaction of a high-frequency laser with plasma in the presence of an inhomogeneous external magnetic field has been studied here with the help of particle-in-cell simulations. It has been shown that the laser enters the plasma as an extraordinary wave (X-wave), where the electric field of the wave oscillates perpendicular to both the external magnetic field and propagation direction and as it travels through the plasma, its dispersion property changes due to the inhomogeneity of the externally applied magnetic field. Our study shows that the X-wave's electromagnetic energy is converted to an electrostatic mode as it encounters the upper-hybrid (UH) resonance layer. In the later stage of the evolution, this electrostatic wave breaks and converts its energy to electron kinetic energy. Our study reveals two additional processes involved in decay of the electrostatic mode at the UH resonance layer. We have shown that the energy of the electrostatic mode at the upper-hybrid resonance layer also converts to a low-frequency lower-hybrid mode and high-frequency electromagnetic harmonic radiations. The dependence of energy conversion processes on the gradient of the external magnetic field has also been studied and analyzed.

Stability of Spin-Wave Solitons in Bose-Einstein Condensates of Magnons: A Possible Application in Ferromagnetic Films.

In this paper, we theoretically investigate the stability of spin-wave solitons in Bose-Einstein condensates of repulsive magnons, confined by an inhomogeneous external magnetic field described by a Gaussian well. For this purpose, we use the quasi-one-dimensional Gross-Pitaevskii equation to describe the behavior of the condensate. In order to solve the Gross-Pitaevskii equation, we used two different approaches: one analytical (variational method) and another numerical (split-step Crank-Nicolson method). The stability of the solutions and the validation of the numerical results were confirmed, respectively, through the anti-VK criterion and the virial theorem. Furthermore, the simulations described the behavior of physical quantities of interest such as chemical potential, energy per magnon and central density as a function of the nonlinearity of the model (magnon-magnon interactions). The theoretical results provide subsidies for a better understanding of the nonlinear phenomena related to the Bose-Einstein condensates of magnons in ferromagnetic films.

Ring dust structures in a weak inhomogeneous magnetic field

AbstractExperimental results on the influence of an external inhomogeneous magnetic field created in the end areas of the coil on the dynamics of a ring‐shaped dust structure in a stratified glow discharge in argon are presented. The rotational behaviour of the ring was investigated at different magnetic fields in the range up to 16 mT. It was found that the direction of rotational motion of dust particles in an inhomogeneous magnetic field depends on the direction of its radial component. A theoretical model was proposed to explain the experimental observations.

Spinor condensate in spin–orbit coupled Bose gases with inhomogeneous magnetic field

In this paper, we study the dynamic properties of spin–orbit coupling (SOC) spin-1 antiferromagnetic Bose–Einstein condensates with inhomogeneous external magnetic field by numerical simulations of the multicomponent Gross–Pitaevskii equation. Our results show that the spin dynamics process is greatly affected by SOC when the system is in the absence of magnetic field. The periodicity of spin exchange dynamics disappears and the population of thermal clouds for [Formula: see text] and [Formula: see text] gradually increases and decreases and then reaches a steady value. In this case, a stable stripe phase emerges for three-component wavefunction. Nevertheless, the spin dynamics process becomes complex in the presence of magnetic field, depending on the competition between magnetic field and SOC. The influences of SOC are masked by the relatively strong magnetic field and the density structures are similar to the case of without or weak magnetic field.

Influences of spin–orbit interaction on quantum speed limit and entanglement of spin qubits in coupled quantum dots

Quantum speed limit and entanglement of a two-spin Heisenberg XYZ system in an inhomogeneous external magnetic field are investigated. The physical system studied is the excess electron spin in two adjacent quantum dots. The influences of magnetic field inhomogeneity as well as spin–orbit coupling are studied. Moreover, the spin interaction with surrounding magnetic environment is investigated as a non-Markovian process. The spin–orbit interaction provides two important features: the formation of entanglement when two qubits are initially in a separated state and the degradation and rebirth of the entanglement.

Magnetic-Field-Driven Antiferromagnetic Domain Wall Motion

We theoretically study the antiferromagnetic domain wall motion actuated by an inhomogeneous external magnetic field. The Lagrangian and the equations of motion of antiferromagnetic spins under an inhomogeneous magnetic field are derived, first in terms of the N\'eel vector, and then using collective coordinates of the domain wall. A solution is found that describes the actuation of a domain wall by an inhomogeneous field, in which the motion is initiated by a paramagnetic response of wall magnetization, which is then driven by a Stern-Gerlach like force. The effects of pinning potential are also investigated. These results are in good agreement with atomistic simulations. While the present formulation contains the so-called intrinsic magnetization associated with N\'eel texture, a supplementary discussion is given to reformulate the theory in terms of physical magnetization without the intrinsic magnetization.

Quasiphotons for the Nonstationary 2D Dirac Equation

Asymptotic expansions are obtained for the solution of the (2+1)-dimensional nonstationary Dirac equation describing the wave function of a massive fermion in graphene, placed in an external inhomogeneous electric and magnetic field. The semiclassical asymptotics of the solution of the Cauchy problem for this equation with rapidly oscillating and rapidly decreasing initial data are found. This made it possible to find quasiphotons asymptotic solutions describing Gaussian wave packets concentrated near a point running along a semiclassical trajectory.

Electrical magnetochiral effect and kinetic magnetoelectric effect induced by chiral exchange field in helical magnetics

The features of spin and charge transport in conductive helimagnets, which are due to the action of an inhomogeneous exchange magnetic field on the spin of conduction electrons, are theoretically studied. The interaction between the spin of moving particles and an inhomogeneous external magnetic field was first recorded in the famous Stern-Gerlach experiment that investigated the quantum nature of spin. In the present paper, we have demonstrated that two physical effects---the electrical magnetochiral effect (EMChE) and the kinetic magnetoelectric effect (KMEE)---can be explained through the interaction of the spins of itinerant electrons in chiral helimagnets with spatially inhomogeneous effective magnetic field of exchange origin. All parameters of the EMChE and KMEE are presented in terms of both the characteristic frequencies of spin relaxation of conduction electrons in a helimagnet and the frequencies of their Larmor precession in external and internal exchange fields. It has been shown that the effective frequency of conduction-electron spin relaxation in a helimagnet contains three components: (i) the rate of spin-lattice relaxation caused by spin-orbit scattering of conduction electrons by defects of the crystal lattice, (ii) the rate of change in the average spin of electrons due to their ``diffusion'' escape from a region with a given direction of the average spin to a region with a different direction of spin density, and (iii) the contribution of the Larmor precession of the spins of electrons moving in the helimagnet's exchange field that assigns the precession axis altering its direction in space. The peculiarities of the EMChE and KMEE that substantially depend on the ratio of the above-listed spin relaxation rates and the angular frequencies of electron precession are described. The numerical estimates performed show that the mechanism of generating EMChE provides the effect magnitude sufficient to be experimentally detected in metallic helimagnets. The frequency regions of spin relaxation and spin precession are determined to observe a giant electrical magnetochiral effect and resonant behavior of the chiral magnetoresistance. We have called the appropriate effect ``magnetochiral kinetic resonance'' (MChKR). The physical nature of MChKR is elucidated. The latter arises due to the coincidence of the Larmor precession frequency of an electron in the effective field and the phase change frequency of the helicoidal exchange field acting on the electron moving along the helicoid's axis with a speed equal to that of the electron flow. We have demonstrated how the experimental studies of the KMEE can be used to directly determine the chirality of helimagnets.

A Domain Dynamic Model Study of Magneto-impedance Sensor in the Presence of Inhomogeneous Magnetic Fields

We investigate the effect of an inhomogeneous external magnetic field and magnetization on magneto-impedance (MI) effect based on the domain dynamic model. The impedance (Z) of a thin magnetic layer under different field inhomogeneity and magnetization inhomogeneity (FIH/MIH) profiles is calculated. The MI effect determined in different frequencies shows fixed MI peak location when field and magnetization are homogeneous. However, for the cases of FIH/MIH conditions, the locations of the peaks are changed for different frequencies and layer thicknesses. The MI peaks are broadened due to the FIH profile since not all domains rotate uniformly as the field changes along the length of the layer. In the case of MIH, the values of impedance are decreased more than those of FIH (maximally about 8% at peak positions), and the MI peak positions have less shifted to higher field values (maximally about 25%) in comparison with the FIH peak positions. In the case of FIH and MIH, our calculations show the maximum relative change in the impedance peak position of about 12%. The obtained results present useful information for improving the performance of future magnetic sensors which work based on the MI effect.

On the Issue of Damping of a Transverse Ion Bernstein Wave in an Inhomogeneous Magnetic Field

With allowance for the centrifugal and gradient drifts of ions, a new approximate dispersion equation is obtained for the ion Bernstein (IB) wave propagating strictly transverse to the external inhomogeneous magnetic field. Using this equation, it is shown that if, in the high-temperature plasma, the drift of ions is taken into account, the resonance frequency ranges in the vicinities of the ion cyclotron frequency harmonics can strongly overlap. In this case, the ion Bernstein waves turn out to be strongly damped, despite the absence of the longitudinal component of the wave vector.

Solving systems of linear algebraic equations via unitary transformations on quantum processor of IBM Quantum Experience

We propose a protocol for solving systems of linear algebraic equations via quantum mechanical methods using the minimal number of qubits. We show that $(M+1)$-qubit system is enough to solve a system of $M$ equations for one of the variables leaving other variables unknown provided that the matrix of a linear system satisfies certain conditions. In this case, the vector of input data (the rhs of a linear system) is encoded into the initial state of the quantum system. This protocol is realized on the 5-qubit superconducting quantum processor of IBM Quantum Experience for particular linear systems of three equations. We also show that the solution of a linear algebraic system can be obtained as the result of a natural evolution of an inhomogeneous spin-1/2 chain in an inhomogeneous external magnetic field with the input data encoded into the initial state of this chain. For instance, using such evolution in a 4-spin chain we solve a system of three equations.

Free and Forced Oscillations of Magnetic Liquids Under Low-Gravity Conditions

Abstract The sloshing of liquids in microgravity is a relevant problem of applied mechanics with important implications for spacecraft design. A magnetic settling force may be used to avoid the highly non-linear dynamics that characterize these systems. However, this approach is still largely unexplored. This paper presents a quasi-analytical low-gravity sloshing model for magnetic liquids under the action of external inhomogeneous magnetic fields. The problems of free and forced oscillations are solved for axisymmetric geometries and loads by employing a linearized formulation. The model may be of particular interest for the development of magnetic sloshing damping devices in space, whose behavior can be easily predicted and quantified with standard mechanical analogies.

Model of the microscroll structure

In this paper, we propose a method for the formation of TiO2 microscrolls due to the folding of thin layers in an external inhomogeneous magnetic field deposited on a glass substrate during laser ablation of a titanium target in the air. The models of the initial stages of the formation and structure of the microscrew are also proposed.

Transverse expansion of hot magnetized Bjorken flow in heavy ion collisions

We argue that the existence of an inhomogeneous external magnetic field can lead to radial flow in transverse plane. Our aim is to show how the introduction of a magnetic field generalizes the Bjorken flow. We investigate the effect of an inhomogeneous weak external magnetic field on the transverse expansion of in-viscid fluid created in high energy nuclear collisions. In order to simplify our calculation and compare with Gubser model, we consider the fluid under investigation to be produced in central collisions, at small impact parameter; azimuthal symmetry has been considered. In our model, we assume an inhomogeneous external magnetic field following the power-law decay in proper time and having radial inhomogeneity perpendicular to the radial velocity of the in-viscid fluid in the transverse plane; then the space time evolution of the transverse expansion of the fluid is obtained. We also show how the existence of an inhomogeneous external magnetic field modifies the energy density. Finally we use the solutions for the transverse velocity and energy density in the presence of a weak magnetic field, to estimate the transverse momentum spectrum of protons and pions emerging from the Magneto-hydrodynamic solutions.