Values Of External Magnetic Field Research Articles

Critical characteristics of spin − 1/2 four-leg nanotube: Monte Carlo Simulation

In this study, we aim to investigate theoretically the critical characteristics of spin −1/2 four-leg nanotube for the nanotechnology applications. The Ising model simulated by Monte Carlo simulation is adopted with the first exchange coupling J , the second exchange coupling between the second nearest neighbor atomic spins J ′ and the transverse exchange coupling J z , and the external magnetic field h as parameters. Herein, we examine the local properties of spin −1/2 four-leg nanotube by analyzing the magnetization, susceptibility and hysteresis loop behavior as function of J ′ , J Z and h . The obtained results show that the isotropic ‐ 1 / 2 four-leg nanotube Ising model presents critical behavior at ferromagnetic to paramagnetic phase transition where the Curie temperature T C increases according to vertical and second nearest neighbor exchange coupling. Furthermore, under external magnetic field, the magnetization keeps the second order transition and the magnetic susceptibility declines with the increase of applied external magnetic field value. In addition to that, we have found single ferromagnetic hysteresis loops, for which the shape increases by increasing the second nearest neighbor exchange coupling when T = J . Finally, the critical temperature shows perfect mirror symmetry relative to the vertical and increases with the second nearest neighbor exchange coupling.

Electronic transport of an extended Ising chain with competing thermal fluctuation and magnetic ordering

In this study, we investigate the behavior of spin-dependent electronic transport in a magnetic nanowire with thermal random oriented moments, connected to two similar (anti-) ferromagnetic leads. The model is based on Green’s function technique within the nearest neighbor tight-binding approach in the framework of canonical ensemble. We analyze the electronic transmission and its variance in different ordered and disordered regimes at a finite temperature in an external magnetic field. The results indicate that at nonzero temperatures, thermal fluctuation of moment orientations decreases the system’s electronic conductance, leading to a smooth conductance-energy relationship. Depending on temperature and external magnetic field values as well as Ising exchange interaction strength, the system can transit to an ordered phase. Additionally, the larger length of the interacting part affects the transmission coefficient and amplifies its variance. This study sheds light on the intricate interplay between temperature, magnetic field, and moment orientations in the context of spin-dependent electronic transport through magnetic nanowires, offering valuable insights into the usage of such systems.

ELECTROMAGNETIC DIPOLAR MODES IN MAGNETIZED NONUNIFORM PLASMA-VACUUM-METAL WAVEGUIDE

This article presents the results of theoretical study of the phase and attenuation properties of the dipolar electromagnetic modes in cylindrical plasma-vacuum-metal waveguide structure. Plasma is described in hydrodynamic approach and is supposed to be slightly non-uniform in axial direction and strongly non-uniform in radial direction. It was studied the influence of the external magnetic field value, the electron effective collision frequency and other waveguide parameters on the phase and attenuation properties of the considered waves.

Quark Condensate in QCD at Nonzero Magnetic Field and Temperature

The basic form of the quark condensate for arbitrary values of external magnetic field and temperature, is derived using the field equations with account of confinement. The resulting expression of the chiral condensate is shown to be proportional to square of the singlet $q\bar q$ ground state wave function at origin, $|\phi_0(0)|^2$. For light quarks without magnetic field the condensates are proportional to $\sigma^{3/2}$ ($\sigma$ is the string tension). Numerical results are presented in 5 Tables and shown to be in good agreement with the lattice data, both for nonzero magnetic field $eB$ and temperature $T$ in the range $0 <T < 120$~MeV,~ $0 <eB <4$~GeV$^2$.

Tunable photonic bandgap and reflection phase shift properties of 1D binary photonic crystal consisting of double negative and magnetic cold plasma materials

In this manuscript, by using alternate layers of double negative and magnetic cold plasma materials, we have studied the reflection and reflection phase shift properties of 1D binary photonic crystals. The simulations of the proposed work have been carried out by using the transfer matrix method with the help of MATLAB software. It has been found that the combination of the angle of incidence and external magnetic field under both right hand polarized and left handed polarized configurations can be used for right and left tuning of photonic bandgap (PBG) of the proposed structure under consideration. Under the aforementioned circumstances, the reflection phase shift corresponding to TE and TM waves can be smoothly switched between 0 to π and –π to 0, respectively, across PBGs of the proposed structure. The variation in external magnetic field values from 0 to 6 T and angle of incidence from 0° to 80° can be used for precise tuning of PBG and reflection phase shift between –π and π depending upon TM and TE polarization cases, respectively. This study may open a new gateway for designing externally tunable microwave devices like single to multichannel band-stop filters, buffers that can hold data temporarily, tunable wave plates, and tunable phase retarders.

Investigations on Strong-Tuned Magnetocaloric Effect in La0.5Ca0.1Ag0.4MnO3

The magnetocaloric effect (MCE) of La0.5Ca0.1Ag0.4MnO3 (LCAMO) is simulated using a phenomenological model (PM). The LCAMO MCE parameters are calculated as the results of simulations for magnetization vs. temperature at different values of external magnetic field (Hext). The temperature range of MCE in LCAMO grew as the variation in Hext increased, eventually covering the room temperature at high Hext values. The MCE of LCAMO is tunable with the variation of Hext, proving that LCAMO is practically more helpful as a magnetocaloric (MC) material for the development of magnetic refrigerators in an extensive temperature range, including room temperature and lower and higher ones. The MCE parameters of LCAMO are practically greater than those of some MC samples in earlier works.

Structural, electronic and magnetocaloric properties of antiskyrmion hosting Heusler compounds: Mn2PtSn and Mn1.4PtSn

In this work, we have studied the structure, electronic and magnetic properties of Mn2PtSn and Mn1.4PtSn by using the ab initio calculations and Monte Carlo study. The ab initio calculations, based on the functional theory of density combined with the method of linear augmented plane waves at potential, are performed to investigate both electronic and magnetic properties of the two compounds. The total and partial densities of two systems have been calculated. Mn1.4PtSn, the first known Heusler tetragonal (Mn vacancy-induced) superstructure compound, opens a new direction of research for superstructure-related properties in a family containing multiple compounds. We have deduced the total magnetic moment of the two systems. We observe an anisotropic fractal magnetic pattern of zero-field closing domains above the spin-reorientation transition temperature, which transforms into a set of high-field bubble domains. Below the spin-reorientation transition temperature, the strong in-plane anisotropy as well as the zero-field fractal self-affinity is gradually lost, while the formation of high-field bubble domains remains robust. The magnetization, specific heat and magnetic entropy change have been obtained by using the Monte Carlo simulations. The relative cooling power has been obtained for different values of external magnetic field and temperatures.

Magnetic skyrmions generation and control in FePt nanoparticles through shape and magnetocrystalline anisotropy variation: a finite elements method micromagnetic simulation study

Magnetic skyrmions created during magnetization reversal in cylindrical, reuleaux and polygon-based magnetic nanoparticles with perpendicular magnetocrystalline anisotropy (MCA) similar to that of partially chemically ordered FePt were studied using finite elements method micromagnetic simulations. Néel chiral stripes, horseshoe, labyrinth skyrmionic textures along with multiple skyrmions were unveiled in different systems generated by the variation of the MCA magnitude and the nanoparticles geometrical shape. These skyrmionic textures under certain conditions can be stable in a range of external magnetic fields and for different MCA values. Simulations revealed the inherent relation of skyrmionic states with nanoparticle geometry and the energy differences between successive external field values observed during the magnetization reversal process. Energetical transitions from non-skyrmionic to skyrmionic and from skyrmionic to different skyrmionic states were quantified and associated with the individual anisotropy, exchange and demagnetization energy contributions for the nanoparticles studied. Finally, the diameters of Néel type skyrmions created through the nanoparticle shape variation were reported for different MCA and external magnetic field values.

STABILITY OF SKYRMIONS IN THE FRUSTRATED ANTIFERROMAGNETIC/FERROELECTRIC BILAYERS WITH THE TRIANGULAR LATTICE

The formation and conditions of stability of a skyrmions at the interface between a ferroelectric layer and antiferromagnetic layer with triangilar lattice and its phase transition are studied. All interactions between spins and polarizations are limited to nearest neighbors (NN). The antiferromagnetic exchange interaction among the spins inside antiferromagnetic layer will compete with the perpendicular interface interaction between adjacent layers. The ground state spin configuration at zero temperature is calculated by using the numerical high performance steepest descent method. The resulting configuration is non-collinear. Small values of external field yields small values of angles between spins in the plane so that the ground state configurations have antiferromagnetic and non collinear domains. We observe the creation of single spin vortices. We noted that for zero applied magnetic field the skyrmions in the antiferromagnetic/ferroelectric bilayers with triangular lattice can be created in the region of interface magnetoelectric interaction value between 0.85 and 1.95. The strong external magnetic field applied perpendicular to the interface with non-collinear Dzyaloshinskiy-Morya-like magnetoelectric interaction at the interface leads to remove the skyrmion phase and magnetic phase transitions. With increasing the interface magnetoelectric coupling, the skyrmion lattice disappear. We found the formation perfect skyrmion structure at non-zero external magnetic field and moderate values of magnetoelectric interaction. The skyrmions structure is stable in a large region of the interface magnetoelectric interaction between antiferromagnetic and ferroelectric films. The results of Monte Carlo simulations that we carried out confirm that observed skyrmions are stable up to a finite temperature.

Kinetic equation having the integral scattering term with a linear form of external electrical and magnetic fields

In many cases, nobody consider any kinetic equation where the collision integral does not use clearly the values of external electric and magnetic fields. But there is some reason to use in the collision integral the above fields and to consider the ratio of the averaged deBroglie wavelength to the free-path length.

Analysis and Design of 460 GHz Microwave Gyrotron Oscillator

This paper is concerned with the analysis and design of a gyrotron oscillator with 460 GHz that can excite both modes (TE231) the fundamental (230GHz) and (TE061, TE261) second harmonic (near 460GHz). The oscillator is operated with 12KV beam voltage and 100mA beam current, and a computer program was developed to study the cavity in this oscillator and the wave-particle interaction inside it using the forward finite difference technique as a numerical method. The input data of the program are electron energy, velocity ratio, normalized cavity length, the normalized value of the external magnetic field, the mode number (m,n,l), and nth-non van shining root of J_m^' (x)=0 to calculate the beam and starting currents, frequency and quality factor of the cavity. The results show good agreement with other reported works [10]- [12]- [13]- [14], [15] .This oscillator can serve as a millimeter-wave source at the magnetic field of (16.4T) for enhanced nuclear magnetic resonance and can be used to perform the biological experiment.

Power absorption, plasma parameters and wave structure in inductive RF plasma source with low value external magnetic field

The efficiency of radio-frequency (RF) power absorption, RF magnetic field structure and plasma parameters were measured in cylindrical inductive RF plasma sources 20 cm in diameter and 22, 32, 53 cm in length with a low value external magnetic field. The experiments were carried out in argon at pressures of 13–140 mPa. The RF power supply changed from 200 W to 800 W. The spiral antenna was used for sustaining the discharge. It was shown that efficiency of RF power absorption depended nonlinearly on the external magnetic field values. At maximal values of the RF power absorption efficiency, the axial distributions of longitudinal Bz and azimuthal Bφ components of RF magnetic field manifested the formation of the partially standing wave with a half wavelength close to 8 cm. At the same conditions, the axial dependence of the radial RF magnetic field component Br differed drastically. It was concluded that the Bz and Bφ amplitudes were largely determined by the RF field of Trivelpiece-Gould wave, while Br amplitude represented the radial RF field of the helicon wave.

Thermodynamics and feature extraction by machine learning

Machine learning methods are powerful in distinguishing different phases of matter in an automated way and provide a new perspective on the study of physical phenomena. We train a Restricted Boltzmann Machine (RBM) on data constructed with spin configurations sampled from the Ising Hamiltonian at different values of temperature and external magnetic field using Monte Carlo methods. From the trained machine we obtain the flow of iterative reconstruction of spin state configurations to faithfully reproduce the observables of the physical system. We find that the flow of the trained RBM approaches the spin configurations of the maximal possible specific heat which resemble the near criticality region of the Ising model. In the special case of the vanishing magnetic field the trained RBM converges to the critical point of the Renormalization Group (RG) flow of the lattice model. Our results suggest an alternative explanation of how the machine identifies the physical phase transitions, by recognizing certain properties of the configuration like the maximization of the specific heat, instead of associating directly the recognition procedure with the RG flow and its fixed points. Then from the reconstructed data we deduce the critical exponent associated to the magnetization to find satisfactory agreement with the actual physical value. We assume no prior knowledge about the criticality of the system and its Hamiltonian.

Effect of external magnetic field on weld width and reinforcement height of shielded metal arc welded joints

Shielded metal arc welding process is one of the most utilized welding processes which are used to join structural components having good mechanical and structural properties. The macro-structure and the mechanical properties of the weld are closely related with each other. The external magnetic field can be applied in such a way that it can spread the molten arc materials. If the external magnetic field is along the direction of welding, the force on the molten electrode material will be normal to the bead direction. If alternative current is used for welding process, the external magnetic field will also be of alternative nature and the arc will be deflected towards both sides of the length of bead. Spreading of molten material increases the weld width and may reduce the reinforcement height. In this work the external magnetic field was produced with the help of a solenoid and the battery eliminator by passing the current through the coils of the solenoid. The heat and the material of arc are distributed to larger area and hence the bead is flattened due to magnetic field. After experimentation it was found that the weld bead width increases and reinforcement height decreases with increase in the value of external parallel magnetic field.

Ferromagnetic resonance in nanotwinned Ni–Mn–Ga film undergoing martensitic transformation

The ferromagnetic resonance (FMR) in the shape memory alloys (SMAs) exhibiting structural cubic-tetragonal phase transition has been studied. The influence of instability and spatial inhomogeneity of crystal lattice on the FMR spectra of twinned ferromagnetic SMAs films has been analyzed using statistical model of ferromagnetic martensite. It has been shown that the abnormally strong temperature dependence of lattice parameters of martensitic film gives a noticeable contribution to the temperature dependence of the resonance value of external magnetic field. The narrowing of the resonance peak, which had been experimentally observed on cooling of the film slightly below the Curie temperature, has been explained. It is argued that the martensitic films are good candidates for the experimental study of local elastic strains influence on the shape of the FMR peak.

Термодинамические свойства систем спинов Гейзенберга на квадратной решетке с взаимодействием Дзялошинского - Мория

We present results of numerical simulation of thermodynamics for array of Classical Heisenberg spins placed on 2D square lattice. By using Metropolis and Wang--Landau methods we show the temperature behaviour of system with competing Heisenberg and Dzyaloshinskii--Moriya interaction (DMI) in contrast with classical Heisenberg system. We show the process of nucleating of skyrmion depending on the value of external magnetic field.

On modeling the martensite nucleation on ferromagnetic clusters

Introduction . The study of the austenite magnetic state in steels has provided the mechanism of the external magnetic field impact on steel under the hardening process. Previous studies have established a positive practical effect of heat treatment in a magnetic field. The work objectives were to create a computer model of the magnetic state of carbon steel austenite; to conduct computational experiments with a system of spins at various values of temperature and external magnetic field. Materials and Methods . The positions of the Ising model were used. The canonical ensemble of spins was modeled by the Monte Carlo method using the Metropolis algorithm. Results . The algorithm was implemented with the initial parameters selected through experimental data on the magnetic state of austenite. The inhomogeneity of this state without exposure to a magnetic field was studied. Data on the sizes of ferromagnetic clusters in austenite at various temperatures were obtained. It has been noted that the presence of an external magnetic field counteracts the temperature disordering of spins. Data on an increase in the size of ferromagnetic clusters under growing magnetic field strength were obtained. Discussion and Conclusions . A two-dimensional computer model of the spin state of austenite of carbon steel has been developed. The computational experiments with various parameters of the model have shown that there is a short-range order in the arrangement of spins above the Curie temperature. With a rise of the temperature of the system, the sizes of ordered regions decrease; but when an external magnetic field is applied, they increase.

Particle-in-Cell Investigation on the Effective Way of Improving the Emission Performance of a Novel Multipacting Cathode

The influences of parameters on the emission performance of a novel multipacting cathode are numerically investigated by using particle-in-cell (PIC) method in this article, including cathode length, material secondary electron yield (SEY), and the magnitude values of external magnetic field, applied axial and radial electric field. The numerical results demonstrate that the effective way of improving the emission performance of the novel multipacting cathode is synchronously increasing the magnitude values of applied axial electric field, radial electric field, and external magnetic field. Through this way, the output current could be notably increased. Meanwhile, the output electrons are with low energy spread and good emittance.

Microwave Tunable Devices on the YIG-VO2 structures

The theory describing a tunability of the spin-wave spectrum for the ferrite/vanadium dioxide layered structures through changing the VO2 conductivity is suggested. An influence of the various parameters on the spin-wave wavenumber variations and damping decrement is studied. We show that an effective wavenumber variation with minimal losses is achieved by matching the thicknesses of the ferrite and vanadium dioxide films, as well as the value of external magnetic field. We show also that owing to the electrodynamic interaction, a quality of contact between the ferrite and vanadium dioxide layers is not critical.

THE MODEL OF GAS DISCHARGE SUSTAINED BY THE QUADRUPOLE ELECTROMAGNETIC WAVE IN WAVEGUIDE STRUCTURE WITH VARYING RADIUS OF METAL ENCLOSURE

This article presents the results of the theoretical study of stationary state of gas discharge sustained by the electromagnetic wave with azimuth wavenumber m = −2 in three component magnetized plasma-metal waveguide structure of slightly varying radius of metal enclosure in the framework of electromagnetic model. It was studied the influence of the external magnetic field value, the electron effective collision frequency and other parameters on the phase characteristics, spatial attenuation, discharge stability and axial plasma density profile in the structure with constant radius of metal waveguide and with radius that varies slightly along the discharge.