Tilted Magnetic Field Research Articles

Investigation of the effect of torch tilt and external magnetic field on arc during overlapping deposition of wire arc additive manufacturing

PurposeThe purpose of this paper is to find a theoretical reference to adjust the unsymmetrical arc shape and plasma flow of overlapping deposition in wire arc additive manufacturing (WAAM) and ensure the effect of the gas shielding and stable heat and mass transfer in deposition process. The multiphysical numerical simulation and physical experiment are used for validation.Design/methodology/approachIn this study, welding torch tilt deposition and external parallel magnetic field–assisted deposition are presented to adjust the unsymmetrical arc shape and plasma flow of overlapping deposition, and a three-dimensional numerical model is developed to simulate the arc of torch tilt overlapping deposition and external parallel magnetic field–assisted overlapping deposition.FindingsThe comparison of simulated results indicate that the angle of welding torch tilt equal to 20° and the magnetic flux density of external transverse magnetic field equal to 0.001 Tesla are capable of balancing the electric arc and shielding gas effectively, respectively. The arc profiles captured by a high-speed camera match well with simulated results.Originality/valueThese studies of this paper can provide a theoretical basis and reference for the calibration and optimization of WAAM process parameters.

Light absorption in semiconducting quantum dot clusters with fixed surface areas in an external tilted magnetic field

In the present study, we theoretically investigate the far infrared (FIR) spectrum of clusters formed by AlxGa1−xAs/GaAs, GaN/AlN, InSb/GaSb, and ZnSe/CdSe semiconductor hetero-structure quantum dots (QDs). The clusters are obtained by circle packing disc-shaped QDs in a square domain. The close spacing effect has previously been observed by experiment. For a given square area, we analyze the effects of the externally applied magnetic field (intensity and direction) on the FIR absorption coefficient for different QD packing values. The finite difference method is used to solve the two-dimensional Schrödinger equation describing the QD clusters in magnetic fields.

Phase-coherent loops in selectively-grown topological insulator nanoribbons

We succeeded in the fabrication of topological insulator (Bi0.57Sb0.43)2Te3 Hall bars as well as nanoribbons by means of selective-area growth using molecular beam epitaxy. By performing magnetotransport measurements at low temperatures information on the phase-coherence of the electrons is gained by analyzing the weak-antilocalization effect. Furthermore, from measurements on nanoribbons at different magnetic field tilt angles an angular dependence of the phase-coherence length is extracted, which is attributed to transport anisotropy and geometrical factors. For the nanoribbon structures universal conductance fluctuations were observed. By performing a Fourier transform of the fluctuation pattern a series of distinct phase-coherent closed-loop trajectories are identified. The corresponding enclosed areas can be explained in terms of nanoribbon dimensions and phase-coherence length. In addition, from measurements at different magnetic field tilt angles we can deduce that the area enclosed by the loops are predominately oriented parallel to the quintuple layers.

Strong coupling of two quantum dots with a microcavity in the presence of an external and tilted magnetic field

Including an external magnetic field B in a Tavis-Cummings model enable us to consider four exciton states in each quantum dot, two brights and two darks. With a continuous and incoherent pump to a cavity, we explore the conditions of occupation and emission as a function of B. We have found that although the dark excitons are optically inactive, these show a trace of emission as a result of both the strong coupling between light and matter and the interaction between bright and dark exciton states mediated by the magnetic field. Further, tuning one of the quantum dots at resonance with the cavity, we report the set of parameters that allows us to change the resonance condition between exciton states from different quantum dots, namely, we use the magnetic field as a control parameter to select which exciton state and which quantum dot will be mostly coupled to the cavity.

Simulation of nanoliquid thermogravitational convection within a porous chamber imposing magnetic and radiation impacts

Innovative approach for simulation of nanoliquid natural convection through a permeable wavy space was scrutinized. Analysis has been conducted within inclined porous rectangular cavity having cold side borders under the impacts of heated internal wavy horizontal cylinder and uniform tilted magnetic field. The considered boundary-value problem devised on the basis of the Darcy linear law, Boussinesq relation, Rosseland approach and Lorentz force has been resolved by the finite volume technique. The impacts of nanomaterials’ shape, buoyancy force, radiation term and Hartmann number on nanoliquid hydrodynamic treatment have been investigated. Outcomes have proved that greater quantities of shape factor result in the greater convection. By enhancing magnetic forces, convection becomes weaker.

Stabilization of coupled Dzyaloshinskii domain walls in fully compensated synthetic anti-ferromagnets

We examine the combined effects of interlayer exchange coupling (IEC) and the interfacial Dzyaloshinskii-Moriya Interaction (DMI) on the structure of magnetic domain walls in fully compensated synthetic anti-ferromagnets (SAFs). Ir-based SAFs with ferromagnetic (FM) layers based on [Pt/(Co/Ni)M]N were characterized by Lorentz transmission electron microscopy (LTEM). The multi-layer design of the individual ferromagnetic layers enables control of the interfacial Dzyaloshinskii-Moriya interaction (via ‘M’) and, in turn, the structure and chirality of domain walls (DWs). We compare the Fresnel-mode LTEM images in SAF designs with only a change in the purported strength of the DMI. The existence of anti-ferromagnetically coupled Dzyaloshinskii domain walls (DWs) in a high DMI SAF is confirmed through application of in-situ perpendicular magnetic field and sample tilt. This conclusion is based on a unique set of conditions required to observe contrast in Fresnel-mode LTEM, which we outline in this document.

Linear And Nonlinear Intersubband Optical Absorptions In Multiple Quantum Wells Under The External Fields

In this study, the effects of the external fields (electric and tilted magnetic fields) and well parameters on the optical absorption coefficients in GaAs/GaAlAs multiple (five) quantum wells under the applied electric and tilted magnetic fields has been investigated theoretically. Firstly, the energy eigenvalues and eigen functions of an electron confined in multiple quantum wells are calculated by analytically from Schrödinger equation using the transfer matrix method within the effective mass approximation, Secondly, the linear, nonlinear and total intersubband optical absorptions in GaAs/GaAlAs multiple quantum wells system are studied within the compact density-matrix approach. It is shown that the parameters such as strenghts of the external fields and θ-tilted angle values not only shift the peak positions in absorption spectrum but also considerably modify their potential heights. In generally, electronic and optical properties of the quantum wells are very sensitive to the applied external fields and well parameters. Therefore, we can conclude that the effect of the external fields can be used to tune and control the optical properties of interest in the range of the far-infrared electromagnetic spectrum.

Probing and Tuning the Spin Textures of the K and Q Valleys in Few‐Layer MoS2

The strong spin–orbit coupling along with broken inversion symmetry in transition metal dichalcogenides (TMDs) results in spin polarized valleys, which are the origins of many interesting properties such as Ising superconductivity, circular dichroism, valley Hall effect, etc. Herein, it is shown that encapsulating few‐layer MoS2 between hexagonal boron nitride (h‐BN) and gating the electrical contacts by ionic liquid pronounce Shubnikov–de Haas (SdH) oscillations in magnetoresistance. Notably, the SdH oscillations remain unchanged in tilted magnetic fields, demonstrating that the spins of the Q/Q′ valleys are firmly locked to the out‐of‐plane direction; therefore, Zeeman energy is insensitive to the in‐plane magnetic field. Ionic liquid gating induces superconductivity on the surface of unencapsulated MoS2. The spins of Cooper pairs are strongly pinned to the out‐of‐plane direction by the effective Zeeman field, hence are protected from being realigned by an in‐plane magnetic field, namely, Ising protection. As a result, superconductivity persists in an in‐plane magnetic field up to 14 T, in which Tc only decreases by ≈0.3 K from Tc0 as ≈7 K. By applying back gate, the strength of Ising protection can be effectively tuned, where an increase in 70% is observed when back gate changes from +90 to −90 V.

Magnetic properties of GaAs parabolic quantum dot in the presence of donor impurity under the influence of external tilted electric and magnetic fields

The dependence of the magnetization and magnetic susceptibility of donor impurity in parabolic GaAs (Gallium Arsenide) quantum dot has been investigated, at finite temperature under the influence of external tilted electric and magnetic fields. Based on the effective mass approximation, the Hamiltonian of an electron confined in a parabolic quantum dot in the presence of donor impurity which is presented in electric and magnetic fields has been solved by employing the numerical diagonalization method of the Hamiltonian matrix. All the energy matrix elements have been obtained in analytical form. We have shown the variations of the statistical energy and binding energy of donor impurity with the electric and magnetic field strengths and tilt electric field angle. The computed results show that the electrical field can tune the magnetic properties of the QD GaAs medium by flipping the sign of its magnetic susceptibility from diamagnetic (χ < 0) to paramagnetic (χ > 0).

Current-Induced Nucleation and Dynamics of Skyrmions in a Co -based Heusler Alloy

We demonstrate room-temperature stabilization of dipolar magnetic skyrmions with diameters in the range of $100$ nm in a single ultrathin layer of the Heusler alloy Co$_2$FeAl (CFA) under moderate magnetic fields. Current-induced skyrmion dynamics in microwires is studied with a scanning Nitrogen-Vacancy magnetometer operating in the photoluminescence quenching mode. We first demonstrate skyrmion nucleation by spin-orbit torque and show that its efficiency can be significantly improved using tilted magnetic fields, an effect which is not specific to Heusler alloys and could be advantageous for future skyrmion-based devices. We then show that current-induced skyrmion motion remains limited by strong pinning effects, even though CFA is a magnetic material with a low magnetic damping parameter.

Beats of Quantum Oscillations of the Resistance in Two-Subband Electron Systems in Tilted Magnetic Fields

Electron transport in single GaAs quantum wells of widths from 22 to 46 nm with two populated quantum-confinement subbands ES and EAS is investigated at a temperature of T = 4.2 K in tilted magnetic fields B 72° and α > 85°, respectively. The origin of this unexpected behavior of magnetointersubband oscillations in tilted magnetic fields is discussed.

Magnetoabsorption in HgCdTe/CdHgTe Quantum Wells in Tilted Magnetic Fields

Absorption spectra in a 30-nm Hg0.075Cd0.925Te/Cd0.74Hg0.26Te quantum well in tilted magnetic fields up to 13 T have been studied. Energy spectra in the conduction band (in the absence of the normal field component), as well as electron Landau levels spectra in the presence of the magnetic field component in the quantum well plane, have been calculated within the eight-band Kane model. In classical magnetic fields, the broadening of cyclotron resonance lines has been detected; this broadening is due both to the removal of the Kramers degeneracy of the lower quantum-confinement subband and to difference of cyclotron masses in split subbands. The longitudinal field component in quantizing magnetic fields is responsible for the hybridization of Landau levels, which is enhanced with an increase in their energy (on the scale of the quantum confinement energy), manifested in the appearance of “forbidden” transitions in magnetoabsorption spectra.

Piezo-driven sample rotation system with ultra-low electron temperature

Piezo-driven rotator is convenient for tilted magnetic field experiments due to its precise angle control. However, the rotator itself and the sample mounted on it are difficult to be cooled down because of extra heat leaks and presumably bad thermal contacts from the piezo. Here, we report a piezo-driven sample rotation system designed for ultra-low temperature environment. The sample, as well as the rotating sample holder, can be cooled to as low as 25 mK by customized thermal links and thermal contacts. More importantly, the electron temperature in the electrical transport measurements can also be cooled down to 25 mK with the help of home-made filters. To demonstrate the application of our rotation system at ultra-low electron temperature, a measurement revealing tilt-induced localization and delocalization in the second Landau level of two-dimensional electron gas is provided.

Metastable magnetic bubble in [Co/Pd]4/Py multilayers

Magnetic bubbles are topological spin textures that offer interesting physics and great promise for next-generation information storage technologies. The main obstacles so far are that magnetic bubbles are generated with no field stimuli in new material systems at room temperature. Here, we report the observation of individual magnetic bubbles and its high-frequency measurement at room temperature in an exchange-coupled [Co/Pd]4/Py multilayers. We demonstrate that the emergence of magnetic bubbles at remanence can be tuned by the in-plane tilted magnetic field (roughly 3°) along the film plane at room temperature. High frequency results indicate that the presence of magnetic bubbles leads to broadening of the magnetic permeability spectrum lines (due to the non-uniformity of the magnetic moments). Our findings may help to facilitate the application of bubble-based devices at room temperature in exchange-coupled magnetic multilayers.

자기변형모터의 임의의 축에 대한 회전의 실험적 검증

This paper presents an experimental observation of the rotation of a magnetostrictive motor about an arbitrary axis using a Terfenol-D rod and a helical magnetic field. Mangetostrictive motors consist of a solenoidal coil that generates a longitudinal magnetic field, a toroidal coil that generates a circumferential magnetic field, a Terfenol-D rod, a stator, a rotor, and so on. Two experiments were conducted in order to confirm the motors rotation about an arbitrary axis. The first measures the twist angle of the Terfenol-D rod and the second measures the tilt angle of the rotor with respect to the z-axis. The twist angle can be determined by the strain value of the strain gauge attached to the Terfenol-D rod. The tilt angle was obtained using a new trajectory tracking method with five cameras. When the ratio between the circumferential magnetic field and the longitudinal magnetic field changes, the twist and tilt angles also change.

Optical properties of a single quantum well under electric and tilted magnetic fields

In this study, the effects of electric and tilted magnetic fields on changes in the total absorption coefficient and the refractive index, including the linear and third-order nonlinear terms for transition between the ground and first excited level of an electron confined within the GaAs/GaAlAs quantum well, have been investigated. Furthermore, the effects of the magnetic field direction (i.e., different tilt angles) and the well parameters as well as the electric field strength on the optical properties are taken into consideration. The energy levels and wave functions of the system are calculated by using the effective mass approximation and the compact density-matrix approach is used for optical transitions. The obtained results show that the optical properties of the system are sensitive to the applied external fields and well dimensions.

Behavior of fractional quantum Hall states in LLL and 1LL with in-plane magnetic field and Landau level mixing: A numerical investigation**Project supported by the National Natural Science Foundation of China (Grant Nos. 11674041 and 91630205) and Chongqing Research Program for Basic Research and Frontier Technology (Grant No. cstc2017jcyjAX0084).

By exactly solving the effective two-body interaction for a two-dimensional electron system with layer thickness and an in-plane magnetic field, we recently found that the effective interaction can be described by the generalized pseudopotentials (PPs) without the rotational symmetry. With this pseudopotential description, we numerically investigate the behavior of the fractional quantum Hall (FQH) states both in the lowest Landau level (LLL) and first excited Landau level (1LL). The enhancements of the 7/3 FQH state on the 1LL for a small tilted magnetic field are observed when layer thickness is larger than some critical values, while the gap of the 1/3 state in the LLL monotonically reduced with increasing the in-plane field. From the static structure factor calculation, we find that the systems are strongly anisotropic and finally enter into a stripe phase with a large tilting. With considering the Landau level mixing correction on the two-body interaction, we find the strong LL mixing cancels the enhancements of the FQH states in the 1LL.

Detailed Regression Model of Plasma Sheet By

AbstractIn a statistical model plasma sheet By primarily depends on interplanetary magnetic field (IMF) and geodipole tilt τ. With 11 years of Geotail measurements we investigate a role of several other parameters with a linear regression model. Optimal averaging window of IMF input, maximizing correlation and regression coefficients, is found to be 2.25 hr. Influence of IMF and local Bz on IMF penetration (regression with regard to ) and the deviations from the predefined warp deformation are at the level 5–10% relative to the primary model coefficients. The IMF penetration beyond 25 RE is somewhat larger for northward IMF, while closer to the Earth it becomes somewhat larger for southward IMF. These smaller effects turned out to be rather uneven across the tail, making reliable quantification and physical interpretation not always possible. The major reasons of difficulties are uneven coverage and internal correlations in the input space ( –τ– ) due to combination of spacecraft orbit and neutral sheet dynamics, effects of coordinate transformations, etc. In particular, origins of extremely large IMF penetration (order of 30–50% above the average one) for some years and tail locations remain not fully clear. A larger multispacecraft data set covering all seasons in all spatial zones is necessary to further advance in this study.

Experimental determination of Rashba and Dresselhaus parameters and g*-factor anisotropy via Shubnikov-de Haas oscillations

The spin splitting of conduction band electrons in inversion-asymmetric InGaAs/InP quantum wells (QWs) is studied by Shubnikov-de Haas measurements combining the analysis of beating patterns and coincidence measurements in doubly tilted magnetic fields. The method allows us to determine the absolute values of the Rashba and linear Dresselhaus spin–orbit interaction (SOI) coefficients, their relative sign and the full Landé g-tensor. This is achieved by analyzing the anisotropy of the beat node positions with respect to both polar and azimuthal angles between the magnetic field direction and the QW normal. We show that the SOI is dominated by a large Rashba coefficient together with a linear Dresselhaus coefficient that is 10% of the Rashba coefficient. Their relative sign is found to be positive. The g-tensor is found to have a marked out-of-plane anisotropy and a smaller but distinct in-plane anisotropy due to SOI.

Quantum limit in a quasi-one-dimensional conductor in a high tilted magnetic field

Recently, we have suggested Fermi-liquid - non-Fermi-liquid angular crossovers which may exist in quasi-one-dimensional (Q1D)conductors in high tilted magnetic fields [see A.G. Lebed, Phys. Rev. Lett. $\textbf{115}$, 157001 (2015).] All calculations in the Letter, were done by using the quasi-classical Peierls substitution method, whose applicability in high magnetic fields was questionable. Here, we solve a fully quantum mechanical problem and show that the main qualitative conclusions of the above mentioned Letter are correct. In particular, we show that in high magnetic fields, applied along one of the two main crystallographic axis, we have 2D electron spectrum, whereas, for directions of high magnetic fields far from the axes, we have 1D electron spectrum. The later is known to promote non-Fermi-liquid properties. As a result, we expect the existence of Fermi-liquid - non-Fermi-liquid angular crossovers or phase transitions. Electronic parameters of Q1D conductor (Per)$_2$Pt(mnt)$_2$ show that such transitions can appear in feasible high magnetic fields of the order of $H \simeq 20-25 \ T$.