Magnetic Field Angle Research Articles

Thermosolutal Marangoni convection on a permeable flat surface with aligned magnetic field and thermophoretic effect: an OHAM solution

In this venture, the challenge to study the mathematical model and its approximate solution for boundary layer thermosolutal Marangoni convection on a permeable flat surface with thermophoretic velocity and aligned magnetic field has been undertaken. Using a special type of transformation, governing PDEs are converted into ODEs. A semi-analytical method known as optimal homotopy analysis method(OHAM) has been used to develop solutions for proposed mathematical model. The novelty of the study is in the exploration of simultaneous impacts of thermophoretic velocity and inclined magnetic field on flow and heat-mass transport while mass suction/injection is using OHAM. Solutions obtained by OHAM are compared with other published literature and it is revealed that our numerical values are improved by approximately up to 7%. The obtained solutions for various important parameters are displayed in the form of graphs and tables. The study explores the variable behaviors of velocity, temperature, and concentration for growths of Marangoni number, magnetic parameter, and thermophoretic parameter, while there exists mass suction or injection. It reveals that in both cases, i.e. suction and injection cases, velocity grows and temperature and concentration reduce with increasing magnetic parameters and inclination angle of aligned magnetic field and these variations are more prominent in case injection. If the magnetic field is orthogonal to the flat surface, then corresponding Lorentz force produces maximum resistance for the transport phenomenon. The spreading effect of induced surface velocity due to Marangoni convection is observed in the entire boundary layer region in case of mass suction, while for injection case it is witnessed only near the surface. Whereas, for higher value of thermophoretic velocity, the concentration exhibits a reducing trend. For rising values of Marangoni number, wall velocity, Nusselt number, and Sherwood number significantly grow, while magnetic field has contrary impacts.

Fiber-integrated silicon carbide silicon-vacancy-based magnetometer.

Silicon vacancies in silicon carbide have drawn much attention for various types of quantum sensing. However, most previous experiments are realized using confocal scanning systems, which limits their practical applications. In this work, we demonstrate a compact fiber-integrated silicon carbide silicon-vacancy-based magnetometer at room temperature. First, we effectively couple the silicon vacancy in a tiny silicon carbide slice with an optical fiber tip and realize the readout of the spin signal through the fiber at the same time. We then study the optically detected magnetic resonance spectra at different laser and microwave powers, obtaining an optimized magnetic field sensitivity of 12.3 μT/Hz 12. Based on this, the magnetometer is used to measure the strength and polar angle of an external magnetic field. Through these experiments, we have paved the way for fiber-integrated silicon-vacancy-based magnetometer applications in practical environments, such as geophysics and biomedical sensing.

Thermosolutal hydromagnetic mixed convective hybrid nanofluid flow in a wavy walled enclosure

This paper deals with the effects of an inclined magnetic field and hybrid nanoliquid on thermosolutal mixed convection in a partially heated wavy walled enclosure. Two distinct flow features are considered by performing a variant of heating and concentrating locations in both the vertical walls. The upper border is in motion with the same speed in the right direction. The governing Navier–Stokes equations are modeled to describe thermosolutal phenomena. These equations are solved by reconstructing a recently developed compact scheme. Results are displayed in terms of streamlines, isotherms, iso-concentrations, average Nusselt and Sherwood numbers to evoke the thermosolutal phenomena for various physical parameters. Furthermore, the significance of well-defined parameters influencing the fluid rotation and thermosolutal transfer, namely Richardson number (0.1≤Ri≤10), Lewis number (1≤Le≤5), thermal Grashof number (GrT=104), Buoyancy ratio (−1≤N≤1), Hartmann number (0≤Ha≤40), orientation angle of magnetic field (00≤γ≤900) and solid volume fraction (0.0≤ϕhnp≤0.04) of the hybrid nanofluid are performed generously. Results reveal that the heating areas and the angle γ play a vital role in flow topology, thermal and solutal transport inside the wavy enclosure. In addition, thermal and solutal transfer enhancement are noted with increasing values of γ while thermal and solutal transfer reduction are noted with the increasing Hartmann number. We have noticed that for the change in the concentration of Cu-Al2O3/water hybrid nanofluid (ϕhnp) from 1% to 4%, average Nusselt number is enhanced by 7.46% in Case-I and 5.09% in Case-II whereas average Sherwood number is decreased by 2.42% and 1.58% for Case-I and Case-II respectively. It is also concluded that the single nanofluid is more effective than the hybrid nanofluid in the case of thermosolutal transport phenomena.

Multiscale modelling and numerical homogenization of the coupled multiphysical behaviors of high-field high temperature superconducting magnets

Ensuring the safe and stable operation of the high temperature superconducting (HTS) magnet has become a key problem to be solved currently. In this paper, we developed a numerical homogenization scheme to simulate the coupled electromagnetic-thermal-mechanical behaviors of the REBCO (REBa2Cu3Ox, where RE = rare earth) high field magnets. The homogenized T-A formulation is adopted to model the electromagnetics of HTS tapes. The representative volume element (RVE) based on the micromechanics is created to predict the homogenization properties of the magnets. The field dependences of the critical current density of HTS tapes on the magnetic field, magnetic field angle, the temperature and the strain are considered. The effectiveness and efficiency of the proposed numerical scheme have been well validated through comparisons with experimental results. Moreover, the effects of the anisotropic plasticity on the mechanical behaviors of the HTS magnets are also evaluated. Our results show that compared with the Hill’s anisotropic model the commonly used isotropic von Mises plasticity model underestimates the plastic strain in the magnet. Under ultrahigh magnetic field, quench of the magnet is mainly triggered by the strain-induced degradation in the critical current of HTS tapes, which needs special attention in the design of high field magnets.

Magnetic Inclination Evolution of Accreting Neutron Stars in Intermediate/Low-mass X-Ray Binaries

The magnetic inclination angle χ, namely the angle between the spin and magnetic axes of a neutron star, plays a vital role in its observational characteristics. However, there are few systematic investigations of its long-term evolution, especially for accreting NSs in binary systems. Applying the model of Biryukov & Abolmasov and the binary evolution code MESA, we simultaneously simulate the evolution of the accretion rate, spin period, magnetic field, and magnetic inclination angle of accreting NSs in intermediate/low X-ray binaries. We show that the evolution of χ depends not only on the initial parameters of the binary systems, but also on the mass transfer history and the efficiency of pulsar loss. Based on the calculated results we present the characteristic distribution of χ for various types of systems including ultracompact X-ray binaries, binary millisecond pulsars, and ultraluminous X-ray sources, and discuss their possible observational implications.

Aligned magnetohydrodynamic effect on magnetic nanoparticle with different base fluids past a moving inclined plate

This paper deals with the numerical solutions for the aligned MHD free convection laminar boundary layer flow over a moving inclined plate for two magnetic nanofluids, namely Fe3O4-water and Fe3O4-kerosene. It is assumed that the left surface of the plate is in contact with a hot fluid while the cold fluid is on the right surface. The mathematical model has been constructed and based on the Tiwari-Das model, appropriate similarity transformations are used to convert the governing partial differential equations into nonlinear ordinary differential equations and solved numerically using the Keller-Box method. Numerical results for the skin friction coefficient and local Nusselt number were presented whilst the velocity and temperature profiles were illustrated graphically and analyzed. It is found that the velocity increases and temperature decrease with an increase of aligned magnetic field angle parameter, magnetic strength parameter, and Grashof number while the velocity decreases and temperature increase when inclined plate angle parameter and volume fractions of nanoparticles increase. For the convective parameter, both velocity and temperature profile increase when the Biot number increase. Comparisons with previously published studies are performed and excellent agreement is obtained.

CuO–Water MHD Mixed Convection Analysis and Entropy Generation Minimization in Double-Lid–Driven U-Shaped Enclosure with Discrete Heating

Abstract The present study explores magnetic nanoliquid mixed convection in a double lid–driven U-shaped enclosure with discrete heating using the lattice Boltzmann method (LBM) numerical method. The nanoliquid thermal conductivity and viscosity are calculated using the Maxwell and Brinkman models respectively. Nanoliquid magnetohydrodynamics (MHD) and mixed convection are analyzed and entropy generation minimisation has been studied. The presented results for isotherms, stream isolines and entropy generation describe the interaction between the various physical phenomena inherent to the problem including the buoyancy, magnetic and shear forces. The operating parameters’ ranges are: Reynolds number (Re: 1–100), Hartman number (Ha: 0–80), magnetic field inclination (γ: 0°– 90°), nanoparticles volume fraction (ϕ: 0–0.04) and inclination angle (α: 0°– 90°). It was found that the N um and the total entropy generation augment by increasing Re, ϕ: and γ. conversely, an opposite effect was obtained by increasing Ha and α. The optimum magnetic field and cavity inclination angles to maximum heat transfer are γ = 90° and α = 0.

Investigation on thermal effect of bulk high-temperature superconductors under varying external magnetic field

Superconducting bulks applied to high-temperature superconducting (HTS) maglev vehicles are susceptible to magnetic field, resulting in alternating current (AC) losses and heat generation, which affect the stability of the suspension system. Therefore, the thermal effect of superconducting bulk under external magnetic field is worth studying. The paper uses finite element software to establish a 2D electromagnetic-thermal coupling model. The distribution and variation of HTS bulks’ temperature under varying external magnetic field are simulated and analyzed, and the loss and temperature rise of rectangular bulks with different thicknesses are studied. Finally, the effect of increasing the critical current density on the thermal effect of the superconducting bulk is discussed. The results show that the temperature rise of bulk has a positive correlation with the amplitude and frequency of external magnetic field. The maximum temperature is affected by the angle of magnetic field. Under the same external magnetic field, the bulk with smaller thickness produces smaller loss and temperature rise. The research results can provide important references for the operation and furniture design of HTS maglev vehicles.

Study on magnetization dynamics modulated by spin-orbit-torque in a Ni81Fe19/NiO/Ni81Fe19 multilayered wire

As electrical control of magnetization dynamics opens the door to realize spintronic devices, understanding the microscopic mechanisms of spin current transport and its effect through the antiferromagnetic and interface is crucial. We studied magnetization dynamics modulated by the spin current originated from the spin-orbit-torque using the rectifying planar Hall effect (PHE). In Ni81Fe19/NiO/Ni81Fe19 heterostructure wire deposited on Pt/Ta cross-tie electrode, we measured the rectifying PHE as a function of external magnetic field angle and dc electric current. By measuring the electrical responses of the heterostructure system, we found that the magnetization dynamics can be modulated by the dc electric current flowing through the Pt/Ta electrode.

Optimization of wavy trapezoidal porous cavity containing mixture hybrid nanofluid (water/ethylene glycol Go–Al2O3) by response surface method

Increasing thermal performance and preventing heat loss are very important in energy conversion systems, especially for new and complex products that exacerbate this need. Therefore, to solve this challenge, a trapezoidal cavity with a wavy top wall containing water/ethylene glycol GO–Al2O3 nanofluid is simulated using Galerkin finite element method. The effects of physical parameters affecting thermal performance and fluid flow, including porosity (ℇ), thermal radiation (Rd), magnetic field angle (α), Rayleigh number (Ra) and Hartmann number (Ha), are investigated in the determined ratios. The results of applied boundary conditions showed that the optimal values for Ra, Ha, ℇ, Rd and α are 1214.46, 2.86, 0.63, 0.24 and 59.35, respectively. Considering that changes in radiation have little effect on streamlines and isothermal lines. Optimization by RSM and Taguchi integration resulted in optimal Nu detection. It provided a correlation for the average Nu based on the investigated determinants due to the conflicting influence of the study factors, which finally calculated the highest average Nusselt number of 3.07. Therefore, the ideal design, which is the primary goal of this research, increases the thermal performance.

Modeling of magnetized collisional plasma sheath with nonextensive electron distribution and ionization source

The properties of an atmospheric-pressure collisional plasma sheath with nonextensively distributed electrons and hypothetical ionization source terms are studied in this work. The Bohm criterion for the magnetized plasma is extended in the presence of an ion–neutral collisional force and ionization source. The effects of electron nonextensive distribution, ionization frequency, ion–neutral collision, magnetic field angle and ion temperature on the Bohm criterion of the plasma sheath are numerically analyzed. The fluid equations are solved numerically in the plasma–wall transition region using a modified Bohm criterion as the boundary condition. The plasma sheath properties such as charged particle density, floating sheath potential and thickness are thoroughly investigated under different kinds of ion source terms, contributions of collisions, and magnetic fields. The results show that the effect of the ion source term on the properties of atmospheric-pressure collisional plasma sheath is significant. As the ionization frequency increases, the Mach number of the Bohm criterion decreases and the range of possible values narrows. When the ion source is considered, the space charge density increases, the sheath potential drops more rapidly, and the sheath thickness becomes narrower. In addition, ion–neutral collision, magnetic field angle and ion temperature also significantly affect the sheath potential profile and sheath thickness.

Optimization of X-mode electron cyclotron current drive in high-electron-temperature plasma in the EAST tokamak

A discharge with electron temperature up to 14 keV has been achieved in EAST. Analysis of the electron cyclotron current drive (ECCD) efficiency at high electron temperature under EAST parameters is presented using C3PO/LUKE code. Simulation results show that the ECCD efficiency of X-mode increases with central electron temperature up to 10 keV and then starts to decrease above 10 keV, at a specific magnetic field and toroidal angle. The efficiency degradation is due to the presence of the third harmonic extraordinary (X3) downshifted absorption at the low field side (LFS); even the cold resonance of X3 mode is located outside the plasma. As the electron temperature increases from 5 to 20 keV, the X3 absorption increases from 0.9% to 96.4%. The trapping electron effect at the LFS produces a reverse Ohkawa current. The competition between the Fisch–Boozer current drive and the Ohkawa current drive results in a decrease in ECCD efficiency. ECCD efficiency optimization is achieved through two methods. One is to increase the toroidal angle, leading to X2 mode predominating again over X3 mode and the electron resonance domain of X2 mode moving far from the trapped/passing boundary. The second one is to increase the magnetic field to move away the X3 resonance layer from the plasma, hence less EC power absorbed by X3 mode.

Magnetic-field-dependent spin properties of divacancy defects in silicon carbide.

In recent years, spin defects in silicon carbide have become promising platforms for quantum sensing, quantum information processing and quantum networks. It has been shown that their spin coherence times can be dramatically extended with an external axial magnetic field. However, little is known about the effect of magnetic-angle-dependent coherence time, which is an essential complement to defect spin properties. Here, we investigate the optically detected magnetic resonance (ODMR) spectra of divacancy spins in silicon carbide with a magnetic field orientation. The ODMR contrast decreases as the off-axis magnetic field strength increases. We then study the coherence times of divacancy spins in two different samples with magnetic field angles, and both of the coherence times decrease with the angle. The experiments pave the way for all-optical magnetic field sensing and quantum information processing.

Enhancement of magnetoelectric coupling and anisotropy by Galfenol/PZT/Galfenol magnetoelectric sandwich device

In this work, we reported the large magnetoelectric coupling coefficient and magnetoelectric coupling anisotropy in Galfenol/PZT/Galfenol 2-2 symmetric magnetoelectric sandwich devices. The directional solidification method was used to produce a Galfenol alloy with <001> orientation, which possesses a significant magnetostriction of 279 ppm and a piezomagnetic coefficient of 14.8 ppm/Oe. A magnetoelectric coupling laminate of Galfenol/PZT/Galfenol was also prepared. The magnetoelectric coupling coefficient can reach 55.0 V/cm Oe at the resonance frequency under a 0.35 Oe AC excitation magnetic field due to the significant magnetostriction and high piezomagnetic coefficient. Furthermore, there was excellent linearity and sensitivity between the magnetoelectric output voltage and the AC excitation magnetic field. Simultaneously, the device displayed in-plane magnetoelectric anisotropy and cosine variation as the magnetic field angle changed. At its resonance frequency, the device produced a maximum power of 1.4 mW. Finally, the device was shown to power 42 LEDs and a temperature/humidity sensor, demonstrating that the device withGalfenol/PZT/Galfenol sandwich structure has potential in magnetic field sensing and energy harvesting applications. • The device presented the in-plane anisotropy of ME coupling and cosine variation with the change of magnetic field angle. • The produced maximum power of the device was successfully demonstrated to power 42 LEDs and temperature/humidity sensors at its resonance frequency.

Magnetic Fields and Plasma Motions in a Hybrid Martian Magnetosphere

AbstractThe Martian magnetosphere contains elements of induced and intrinsic origin. To display them one must use different coordinate systems. Although the solar‐electric coordinate system (Mars Solar Electric [MSE]) adequately describes the main features of the induced magnetosphere, it removes/suppresses aspects caused by the crustal magnetic sources while rotating the spacecraft position to the MSE‐coordinate system and averaging over many orbits. On the other hand, to observe effects of the crustal field one should use the solar orbital coordinates (Mars Solar Orbital [MSO]). To find a compromise and keeping in mind that the most probable value of the clock angle of the interplanetary magnetic field (IMF) on the Mars orbit is ∼90° we can consider separately cases with positive and negative By components of the IMF. It is shown that dynamics of ion fluxes in the distant regions of the magnetosphere is mainly controlled by induced features. However, reconnection of the draping IMF with crustal field leads to a twisting of the classical draping configuration. Despite of the very intricate local geometry of the crustal field, the low‐order harmonics of the magnetic field and mainly the dipole component determine the reconnection sites, at least, statistically for many Mars rotations. For different signs of the By component of the IMF these sites occur either in the +Y‐MSO or −Y‐MSO hemispheres. As a result, statistically the magnetosphere of Mars looks like a hybrid magnetosphere formed during the solar wind interaction with the obstacle which simultaneously contains an extended ionosphere and a weak dipole magnetic field.

The Spectral Adomian Decomposition Method for the Solution of MHD Jeffery–Hamel Problem

In this study, the effects of magnetic field on the Jeffery–Hamel problem is studied using a powerful numerical method called the spectral Adomian decomposition method (SADM). The traditional Navier–Stokes equation of fluid mechanics and Maxwell’s electromagnetism governing equations are reduced to nonlinear ordinary differential equations to model the problem. Comparisons with the numerical solutions are made to demonstrate the validity and high accuracy of the present approach. The velocity profile of the inner part of the divergent channel is studied for various values of magnetic field parameter and angle of channel. It was found that an increase in the magnetic field parameter leads to increase in the velocity profile. The results indicated that this technique is more efficient and converges faster than the standard Adomian decomposition method.

THERMO-FLUIDIC CONVECTIVE FLOW STUDY OF HYBRID NANOFLUID IN AN INVERTED T-SHAPED POROUS ENCLOSURE UNDER UNIFORMLY ACTING MAGNETIC FIELD

This research work attempted to analyze the impact of a magnetic field having various inclination angles on the hydrothermal convective flow and heat transport phenomena in an inverted T-shaped porous enclosure saturated with water-based hybrid nanofluid. Firstly, a comparative study for accessing the significance and applicability of the hybrid nanofluid over simple fluid (water) is accomplished at various Rayleigh numbers. Furthermore, the generalized Darcy-Forchheimer-Brinkmann model having magnetic forces is numerically simulated through the penalty finite element approach. The complete study covers the parametric studies in the presence and absence of magnetic field for parameters, including the broad-ranging values of Hartmann number (Ha), inclination angles of magnetic field (&amp;zeta;), Rayleigh number (Ra), porosity (&amp;isin;), and Darcy number (Da). Moreover, results obtained from the parametric studies are graphically demonstrated through the isotherms, streamlines, and the variation of mean Nusselt number plots (Nu&lt;sub&gt;m&lt;/sub&gt;). The results variation suggests that the heat transfer rate is getting more robust with Da, Ra, and &amp;isin;, though the appearance of the magnetic field restricts the fluid flows and heat transport. Additionally, the increasing angle supports the heat transfer process till &amp;zeta; &amp;#61; 30 up to some extent, and further, it deteriorates till &amp;zeta; &amp;#61; 90. Thus, a proper inclination and the magnitude of the magnetic field may be a better choice to control the flow regime and the thermal transport phenomena inside the porous domain.

Effects of rf current and bias-field direction on the transition from linear to nonlinear gyrotropic dynamics in magnetic vortex structures

We present a frequency-domain study of the dynamic behavior of a magnetic vortex core within a single Permalloy disk by means of electrical detection and micromagnetic simulations. When exciting the vortex core dynamics in a nonlinear regime, the lineshape of the rectified dc signal reveals a resonance peak splitting which depends on the excitation amplitude. Using micromagnetic simulations, we show that at high excitation power the peak splitting originates from the nanosecond time scale quasiperiodic switching of the vortex core polarity. Using lock-in detection, the rectified voltage is integrated over a ms time scale, so that the net signal detected between the two resonant peaks for a given range of parameters cancels out. The results are in agreement with the reported effects of the in-plane static field magnitude on the gyration dynamics, and complement them by detailed analysis of the effects of the rf current amplitude and the azimuthal angle of the in-plane bias magnetic field. Systematic characterization shows that a transition from linear to nonlinear dynamical regime can be controlled by rf current as well as by varying the magnitude and the direction of the bias magnetic field.

Measurement technique of magnetic anisotropy field on patterned magnetic structures

We propose an electric measurement technique for the magnetic anisotropy field of ferromagnetic thin films and their tiny patterned structures, particularly, in the case of in-plane magnetic anisotropy. This technique measures the anomalous Hall resistance by sweeping the angle or strength of the external magnetic field. The magnetic anisotropy field can be determined explicitly from the linear dependence of the Hall resistance on the angle and strength of the external magnetic field. The present technique can be applied to both ferromagnetic thin films and their patterned magnetic structures with small volumes, overcoming the signal resolution limit of conventional techniques.

Entropy Generation Due to Magneto-Convection of a Hybrid Nanofluid in the Presence of a Wavy Conducting Wall

The two-dimensional, time-independent conjugate natural convection flow and entropy generation are numerically investigated in three different cases of a wavy conducting solid block attached to the left wall of a square cavity. A hybrid nanofluid with titania (TiO2) and copper (Cu) nanoparticles and base fluid water in the fluid part is considered in the presence of a uniform inclined magnetic field. The leftmost wall of the cavity is the hot one and the rightmost one is the cold one. Radial-basis-function-based finite difference (RBF-FD) is performed on an appropriate designed grid distribution. Numerical results in view of streamlines and isotherms, as well as average Nusselt number in an interface and total entropy generation are presented. The related parameters such as Hartmann number, Rayleigh number, conductivity ratio, amplitude in wavy wall, number of waviness, and inclination angle of magnetic field are observed. Convective heat transfer in the fluid part is an increasing function of kr,Ra,γ, while it deflates with the rise in Ha in each case. Total entropy generation increases with the increase in Ra and kr but it decreases with Ha values. Average Bejan number ascends with the rise in Ha and descends with the rise in Ra.