Search

Motivated by the recent experiment done by Yu et al. [X. Z. Yu, et. al., Sci. Adv., 6, 25, eaaz9744 (2020)] on magnetic skyrmion creation and annihilation by electric currents in FeGe devices with a notch structure, we examine the interaction between the electric current vorticity near the notch and localized spins, and obtain three effects of the current vorticity on the localized spins. The first one is an effective Zeeman field induced by the current vorticity. This effective Zeeman field is responsible for skyrmion creation. The second effect is a vorticity-induced Dzyaloshinskii–Moriya (DM) interaction with the direction of the DM vector being parallel to the vorticity direction and is different from the vector of the intrinsic DM interaction. This vorticity-induced DM interaction makes the skyrmions distorted. The third effect is a spin current due to the gradient of the vorticity and the spin current drives the magnetic skyrmions far from the notch. Our theory opens a new path to design the magnetic textures by using structural settings. [ABSTRACT FROM AUTHOR]

Recent theoretical and experimental measurements have underlined the necessity of a theory to calculate the magnetic field created by thermoelectric currents in metals. The main purpose of this article is to help build such a theory. The results are verified by simulations. [ABSTRACT FROM AUTHOR]

In order to couple external circuits to edge-element discretized electromagnetic models, with full field equations, global constraints involving voltages or currents need to be enforced. There is no canonical way to impose a voltage or a current without additional modeling information on the distribution of field sources that rely on topological concepts. In this article, a fast solution of field sources within massive conductors in static and dynamic problems is proposed. Global basis functions, required to cope with non-trivial coil topologies, are directly generated by an iterative solver rather than pre-computing source fields, e.g., by tree–cotree decomposition. [ABSTRACT FROM AUTHOR]

Electromagnetic levitation (EML) melting process is performed by adopting the finite-element method. It is a complicated field-coupled problem, which involves two-way interactions of electromagnetic, thermal, fluid flow fields as well as deformation. Oscillations of a solid titanium metal sample are studied to obtain the time for their balance positions under different electrical factors, such as frequency, current, and the number of coils turn. Droplet size of liquid titanium, which might be affected by different electrical factors, is also studied. It is shown that mathematical model adopted in this paper could be used to dynamically predict the melting process, balance time, and droplets size under the influences different electrical parameters. [ABSTRACT FROM AUTHOR]

Yokeless electric current transducers have compact size, but they are sensitive to external magnetic fields, including those caused by electric currents in their vicinity. It is often believed that this unwanted sensitivity can be effectively suppressed by using a differential sensor. In this paper, we investigate the effect of external current with arbitrary position on busbar differential current sensor. We show the main disadvantage of the differential current sensor: increased sensitivity to currents in the transversal direction, which are not sensed by a single sensor. We analyze by finite element method simulation also the influence of real conductor size and uneven density of ac currents. The results were verified on 1000 A current transducer using a pair of microfluxgate sensors. The realistic suppression of close currents depends on the conductor angular position and in 10 cm distance it can be as low as 50, but it can be corrected if the geometry is known. [ABSTRACT FROM AUTHOR]

Spin torque oscillators placed onto a nonmagnetic heavy metal show synchronized auto-oscillations due to the coupling originating from spin Hall magnetoresistance effect. Here, we study a system having two-spin torque oscillators under the effect of the spin Hall torque, and show that switching the external current direction enables us to control the phase difference of the synchronization between in-phase and antiphase. [ABSTRACT FROM AUTHOR]

This paper presented a passive current sensor in an electric power grid. The sensor consists of an iron–nickel-based ferromagnetic invariant elastic alloy (FIEA) beam with high quality factor ( $Q$ -factor), piezoelectric ceramic Pb(Zr,Ti)O3 (PZT8), and a Permalloy yoke. The beam bends in the magnetic field of a current-carrying wire as a result of the magnetostriction of the FIEA, and the PZT8 produces a voltage proportional to the electric current in the wire. The electric current sensitivity is potentially improved due to the high $Q$ -factor of the FIEA/PZT8 beam and the concentration effect of the Permalloy yoke. Experimental data are taken to evaluate the feasibility of the current sensor. At the power frequency of 50 Hz, the sensor shows the linear sensitivities of 300.5, 177.9, 119.2, and 88.8 mV/A from 0.2 to 5 A when the separating distances are 6, 10, 15, and 20 mm, respectively. The performances indicate that the proposed device is promising for power-frequency current sensing applications. [ABSTRACT FROM PUBLISHER]

We develop a theoretical formula of spin Hall torque in the presence of two ferromagnets. While the direction of the conventional spin Hall torque always points to the in-plane direction, the present system enables to manipulate the torque direction acting on one magnetization by changing the direction of another magnetization. Based on the diffusion equation of the spin accumulation and the Landauer formula, we derive analytical formula of the spin Hall torque. The present model provides a solution to switch a perpendicular ferromagnet deterministically at zero field using the spin Hall effect. [ABSTRACT FROM PUBLISHER]

Electrical bone growth stimulators improve patient outcomes following the spinal fusion surgery, particularly important in high-risk patient populations. The therapeutic electromagnetic field (EMF) effects in tissue were modeled for two Food and Drug Administration (FDA) approved magnetic stimulation devices: 1) Coil A (SpinaLogic, DJO LLC, Vista, CA) and 2) Coil B system (Spinal-Stim, Orthofix Inc., Lewisville, TX). The electric current density induced in the target tissue (spinal vertebra) was compared with that of an FDA approved electric stimulation device (SpinalPak, Biomet, Warsaw, IN). For Coil A and Coil B, the EMF source was current-carrying coils that differed in the design (single coil versus two coaxial coil system) and the current characteristics (continuous 76.6 Hz sinusoid, biased versus intermittent 3850 Hz rectangular pulse bursts repeated at 1.5 Hz, unbiased). The local maximum induced electric field and current density were over 700-fold higher for Coil B system than for Coil A but only half of the values calculated for the reference electric stimulation device. The interaction of the magnetic field and the induced current in the tissue gives rise to local Lorentz force effects expressed as magnetoacoustic pressure (MAP) that for Coil B system reached 5 dB relative to $1~\mu $ Pa of sound pressure level in bone (SPL) (compared with −45 dB for Coil A and absent for capacitive coupling reference device). The analysis broadens the range of possible mechanisms of therapeutic EMF action to include the MAP. [ABSTRACT FROM PUBLISHER]

The paper shows a generalization and further development of a previous work of ours already published. We describe and analyze a kind of devices intended to create a prescribed magnetic field using a set of conductors. More precisely, we discuss a device that is capable of shaping the tangential component of the magnetic field along a specific path by controlling the current applied to each conductor. An orthogonal function decomposition is used to determine the magnitude of each current. The system performance depends on the number of conductors and their location, so we introduce a set of quality parameters, and some common geometries are evaluated upon them. These devices are intended for calibration purposes of current measuring instruments based on Ampere’s integral, although the metrological aspects are out of the scope of this paper. [ABSTRACT FROM AUTHOR]

This paper presents an electric current sensor employing an unsymmetrical magnetoelectric composite Metglas/Pb(Zr,Ti)O3 (PZT) consisting of magnetostrictive Metglas and piezoelectric PZT. As the Metglas foils with excellent magnetic characteristics induce the magnetic field around a current-carrying cable, an output voltage is generated in Metglas/PZT. The influence of the numbers of Metglas foil (L) on resonance output voltage (V \(_{o,\,r}\) ) is experimentally investigated in detail. The results demonstrate that the maximum V \(_{o,\,r}\) is 223 mV for Metglas/PZT with L \(= 4\) under 190.2 Hz frequency and dc biased magnetic field H \(_{\rm dc}= 16\) Oe. By adding a 1.3 g tip mass at the free end of Metglas/PZT, the resonant frequency of Metglas/PZT with L \(= 4\) can be adjusted to 50 Hz, where the V \(_{o,\,r}\) is 211 mV at H \(_{\rm dc} =16\) Oe. With the excellent linearity and large current sensitivity (114.2 mV/A) when measuring low-frequency alternating magnetic fields of 50 Hz, this sensor is ideally suited for power-line current measurement. [ABSTRACT FROM AUTHOR]

In this paper it is shown how to analyze stationary or quasistationary magnetic fields due to arbitrary distributions of electric current in terms of single-valued scalar potentials. The total scalar potential in a specified region outside the magnetic material bodies, not containing electric currents, is obtained by superposing two single-valued Laplacian scalar potentials. One is produced by the given current distribution in an unbounded space and is determined from the free-space values of the normal component of the magnetic field intensity over the region boundary. The other one is defined in the entire region outside the magnetic bodies and is employed in order to satisfy the boundary conditions. When the magnetic bodies can be considered to be linear and homogeneous or piecewise homogeneous, with no electric current within them, the field inside the bodies can also be expressed in terms of Laplacian scalar potentials. If the material of the bodies can be approximated to be ideal ferromagnetic, then the exterior field problem is a Dirichlet problem and is solved independently of the field inside the bodies. The Neumann boundary condition for the interior field problem is provided from the solution of the exterior problem. Differential equation and integral equation formulations, as well as an illustrative application example, are presented. Since the resultant field is computed in terms of only single-valued scalar potentials, the solution techniques based on the formulations presented in this paper are considerably more efficient than those in usual solution methods. [ABSTRACT FROM PUBLISHER]

The present study was designed to explore a novel method of electromagnetic control of cellular activity of aquatic organisms by utilizing a strong magnetic field and weak current stimulation. Three kinds of aquatic organisms, Chlamydomonas pumilio, Daphnia pulex, and Hydra, were exposed to 10 T magnetic fields, and the effects of applying weak electric currents at several milli-amperes on the transmission of polarized light on aquatic organisms at 550 nm was measured. Under ambient fields, the transmission of polarized light was not changed by the electric currents. However, in the presence of a 10 T magnetic field, a strong change in the transmission was observed during and after the electrical stimulation. It was speculated that the cellular components, having both mechanical flexibility and a higher charge density, were affected by the Lorentz force that was generated by the weak electric current and the strong magnetic field. The results indicated that the combination of a 10 T magnetic field and weak stimulation at a mA current level was effective for the measurement and control of the viability of aquatic organisms. [ABSTRACT FROM AUTHOR]

A new class of spin-transfer torque magnetic random access memory (STT-MRAM) is discussed, in which writing is achieved using thermally initiated magnonic current pulses as an alternative to conventional electric current pulses. The magnonic pulses are used to destabilize the magnetic free layer from its initial direction, and are followed immediately by a bipolar electric current exerting conventional spin-transfer torque on the free layer. The combination of thermal and electric currents greatly reduces switching errors, and simultaneously reduces the electric switching current density by more than an order of magnitude as compared to conventional STT-MRAM. The energy efficiency of several possible electro-thermal circuit designs have been analyzed numerically. As compared to STT-MRAM with perpendicular magnetic anisotropy, magnonic STT-MRAM reduces the overall switching energy by almost 80%. Furthermore, the lower electric current density allows the use of thicker tunnel barriers, which should result in higher tunneling magneto-resistance and improved tunnel barrier reliability. The combination of lower power, improved reliability, higher integration density, and larger read margin make magnonic STT-MRAM a promising choice for future non-volatile storage. [ABSTRACT FROM PUBLISHER]

Total electromagnetic force on a body can be predicted by replacing the magnetization and polarization with appropriate equivalent currents and charges. Still, the equivalence of total force does not imply that the integrated densities have physical meaning. Instead of defining local electromagnetic force by using equivalent currents and charges we begin its determination from basic material elements. An example case illustrates how the approach can be used to compute magnetic force densities. [ABSTRACT FROM PUBLISHER]

We investigated spin-polarized current switching of elongated Pac-man (EPM) elements in a Pac-man shaped spin valve (Co/Cu/Py). The aspect ratio, pulse duration, and effect of antiferromagnetic (AFM) layer were simulated to obtain coherent switching. Pulse duration was varied on the picosecond (ps) scale and showed that ultra-fast switching could be achieved. A critical aspect ratio of 4.2 was found, where a minimum current density was observed. For antiparallel to parallel (AP-P) switching, a vortex formed during the switching process for aspect ratios less than 7. Aspect ratios of 7 or higher did not form a vortex and showed similar current densities to parallel to antiparallel (P-AP) switching as a result. It was found that the AFM layer prevented the formation of a vortex at the critical aspect ratio of 4.2 and effectively changed the switching mechanism. This allowed coherent switching with current densities for AP-P and P-AP to be only 7% from each other at the aspect ratio of 4.2. [ABSTRACT FROM AUTHOR]

We have adapted an analytical computer model, RMxprt, to predict the operating parameters of both single-phase and three-phase induction motors as a function of motor lamination material property curves. The model uses newly defined parameters, integrated average core loss (IACL) and integrated average permeability (IAP), rather than the material characteristic commonly used today, 1.5-T permeability, which is not effective in predicting motor efficiency. IACL and IAP have been shown to be excellent predictive parameters of the efficiency of motors, and these parameters are considered the best for specifying motor laminations. IACL is closely correlated with the 1.5-T core loss and IAP is closely correlated with the 1.0-T permeability and, for semiprocessed materials, the 1.5-T core loss. Therefore, the 1.5-T core loss alone can be used to specify semiprocessed cold-rolled motor lamination materials for motors. For all cases studied, directionally averaged IACL and IAP are almost the same as the L&T Epstein pack properties. Therefore, the L&T Epstein pack properties, obtained by conventional Epstein testing, can be used in lieu of the directionally averaged properties. [ABSTRACT FROM AUTHOR]

AC susceptibility and voltage relaxation behaviors after current pulses were studied at various passing through currents for La0.82 Ca0.18 MnO3 single crystals. It was found that a current of 10 mA caused a significant temperature shift towards lower temperatures on the ac-susceptibility versus temperature curve when measured in a cryostat, while the current induced effect was insignificant when the sample is immersed in liquid N2. Exponential decay of voltage was observed after current pulses when measured in the cryostat at 77 K, but the effect was greatly suppressed when measured in liquid N2. The observed results suggest that Joule heating is associated with electrical currents passing through the sample and is the main contribution to the current induced effects. [ABSTRACT FROM AUTHOR]

AC susceptibility and voltage relaxation behaviors after current pulses were studied at various passing through currents for La0.82 Ca0.18 MnO3 single crystals. It was found that a current of 10 mA caused a significant temperature shift towards lower temperatures on the ac-susceptibility versus temperature curve when measured in a cryostat, while the current induced effect was insignificant when the sample is immersed in liquid N2. Exponential decay of voltage was observed after current pulses when measured in the cryostat at 77 K, but the effect was greatly suppressed when measured in liquid N2. The observed results suggest that Joule heating is associated with electrical currents passing through the sample and is the main contribution to the current induced effects. [ABSTRACT FROM AUTHOR]

Statistical treatment of the succession in time of the Barkhausen-noise pulses shows that magnetic noise possesses characteristics that are similar to those of electric shot noise. On the other hand, the electric shot-noise intensity in a noisy component is known to be related directly to the square root of the dc current through the component. Hence, it is intriguing to relate in the same manner the magnetic-noise flux-fluctuations to a magnetic entity similar to the dc current in the electric case. The present work is a successful attempt to demonstrate that such relationship exists. This is attained by employing the duality that relates the time-derivative of the magnetic flux to the electric current. The magnetic noise measurements of commercially available thin-film magnetoresistors confirm the applicability of the proposed approach. The noise was generated by exciting the magnetoresistors by an ac magnetic field along their easy axes. The level of the resulted flux time-derivative was changed by varying the excitation frequency. [ABSTRACT FROM PUBLISHER]