Magnetic Wires Research Articles

Magnon-cooparons in magnet-superconductor hybrids

Generation and detection of spinful Cooper pairs in conventional superconductors has been intensely pursued by designing increasingly complex magnet-superconductor hybrids. Here, we demonstrate theoretically that magnons with nonzero wavenumbers universally induce a cloud of spinful triplet Cooper pairs around them in an adjacent conventional superconductor. The resulting composite quasiparticle, termed magnon-cooparon, consists of a spin flip in the magnet screened by a cloud of the spinful superfluid condensate. Thus, it inherits a large effective mass, which can be measured experimentally. Furthermore, we demonstrate that two magnetic wires deposited on a superconductor serve as a controllable magnonic directional coupler mediated by the nonlocal and composite nature of magnon-cooparons. Our analysis predicts a quasiparticle that enables generation, control, and use of spinful triplet Cooper pairs in the simplest magnet-superconductor heterostructures.

Wire gauge analysis of planar spiral coil and its optimization technique in Wireless Power Transfer system

Planar spiral coil made of solid wire is widely used in wireless power transfer without magnetic core in high frequency operation system. Based on the magnetic field distribution of planar spiral coil and high frequency eddy current loss mechanism, the influence of magnetic field strength, frequency, and wire gauge on the AC resistance of winding are analysed. It reveals that the coil loss can be reduced by designing the wire gauge. Then the magnetic field strength and the winding loss calculation model are built, based on which the double wire gauge for segmental winding structure is proposed. This method can reduce the AC resistance and improve the quality factor on the premise of keeping inductance constant at high frequency. Through simulation and experiment, the AC resistance of coil based on the double wire gauge scheme can be greatly reduced comparing to the traditional method and the efficiency of the prototype is increased by 4%, which verifies the theory analysis to be correct and flexible.

Correlation between interlayer exchange coupling and domain wall velocity in multilayered magnetic wires

The effect of interlayer exchange coupling (IEC) in {Tb/Co}4/Rh/{Co/Tb}4/Pt multilayered wires on the domain wall (DW) structure and DW velocity was investigated. It was found that the stability of the Néel-type DWs was enhanced and the velocity of the current-induced DW movement increased with an increase in the antiferromagnetic IEC strength. The micromagnetic simulation based on the Landau–Lifshitz equation clarifies that the direction of the magnetic moment in the DWs depends on the antiferromagnetic IEC strength, and the stability of the Néel-type DW increases with an increase in the antiferromagnetic IEC strength. As a consequence of this stability, the spin-orbital torque affects effectively on the magnetic moment of the DWs and the DW velocity increases. These results imply that the DW velocity in magnetic domain-based memories can be controlled by the antiferromagnetic IEC strength.

Origin of helicity-dependent photoconductivity in magnetic and nonmagnetic wires

We study the opto-electric response in metallic wire structures. The aim is to understand the origin of helicity-dependent photoconductivity. For nonmagnetic metals this effect is generally believed to probe spin polarization. Using magnetic wires we show that this method enables background free imaging of spin textures. Analyzing the physical origin we find that the circular dichroism slightly modulates the absorption. The corresponding thermal modulation explains the measured electrical signals. We apply this result to examine the spin Hall effect induced spin accumulation in heavy metals. Here, we show that previously reported results in nonmagnetic wires are well reproducible, but not related to the spin polarization.

Magnetic binary encoding system based on 3D printing and GMI detection prototype

In this work, the feasibility of a magnetic binary encoding system using 3D printing technology is analyzed. The study has a double interest, that is, the possibility of printing a 3D piece that contains the codified information and the development of a system for its decoding. For this purpose, magnetic nanoparticles (magnetite Fe 3 O 4 ) were embedded in a polymeric matrix of Polylactic Acid (PLA) and Poly-ε-caprolactone (PCL). Similar to a conventional barcode, a rectangular piece with an alternating pattern of strips with absence (only polymer) and a 5 wt% of embedded magnetic nanoparticles was 3D printed employing the Fused Deposition Modelling technique (FDM). The information was decoded by means of a Giant Magnetoimpedance (GMI) sensor-based prototype, by scanning the surface of the piece and measuring the changes in the magnetic field. As sensor nucleus, an amorphous soft magnetic wire of nominal composition (Co 0.94 Fe 0.06 ) 72.5 Si 12.5 B 15 was employed. The decoding prototype incorporates a homemade electronic sensor interface that permits, at the time, the GMI sensor excitation and the subsequent signal conditioning to optimize its response. The output signal enables the detection of the magnetite nanoparticles and the magnetic decoding of the encoded information (“1” and “0”, presence or absence of the magnetic nanoparticles, respectively). • Fabrication of 3D printable filaments with embedded magnetic nanoparticles (Fe 3 O 4 ). • 3D printing of a functional piece with encoded information (barcode). • Decoding of hidden (no visible) codes using low-cost GMI-based decoder.

Removal of Magnetic Fine Particles From Carbon Black Powder by High Gradient Magnetic Separation Under Dry Condition

Removal of magnetic fine particles from carbon-black powder by utilizing the high gradient magnetic separation with a newly developed magnetic wire filter under dry condition was studied. The developed magnetic filtering system has magnetic thin wires arranged in one direction with a regular interval and the rotating layered structure perpendicular to the magnetic field direction. This makes it possible to capture the magnetic fine particles without clogging the filter under dry condition. The capture rate in the magnetic filter was investigated in detail by both magnetic separation experiments and three-dimensional FEM particle trajectory simulations. With reducing both the magnetic wire size and the wire spacing, and with increasing the number of layers, the capture rate increased significantly. By optimizing the filter design, we succeeded in removing 100% of iron particles with a size of 48 microns in carbon black powder under low magnetic fields without clogging the filter. Consequently, it became clear that the newly developed filter is very effective in removing magnetic particles in the powder under dry condition.

Evaluation of multi-bit domain wall motion by low current density to obtain ultrafast data rate in a compensated ferrimagnetic wire

Architectures based on multi-bit magnetic domain walls (DWs) take advantage of the fast speed, high density, nonvolatility, and flexible design of DWs to process and store data bits. However, controlling multi-bit DWs driven by electric current at an ideal position remains a significant challenge for developing integrated spintronic applications with high reliability and low power consumption. We exhibit the possibility of driving fast and stable multi-bit DWs at low current density without an in-plane external magnetic field in Fe-rich GdFeCo magnetic wires. When an in-plane magnetic field is applied in the wire direction, the front edge accelerates, although the rear edge decelerates, and the recorded data are destroyed. Hence, this method is not practical. Here, the DW speed of the multi-bit DWs is 1500 m/s under a low current density of 29 × 1010 (A/m2). A straight DW shape is required to accurately read the bits of information by the tunneling magnetoresistance head in real DW memory devices. Moreover, we demonstrate that the DW position is related to the DW shape after injecting a pulse current into the magnetic wire. A straight DW shape is exhibited for 3 ns pulse duration width, while the DW shape became rounded for 30 and 50 ns pulse duration widths. Our finding provides a practical concept for multiple-bit-per-cell memory and presents a viable platform for DW memory applications.

The effect of substrate surface integrity on the surface properties of TiCrN coating applied via the CAE‐PVD method

AbstractThis study aims to investigate how the predeposition machining processes such as magnetic grinding, turning machining, and wire electrical discharge machining can influence the surface properties including electrochemical and tribological behavior of TiCrN nanostructured coating applied on Mo40 steel substrate. A physical vapor deposition technique using cathodic arc evaporation was used to apply the coating. The crystallographic phases and the microstructure of the coating were studied by X‐ray diffraction and scanning electron microscope, respectively. Rockwell‐C, electrochemical impedance spectroscopy and potentiodynamic polarization, and pin‐on‐disk wear tests were employed to evaluate the adhesion strength, corrosion behavior, and tribological property of specimens, respectively. The electrochemical results after 24 h of exposure to 3.5 wt% NaCl solution showed that TiCrN coating pretreated with a turning process with polarization resistance of about 3525.32 Ω.cm2 had the best corrosion resistance among all specimens. This was because of the improvement of the smoothness, surface quality, and adhesion after the turning process. On the other, the friction coefficient of the grounded sample is less than that of other ones. This is probably due to its higher adhesion strength and higher surface smoothness.

Estimation of a surface magnetization direction of thin cylinders by magnetooptical Kerr effect

Magneto-optical Kerr effect (MOKE) imaging is a versatile technique for probing a surface magnetization of magnetic materials. Here, we investigate the influence of the polarizers' rotation on the resulting magnetooptical contrast of thin magnetic wires with cylindrical geometry. Employing MOKE microscopy, we image the magnetooptical contrast change and quantify the contribution of the spatially curved cylindrical surface to the overall magnetic contrast. The calculated magnetooptical contrast difference for various extinction angles between polarizer and analyzer provide an estimation of the surface magnetization orientation at curved surfaces. The magnetooptical analysis scheme can be extended to other non-planar magnetic surfaces.

Effects of the wire mesh on pulsed eddy current detection of corrosion under insulation

ABSTRACT Pulsed eddy current (PEC) technique has been used to detect corrosion under insulation (CUI) for decades, but whether and how the wire mesh laid in the insulation layer affects the detection remains ambiguous. This paper touches on this issue for the first time. The insulated structure was simplified to a carbon steel plate covered by a cladding with an air gap representing the insulation layer, in which the wire mesh was situated. Finite element simulations were performed on the simplified model and found that the aluminium or stainless steel wire mesh had little effect on eddy currents in the plate, while the mild steel wire mesh could cause a considerable increase in the probe footprint and a significant drop of the eddy current density. For the mild steel wire mesh, the magnetic permeability and wire diameter were the main factors affecting the probe footprint and eddy current density. Afterwards, simulations were conducted to analyse the effect of the mild steel wire mesh on the PEC probe performances for evaluating the CUI depth and found that the mild steel wire mesh led to decreases in both the PEC signal amplitude and decay rate. The simulation results were finally verified by experiments.

Simulation and Modeling of Racetrack Memories With VCMA Synchronization

The control of the motion of magnetic domains is of crucial interest for the development of several spintronic applications, such as high-density racetrack memories and domain wall logic. In these devices, domain wall manipulation can be achieved via pulsed currents or applying external fields. However, real-world applications require accurate signal synchronization systems, keeping limited the power budget. Up to now, geometrical restrictions in the magnetic wire, known as notches, were used to confine domain walls at the expense of high resolution of the fabrication process. The solution based on the Voltage-Controlled Magnetic Anisotropy (VCMA) effect appears more promising—it is successful for controlling the skyrmion motion—avoids the need for strong depinning currents, simplifies the fabrication process, and gives more freedom in the control logic. The anisotropy variation induced by the VCMA can create barriers or wells that can be used to limit the movement of domain walls and obtain an effective synchronization. In this article, we propose a system-level evaluation of the effectiveness of the proposed VCMA synchronization method. Starting from a two-coordinates model, the motion of domain walls, the performance, and the efficiency of the approach are evaluated. We modeled the delay using SPICE. The VCMA showed clear advantages in the realization of the confinement structure at the system level with respect to the notch solution.

Control of the Walker breakdown by periodical magnetic wire-width modulation

Suppression of the Walker breakdown in confined wires is key to improving the operation and reliability of magnetic domain-wall-based devices, including logic, memory, and sensor applications. Here, via micromagnetic simulations, we demonstrate that periodical wire-width modulation with suitable geometric parameters can fully suppress the Walker breakdown of a field-driven domain wall, conserving its spin structure in the whole operating field range of a device. Key differences in the efficacy of the wire-width modulation are observed for wires with different widths and thicknesses such that different domain wall states are energetically stable. In particular, the approach is found to be effective in expanding the field-operating window of a device in the case of smaller wire widths and thicknesses (below 150 nm wide and 15 nm thick), whereas in larger wires, the advantages from the suppression in the Walker breakdown are counteracted by the increase in domain wall pinning and the reduction in the nucleation field for new domain walls. Simulations on intersecting magnetic wires prove the importance of suppression of the Walker breakdown. Since the domain wall behavior is chirality dependent, introducing periodical wire-width modulation conserves the spin structure, thus reducing stochasticity of the domain wall propagation.

Magnetic Resonance Wire Coil Losses Estimation with Finite-Difference Time-Domain Method

Radiofrequency (RF) coils are used to transmit and receive signals in magnetic resonance (MR) systems. Optimized RF coil design has to take into account strategies to maximize the coil performance by choosing coil sizes and geometry for achieving the best signal-to-noise ratio (SNR). In particular, coil conductor and radiative loss contributions strongly affect the SNR value, with the first mainly playing a role in low-field MR systems especially, while the second could be the dominant coil loss mechanism for high-frequency tuned coils. This paper investigates the accuracy of the finite-difference time-domain (FDTD) method for separately estimating coil conductor and radiative loss contributions. Comparison with finite element method (FEM) analysis and workbench measurements performed on a home-built coil prototype permitted us to validate the simulation results. Moreover, this research, jointly with literature data on sample-induced losses estimation, demonstrates that an FDTD-based solver permits providing an SNR model for coils with various and complicated geometries.

Direct Writing of Shape‐Gradient Magnetic Alloy Microwire Arrays with Meniscus‐Confined Electrodeposition Process

AbstractGradient magnetic micro/nanowire arrays have attracted widespread attention due to their interesting properties. However, fabricating such an ordered array of gradient micro/nanowires with controllable diameters and compositions is still a great challenge to most of the current methods. Here, meniscus‐confined electrodeposition (MCED) technique is adopted for the rapid prototyping of the shape‐gradient magnetic Cu/Co‐alloy microwire arrays by adjusting the printing speed continuously, which provides a novel idea for the preparation and performance research of shape‐gradient magnetic alloy microwire arrays with well‐defined structures. It is found that the key to fabricating controllable gradient alloy micro/nano structures by increasing the printing speed is to continuously stretch the meniscus within the stable range of the meniscus. In the range of incremental speed in this study, the shape‐gradient magnetic alloy wires with stable and uniform compositions and dense internal structures can be successfully prepared, and the gradient ratio can be adjusted from 0 to about 0.025. Compared with the uniform‐diameter array, the shape‐gradient magnetic alloy array shows an improvement in remanence and coercive force.

The Research of 30 mm Detecting Distance of Testing Device for Wire Rope Based on Open Magnetizer

Wire rope will have defects such as local faults (LF) and loss of metal area (LMA) during the long-term using process. The nondestructive testing method of magnetic flux leakage (MFL) has been widely used in wire rope defect detection. Currently, the detecting distance between magnetic sensors and wire rope with the MFL method is relatively small (2–5 mm). Considering the inner surface of the sensor head is close to the wire rope, it quickly leads to the sensor head scraping off the surface oil of the wire rope or being stuck by a cut wire in the course of MFL detection. Therefore, it is challenging to realize the sensor with MFL detection of wire rope obtaining the weak signal at a large lift-off (>30 mm). This study used finite element analysis to verify if the MFL signal exists at the large lift-off (>30 mm). Meanwhile, the sensor head was improved using an open magnetizer to make the wire rope reach saturation and excite enough magnetic leakage field. By combining magnetic sensing and coupling and a weak analog signal processing method, not only was the signal effectively detected, but also the signal-to-noise ratio (SNR) was improved. Finally, experiments verify the feasibility of detecting defects at a large distance. The method also has been applied in the high-speed detection of wire rope, which can detect broken wire of 1 mm diameter.

Study on magnetic-field-based abrasive grains patterning for electroplating diamond wire saws

In this study, the magnetic field-based abrasive grain patterning for the production of electroplating diamond wire saws was studied. During the manufacturing process of the electroplating diamond wire saw, a permanent magnet was used to perform magnetization of the carbon steel wire. In addition, the following two methods were further used to perform partial degaussing on the carbon steel wire. The first method refers to the laser degaussing method, and the second method refers to the electromagnetic degaussing method, followed by performing electroplating on the carbon steel wire that has undergone the degaussing process. The impacts of these two methods on the magnetization characteristics of the carbon steel wire were studied, the magnetic induction strength of the zone of degaussing, range of the zone of degaussing, production speed, etc., in order to reach a conclusion on the methods for degaussing of a carbon steel wire. In this study, a nanosecond laser with a wavelength of 355 nm was used to perform a partial degaussing treatment on the surface of a magnetized carbon steel wire. When the laser fluence is 11.56 J/cm2, the controlled degaussing region of the abrasive grains could be minimized to 83.8 μm.

Rotating flow characteristics in centrifugal high gradient magnetic separation and its effect on particle capture behavior

Centrifugal high gradient magnetic separation (CHGMS) concentrates weakly magnetic minerals at high selectivity, and the rotating flow in the separating area of the CHGMS separator significantly affects its separation performance. In this work, a simulation model based on finite element method was built up to simulate the rotating flow, and the effects of two most important operating parameters affecting the flow, i.e., matrix rotation speed and feed velocity, on the matrix capture behavior were analyzed through a pilot-scale CHGMS separator in concentrating a fine ilmenite ore. The COMSOL Multiphysics simulation of the rotating flow indicates that the slurry in the separating area forms into a rotating flow as a result of the rotation of matrix, and its flow trace length of unit volume slurry prolongs with increase in the matrix rotation speed and reduces with increase in the feed velocity, thereby affecting the collision probability of matrix to particles. It was found that the slurry velocities on the upstream and downstream of magnetic wire in the matrix are significantly higher than those on the right and left sides. There is a large radial velocity gradient in the separating area, which produces a fluid shearing stress to particles in the slurry, thus improves the loosing state of particles and the capture selectivity of matrix; this velocity gradient increases with increase in the matrix rotation speed and decreases with increase in the feed velocity. The capture experiments of matrix to ilmenite particles indicate that the increased matrix rotation speed has a more significant effect on the capture behavior than that of the feed velocity, and these results are basically consistent with those of simulations. This investigation provides an important reference for the optimum development and application of CHGMS technology.

Structural relaxation in metastable magnetic submicronic wires

Changes triggered by low temperature metastable relaxation annealing in the peculiar magnetic behavior of rapidly solidified submicronic amorphous wires are reported. The overall aim was to understand the effects of the associated stress relief process on magnetization switching and magnetic domain wall propagation in these low dimensional amorphous wires with cylindrical symmetry. The results have shown that, even though the employed relatively low annealing temperatures did not initiate any crystallization, i.e., the amorphous state has been preserved, the consequences in terms of magnetic behavior are significant, with important variations in both magnetic switching field and domain wall velocity values. The observed modifications have been interpreted based on the interplay between the magnetoelastic and magnetostatic anisotropies within the submicronic amorphous wires, as well as on the complex changes in the underlying nonlinear stress distribution generated by the rapid solidification process. The outcomes of this investigation, alongside the general framework for their explanation, have unraveled novel ways of accurately tailoring and controlling the magnetic characteristics of the amorphous submicronic wires for developing new applications in sensors and domain wall logic devices, in which rapid switching and fast domain walls can make an important impact.

A Simplified 2-D Equivalent Model for Magnetic Wire Array

Demagnetization factor and corresponding apparent permeability for multiwire arrays using the 3-D finite element method (FEM) are calculated in this article. The effect of distance between magnetic wires on the demagnetization factor and apparent magnetic permeability is studied for various values of relative magnetic permeability. The simulations are compared with experimental results on arrays up to 91 wires. A novel simplified equivalent 2-D model for wire arrays is presented in this article, as a fast method for calculations. The simplified axisymmetrical model consists of a set of hollow cylinders with equivalent volume. The results of the proposed simplified 2-D model fit very well the full 3-D FEM simulations and experimental results. Two different hexagonal and square arrangements for wires are considered both for the simulations and the measurements.

Stochastic Magnetization Switching in Rapidly Solidified (Co0.94Fe0.06)72.5Si12.5B15 Amorphous Submicronic Wires.

Submicrometric magnetic amorphous wires are good candidates for future development of miniaturized sensors and magnetic logic applications. Here we report the results of an in-depth investigation of magnetization switching in rapidly solidified nearly zero magnetostrictive (Co0.94Fe0.06)72.5Si12.5B15 amorphous samples with diameters of the actual magnetic wires between 300 and 450 nm. All samples were found to be magnetically bistable, displaying characteristic rectangular hysteresis loops. This shows that magnetization reversal occurs through the depinning and subsequent propagation of a magnetic domain wall, whose velocity depends on the applied field and on the sample dimensions. The results of this study reveal stochastic nonlinear dependencies of both the magnetic switching field and the domain wall velocity on the sample diameter. The analysis of the potential causes, which include nonlinear residual stresses, fluctuations in wire dimensions (metal and glass), and competing magnetic anisotropies of different origins, show that a combination of all three factors could lead to the observed stochastic behavior. Calculated values of the switching field, which consider only changes in the wire dimensions, indicate that such influence alone cannot account for the strong nonlinearities. The results are important for the applications of such ultrathin cylindrical magnetic amorphous wires.