Application Of High Magnetic Field Research Articles

Effects of applying high magnetic field and doping SiO on magnetoresistance and magnetic properties of evaporated Co thin films

Application of high magnetic field (HMF) during the film growth and dopant of SiO are used to affect nanostructure of the evaporated Co films with a thickness of about 30nm. Then, the relationship of magnetoresistance (MR) and magnetic properties with the nanostructure is explored. The results indicate that columnar growth of the Co film become growth of nanoparticles by doping SiO. HMF and SiO could be used to tune the surface particle size and surface morphology. The SiO suppresses the abnormal aggregation of the Co particle on the surface. The HMF accelerates the Co aggregation on the surface of the Co-SiO films. However, both HMF and SiO have no effect on the hcp phase formation of the films. The variations of these nanostructures significantly affect the MR and magnetic properties. The SiO and the HMF make magnetic isotropy of the Co films become anisotropy. Meanwhile, the coercivity increases 95%. However, the SiO dopant decreases the saturation magnetization. The nanoparticle growth makes the Co-SiO films exhibit a special MR phenomenon that the single MR peak becomes several peaks. These results indicate that the combination of the HMF and SiO dopant provides a new method to affect magnetic properties.

Simulations of Bending and Twisting Mechanical Characteristics of a Cable Strand Made of REBCO Conductors at Cryogenic Temperatures

High-temperature superconducting (HTS) materials, especially REBCO coated conductors (CCs), are promising for the application of high field magnets, current leads, and power devices. However, the current capacity is limited for a single CC. In recent years, several prototypes of cable, conductor, and strand were proposed and demonstrated in order to increase current capacity. Except for the high current capacity, the mechanical property is other one of the important factors in practical applications. This paper numerically analyzed the mechanical characteristics of a quasi-isotropic strand composed of four substrands by stacking ReBCO CCs in parallel, which mainly include dependencies of bending radii and twisting pitches on critical currents. The strain distributions of the strand in bending and twisting as well as combination of bending with twisting were calculated by the simulation method. The results are useful in application of high field and large-scale magnet and current lead in low temperature.

Comparison of Ta3wt%W and Pure Ta as a Wire Reinforcement Element in a Multifilament Composite

In very high field magnetic applications, the windings can see very high Lorentz forces. One way to support a reacted Nb3 Sn wire under high loads is to reinforce the conductor with a high strength, high modulus element in the composite. This has been done previously with pure Ta as well as Cu-Nb multifilament elements. This work compares the results of using Ta3wt%W with pure Ta or pure Cu to reinforce a Cu-Nb multifilament conductor meant to mimic the processing of a Nb3 Sn internal tin type composite. Ta3wt% W is found to provide higher strength than pure Ta to the composite and be compatible with drawing to small diameters. A Ta3wt% W core element was successfully drawn with the Cu-Nb assembly to a diameter of 120 μm. The addition of tungsten to the tantalum also improves the microstructure of the tantalum and results in less interface distortion during processing. The mechanical properties and hardness of the individual elements were monitored during the wire processing to look at work hardening rates. A 2.7% area core made of Ta3wt%W provided more than 10% increase in the mechanical strength of the wire over a copper core and provided twice the strength increase of the same size pure tantalum core.

Critical Current Characterization of Commercial REBCO Coated Conductors at 4.2 and 77 K

Superconducting magnets with magnetic fields of approximately 20 T will be needed for future high-energy accelerators, such as the future circular collider at CERN and/or the Muon Collider in the United States. Such field strengths exceed the levels achievable using low-temperature superconductors, such as Nb 3 Sn or Nb 3 Al. Only high-temperature superconductors can currently achieve such high field strengths. However, there has been a little research published on the electrical transport properties of REBCO coated conductors in high-field low-temperature magnet applications. Thus, we have started the critical current characterization of commercially available REBCO-coated conductors in fields of up to 18 T at 4.2 K. This paper reports some of the critical current measurement results at 4.2 and 77 K for conductors from four different manufacturers: Fujikura Ltd.; SuNAM Co. Ltd.; SuperOx Japan LLC; and SuperPower Inc.

Influence of High Magnetic Field and Zn Doping on Robust CO Phase of La0.5Ca0.5MnO3

Magnetic and electrical transport properties of La0.5Ca0.5−x Zn x MnO3 (x = 0, 0.1, 0.15) have been investigated in a wide magnetic field range from 0 T to 50 T. Experimental results show that doping of nonmagnetic Zn2+ ion at Ca site and application of high magnetic field had obvious tuning effects on the stability of the robust charge-order phase, inducing new magnetization and electrical transport behaviors. In particular, obvious temperature and field hysteresis was induced, leading to enhanced magnetoresistance at around room temperature. Based on the intricate interplay between the external magnetic field and chemical strain (lattice distortion) induced by the dopant, which changed the bond length and the angle of double exchange and partially destroyed the charge-order phase, a weak ferromagnetic phase formed. The hysteretic behavior and enhanced magnetoresistance can be understood based on the tuning effects of the high magnetic field and dopant on the stability of the charge-order phase.

Structure and thermoelectric properties of Al-doped ZnO films prepared by thermal oxidization under high magnetic field

This paper studies the effects of high magnetic field (HMF) on the structure, optical and thermoelectric properties of the doped ZnO thin films. The results show that both Al dopant and application of HMF can affect the crystal structure, surface morphology, elemental distribution and so on. The particles of the thin films become small and regular by doping Al. The ZnO films oxidized from the Au/Zn bilayer have needle structure. The ZnO films oxidized from the Au/Zn-Al bilayer transform to spherical from hexagonal due to the application of HMF. The transmittance decreases with doping Al because of the opaque of Al element and decreases with the application of HMF due to the dense structure obtained under HMF. Electrical resistivity (ρ) of the ZnO films without Al decreases with increasing measurement temperature (T) and is about 1.5 × 10−3 Ω·m at 210 °C. However, the ρ of the Al-doped ZnO films is less than 10−5 Ω·m. The Seebeck coefficient (S) of the films oxidized from the Au/Zn-Al films reduces with increasing T. The S values oxidized under 0 T and 12 T conditions are 2.439 μV/K and −3.415 μV/K at 210 °C, respectively. Power factor reaches the maximum value (3.198 × 10−4 W/m·K2) at 210 °C for the film oxidized under 12 T condition. These results indicate that the Al dopant and the application of HMF can be used to control structure and thermoelectric properties of doped ZnO films.

Electrostatic electron-doping yields superconductivity in LaOBiS2

Electrostatic carrier-doping is attracting serious attention as a meaningful technique for producing interesting electronic states in two-dimensional (2D) layered materials. Ionic-liquid gating can provide the critical carrier density required to induce the metal-insulator transition and superconductivity. However, the physical properties of only a few materials have been controlled by the electrostatic carrier-doping during the past decade. Here, we report an observation of superconductivity in a 2D layered material, LaOBiS2, achieved by the electrostatic electron-doping. The electron doping of LaOBiS2 induced metallic conductivity in the normally insulating LaOBiS2, ultimately led to superconductivity. The superconducting transition temperature, Tc, was 3.6 K, higher than the 2.7 K seen in LaO1-xFxBiS2 with an electron-doped BiS2 layer. A rapid drop in resistance (R) was observed at low temperature, which disappeared with the application of high magnetic fields, implying a superconducting state. This study reveals that electron-doping is an important technique for inducing superconductivity in 2D layered BiS2 materials.

Effect of high magnetic field on structure and magnetic properties of evaporated crystalline and amorphous Fe-Sm thin films

Crystalline and amorphous Fe-Sm thin films have been fabricated by using molecular beam vapor deposition method. Then, the effects of both variation of Sm content and application of high magnetic field during film growth on the structure and magnetic properties of the Fe-Sm films have been explored. The results show that bcc structure of the Fe-Sm films with 5.8% Sm transforms to amorphization with 33.0% Sm. Meanwhile, nanocrystallite is formed in the amorphous Fe-Sm films. However, no Fe-Sm compound exists with the change of Sm content and with the application of high magnetic field. Nevertheless, high magnetic field decreases interplanar spacing. The structural evolution has a significant effect on magnetic properties. Saturation magnetization decreases 290% from 1456emu/cm3 to 373emu/cm3 with the increase of Sm content from 5.8% to 33.0%. The coercivity increases 1225% from 20Oe to 265Oe. Meanwhile, both the saturation magnetization and coercivity of the films decrease with the application of high magnetic field. The reason has been discussed.

A simulation study on the variation of virtual NMR signals by winding, bobbin, spacer error of HTS magnet

Recently, production technique and property of the High-Temperature Superconductor (HTS) tape have been improved. Thus, the study on applying an HTS magnet to the high magnetic field application is rapidly increased. A Nuclear Magnetic Resonance (NMR) spectrometer requires high magnitude and homogeneous of central magnetic field. However, the HTS magnet has fabrication errors because shape of HTS is tape and HTS magnet is manufactured by winding HTS tape to the bobbin. The fabrication errors are winding error, bobbin diameter error, spacer thickness error and so on. The winding error occurs when HTS tape is departed from the arranged position on the bobbin. The bobbin diameter and spacer thickness error occur since the diameter of bobbin and spacer are inaccurate. These errors lead magnitude and homogeneity of central magnetic field to be different from its ideal design. The purpose of this paper is to investigate the effect of winding error, bobbin diameter error and spacer thickness error on the central field and field homogeneity of HTS magnet using the virtual NMR signals in MATLAB simulation.

Superconducting YBa2Cu3O7–δ Nanocomposites Using Preformed ZrO2 Nanocrystals: Growth Mechanisms and Vortex Pinning Properties

Although high temperature superconductors are promising for power applications, the production of low‐cost coated conductors with high current densities—at high magnetic fields—remains challenging. A superior superconducting YBa2Cu3O7–δ nanocomposite is fabricated via chemical solution deposition (CSD) using preformed nanocrystals (NCs). Preformed, colloidally stable ZrO2 NCs are added to the trifluoroacetic acid based precursor solution and the NCs' stability is confirmed up to 50 mol% for at least 2.5 months. These NCs tend to disrupt the epitaxial growth of YBa2Cu3O7–δ, unless a thin seed layer is applied. A 10 mol% ZrO2 NC addition proved to be optimal, yielding a critical current density JC of 5 MA cm−2 at 77 K in self‐field. Importantly, this new approach results in a smaller magnetic field decay of JC(H//c) for the nanocomposite compared to a pristine film. Furthermore, microstructural analysis of the YBa2Cu3O7–δ nanocomposite films reveals that different strain generation mechanisms may occur compared to the spontaneous segregation approach. Yet, the generated nanostrain in the YBa2Cu3O7–δ nanocomposite results in an improvement of the superconducting properties similar to the spontaneous segregation approach. This new approach, using preformed NCs in CSD coatings, can be of great potential for high magnetic field applications.

Stress–Strain Distribution Analysis in Bi2212 Subcable Based on Numerical Modeling and Experiment

There has been sustained interest in the development of the Bi2212/Ag round wire (RW) because of its unique potential for applications in high-field magnets (25 T or higher). The Bi2212 conductor is a round strand, which is a very favorable shape to produce multistage twisted cable-in-conduit conductors (CICCs) for the next fusion machine (DEMO). One drawback of Bi2212 is its fragile mechanical properties. The stress and strain accumulated during cabling, the thermal contraction during cooldown, and the electromagnetic load can have a severe impact on the transport properties of the Bi2212 RW. In order to investigate the strain distribution of Bi2212 in CICC, some research and development work was made at the Institute of Plasma Physics, Chinese Academy of Sciences (ASIPP). A simple cable wound with three Bi2212 RWs was manufactured and subjected to mechanical tests. A numerical model was proposed to analyze the stress-strain distribution of a wire inside a cable at cryogenic temperature. Comparisons were made between the model and experimental results. Based on the results and improved understanding of the mechanical behavior, an optimization could be implemented to reduce the Bi2212 cable degradation, in terms of conductor design, manufacture, and operation.

Dimensional Changes of Nb3Sn Rutherford Cables During Heat Treatment

In high field magnet applications, Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn coils undergo a heat treatment step after winding. During this stage, coils radially expand and longitudinally contract due to the Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn phase change. In order to prevent residual strain from altering superconducting performances, the tooling must provide the adequate space for these dimensional changes. The aim of this paper is to understand the behavior of cable dimensions during heat treatment and to provide estimates of the space to be accommodated in the tooling for coil expansion and contraction. This paper summarizes measurements of dimensional changes on strands, single Rutherford cables, cable stacks, and coils performed between 2013 and 2015. These samples and coils have been performed within a collaboration between CERN and the U.S. LHC Accelerator Research Program to develop Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn quadrupole magnets for the HiLumi LHC. The results are also compared with other high field magnet projects.

Bending Tests of HTS Cable-In-Conduit Conductors for High-Field Magnet Applications

A high-temperature superconducting (HTS) cable-in-conduit conductor (CICC) suitable for high-field magnet applications and comprised of twisted-stacked coated-conductor tapes arranged around a helically slotted core has been recently proposed and tested, demonstrating full compatibility with existing cabling technologies. To form the desired shape of any coils for high-field magnet applications, any suitable CICC option needs to be bent. For a magnet design, it is then very important to characterize the bending behavior of the CICC and, in particular, to find the smallest bending radius achieved without performance degradation. To this aim, bending tests were carried out on 1-m-long dummy samples of five helical slots in an extruded aluminum core, in which four REBCO tapes and dummy stainless-steel tapes were mounted in each slot. A controlled bending moment has been applied to the HTS CICC samples at room temperature, and each individual superconducting tape has been electrically characterized as a function of bending radius by measuring the critical current and n-index values at 77 K in a self-field condition. Results are analyzed and explained with the help of a three-dimensional cable model implemented in ANSYS and analytical calculations. The experimental and numerical results presented in this paper will demonstrate that the twisted-stack slotted-core technology can meet the bending requirements of high-field magnet designs.

Passivation of magnetic material used in cell culture environment

Magnetic materials have been widely used for various electromagnetic actuators. However, there still exists a corrosion problem for most magnetic materials when used in a biological cell environment. The metal ions released can cause cytotoxicity. In this paper, we characterize the corrosion of a soft-magnetic FeCo alloy, which has been adopted in our magnetic tweezers, in several cell culture media. Obvious accelerated corrosion was observed in cardiomyocyte and neuronal cell media, but not in Dulbecco’s Modified Eagle Medium. To eliminate the corrosion we examined electrochemical deposition of polypyrrole as well as pyrolytical deposition of parylene C for passivation. It was found that the quality of polypyrrole deposition was insufficient in the area near the edges of the tweezers tips where they had been laser-cut. However, the parylene C coating exhibited excellent isolation properties. In addition, parylene C-coated magnetic parts can also withstand repeated high magnetic field application. The cell viability of in vitro cultures exposed to the passivated material was inspected by live/dead cell staining. Both cardiomyocyte and primary neuronal cells could be cultured on parylene C coated magnetic parts for up to three weeks.

Study of 2G HTS Superconducting Coils Using Line Front Track Approximation

This paper demonstrates an efficient method to calculate the ac losses in multipancake coils. We use the front track line to analyze stacked pancakes by assuming that the current fronts are straight lines and using the critical state model. The current distribution is solved by minimization of total magnetic energy. The calculated ac loss results are compared with the well-accepted H-formula in COMSOL. We further apply this model to the design of a SMES with 2 kJ, which is under construction. The object of the design is to maximize the stored energy and decrease the ac loss. We discuss the detailed geometry parameters and operation temperature with the validated numerical model. Our model provides a fast calculation method of ac loss in stacked (Re)BCO pancakes and is useful to HTS applications in high field magnets, energy storage devices, and electric machines.

Tuning Superconductivity in FeSe Thin Films via Magnesium Doping

In contrast to its bulk crystal, the FeSe thin film or layer exhibits better superconductivity performance, which recently attracted much interest in its fundamental research as well as in potential applications around the world. In the present work, tuning superconductivity in FeSe thin films was achieved by magnesium-doping technique. Tc is significantly enhanced from 10.7 K in pure FeSe films to 13.4 K in optimized Mg-doped ones, which is approximately 1.5 times higher than that of bulk crystals. This is the first time achieving the enhancement of superconducting transition temperature in FeSe thin films with practical thickness (120 nm) via a simple Mg-doping process. Moreover, these Mg-doped FeSe films are quite stable in atmosphere with Hc2 up to 32.7 T and Tc(zero) up to 12 K, respectively, implying their outstanding potential for practical applications in high magnetic fields. It was found that Mg enters the matrix of FeSe lattice, and does not react with FeSe forming any other secondary phase. Actually, Mg first occupies Fe-vacancies, and then substitutes for some Fe in the FeSe crystal lattices when Fe-vacancies are fully filled. Simultaneously, external Mg-doping introduces sufficient electron doping and induces the variation of electron carrier concentration according to Hall coefficient measurements. This is responsible for the evolution of superconducting performance in FeSe thin films. Our results provide a new strategy to improve the superconductivity of 11 type Fe-based superconductors and will help us to understand the intrinsic mechanism of this unconventional superconducting system.

Size-dependent structure and magnetic properties of co-evaporated Fe-SiO2 nanoparticle composite film under high magnetic field

Composite film of Fe nanoparticles embedded in a SiO2 matrix has been prepared by the co-evaporation of Fe and SiO2. Both source temperature and in-situ high magnetic field (HMF) have been used to adjust the Fe particle size and the growth of Fe-SiO2 film. The size of Fe particle decreased with increasing the source temperature without HMF. When HMF was presented during the growth of the film, the size of Fe particle was enlarged and reduced for source temperatures of 1300 °C and 1400 °C, respectively. Meanwhile, the preferred orientation of the film grown at 1400 °C became uniform with the application of HMF. In addition, it is also found that the film was formed in two layers. One layer is formed by the Fe particle, while the other is free of Fe particles due to the existence of more SiO2. The structural variation has a significant effect on the magnetic properties. The coercivity (90 Oe) of the 1300 °C film is much higher than that (6 Oe) of the 1400 °C film with a small particle size and uniform orientation. The saturation magnetization can be increased by increasing the Fe particle volume fraction. This study develops a new method to tune the soft magnetic properties by the co-evaporation of Fe and SiO2.

Magnetic Ionic Liquid in Magmolecular Process for Uranium Removal

The magmolecular process is a recently proposed environmental friendly technique for treatment of wastewater by utilization of magnetic field. In this work, the application of high magnetic field considered for uranium removal from industrial effluent investigated. Highly magnetic ionic liquid of 1-butyl-3-metylimidazolium tetra chloroferrate was used as the extracting solvent in dispersive liquid–liquid extraction method with regard to the utilization of magnetic field in magmolecular process. For dispersing solvent, acetonitrile was employed. Through experimental design and using the response surface methodology, the effects of specific process variables such as pH, volume of disperser and extracting solvent, concentration and volume of feed on the extraction yield were investigated and the optimal condition of extraction was determined as pH=1.53, feed concentration equal to 33.88ppm, volume of extracting and disperser solvent equal to 0.48 and 4.51mL, respectively, in which the magnetic filtration was applied then. The investigations on the dependency of yield of magnetic filtration step on temperature and magnetic field intensity revealed that an increase in temperature results in reduction in yield, while magnetic field intensity increases yield significantly.

Effect of Magnetic Resonance Applications on Dental Amalgam Phase Changes

Aim: The aim of this study was to examine the potential for low- versus high-field strength magnetic resonance applications to effect phase changes in high-copper dental amalgam as detected by X-ray diffraction (XRD) analysis. Materials and Methods: Disk-shaped samples (5 x 1 mm2) of amalgam filling were prepared (n = 90) and were thermocycled for 1000 cycles. The samples were then divided into three groups that were exposed to a 0.2 tesla or a 1.5 tesla magnetic field, or received no magnetic field exposure as a control. The samples were subsequently examined by XRD for phase determination 1, 7, and 30 days later. Results: The relationships between the gama, gama1, and eta phases, as well as the mercury peak intensities, were statistically analyzed using analysis of variance and the Kruskal Wallis test. No statistically significant differences were observed (p > 0.05). There were also no significant time-dependent differences observed between the gama, gama1, and eta phases, or in the mercury peak intensities, of the groups, according to the Friedman test (p > 0.05). Conclusion: The results of this study indicate that exposure to a magnetic field via magnetic resonance imaging does not affect the structure of dental amalgam. Keywords: Dental amalgam, magnetic resonance imaging, x-ray diffraction.

Intensification of heat transfer with an application of strong magnetic gradients

Experimental analysis of a strong magnetic field influence on heat transfer by paramagnetic fluid was conducted. A rectangular enclosure, filled with working fluid, was placed inside superconducting magnet’s working section in Rayleigh-Benard configuration and three temperature differences between heated and cooled walls ΔT= 3, 5, 11 [°C] were applied. On the basis of performed measurements heat transfer analysis in the form of Nusselt number, conduction and convection heat fluxes calculations was conducted. Obtained results demonstrated that Nusselt number strongly depends on the temperature difference between thermally active walls as well as on the magnetic induction applied to the system. An application of external high magnetic field from 0 [T] to 10 [T] caused an increase of the heat transfer rate – about 250% for ΔT = 3 [°C] and over 340% for ΔT = 5, 11 and 20 [°C] and can be successfully implemented to heat transfer intensification for paramagnetic fluids.