Magnetic Fields Of Several Tesla Research Articles

Oscillations of the Hall Resistivity in Natural Single Crystals of Pyrrhotite Associated with the Orientation of the Elementary Magnetic Moments of Fe Atoms

The Hall resistivity of natural single crystals of pyrrhotite Fe7S8 exhibits oscillations with the inverse external magnetic field 1/B at temperature 77 K and B up to 0.73 Tesla. This resembles phenomena due to Landau quantization of the carriers demanding very pure samples, temperatures near 4 K and magnetic fields of several Tesla. However, none of these requirements is met in the experiments. The oscillations appear only when there is orientation of the elementary magnetic moments of Fe atoms, which happens when B is parallel to the c‐plane at 77 K. At room temperature with the orientation destroyed by the thermal agitation and for B parallel to the c‐axis along which the alignment of the Fe magnetic moments is negligible, the oscillations disappear. According to the s–d model proposed for heavily doped magnetic semiconductors, defects and impurities produce large local fluctuations of carrier concentrations. These through the strong s–d exchange interaction between the carriers and the lattice magnetic moments of Fe establish variations of local magnetization. These constitute scattering centers which are enforced for certain values of B, though for others weaken giving the oscillatory behavior of the Hall resistivity.

Trapped magnetic field and levitation force properties of multi-seeded YBCO superconductors with different seed distance

The performance of large grain (RE)BCO superconducting bulks has the significant potential for magnetic-force based applications such as trapped field magnets and magnetic levitation devices. These materials can trap high magnetic fields of several tesla at temperature below 77 K and also provide stable levitation and high load capacity in magnetic levitation systems. Top seeded melt growth process and multi-seeding technique have been used to enlarge bulk (RE)BCO samples, however many factors affect the growth of multi-seeded bulk (RE)BCO. These include the geometry of sample, the distance between seed crystal, the seed combination and alignment. In this work, we investigated the effects of the distance (d) between two Nd1.8Ba2.4Cu3.4O7 (Nd-123) seed crystals on the characteristics of the (100)//(100) grain junction of top-seeded melt growth (TSMG) processed YBCO bulk superconductors. Four cylindrical shaped Y–Ba–Cu–O samples of dimensions 25 mm in diameter and 7 mm in height with two seed crystals were prepared for this investigation. The fabrication process of these samples is described and their trapped magnetic field and vertical levitation force were measured at 77 K and lower temperatures under Zero-field-cooled (ZFC) and Field-cooled (FC) regimes. We found that both the trapped magnetic field and the vertical levitation force decreased with increasing d value. The trapped field and the vertical levitation force values of the samples with the decreasing the distance between two seed crystals from 16 mm to 1 mm, increased from 0,62 T to 0,78 T and from 13.08 N to 19.41 N, respectively. A peak trapped field value of 4.20 T and vertical levitation force of 19. 41 N has been achieved in this study for YBCO with the distance between two seed crystals of 1 mm. The obtained results can be contributing the properties on improvement of the levitation force and trapped magnetic field and these properties induce widespread usage of multi-seeded YBCO bulks in technological applications.

Interactions of magnetized plasma flows in pulsed-power driven experiments

A supersonic flow of magnetized plasma is produced by the application of a 1 MA-peak, 500 ns current pulse to a cylindrical arrangement of parallel wires, known as an inverse wire array. The plasma flow is produced by the J × B acceleration of the ablated wire material, and a magnetic field of several Tesla is embedded at source by the driving current. This setup has been used for a variety of experiments investigating the interactions of magnetized plasma flows. In experiments designed to investigate magnetic reconnection, the collision of counter-streaming flows, carrying oppositely directed magnetic fields, leads to the formation of a reconnection layer in which we observe ions reaching temperatures much greater than predicted by classical heating mechanisms. The breakup of this layer under the plasmoid instability is dependent on the properties of the inflowing plasma, which can be controlled by the choice of the wire array material. In other experiments, magnetized shocks were formed by placing obstacles in the path of the magnetized plasma flow. The pile-up of magnetic flux in front of a conducting obstacle produces a magnetic precursor acting on upstream electrons at the distance of the ion inertial length. This precursor subsequently develops into a steep density transition via ion-electron fluid decoupling. Obstacles which possess a strong private magnetic field affect the upstream flow over a much greater distance, providing an extended bow shock structure. In the region surrounding the obstacle the magnetic pressure holds off the flow, forming a void of plasma material, analogous to the magnetopause around planetary bodies with self-generated magnetic fields.

Pattern formation in strongly magnetized plasmas: observations from the magnetized dusty plasma experiment (MDPX) device

The last decade has seen the development of new experimental devices to explore the physics of magnetized dusty plasmas. Because of the small charge-to-mass ratio of the charged microparticles, it is necessary to operate these experiments at high magnetic fields of several Tesla in order to observe the direct effect of the magnetic forces on the transport properties of the charged microparticles. While the study of magnetized dusty plasmas is still the ultimate goal, these experiments have also provided new opportunities to studies regimes of strongly magnetized, low temperature, laboratory plasmas that have not been extensively explored. Experiments show the formation of new types of self- and imposed-ordered structures that form in both the plasma and among the microparticles. This paper summarizes recent experimental observations of plasma filamentation (in the plasma) and will discuss possible connections to ‘dust gridding’ phenomena that are observed in the magnetized dusty plasma experiment device.

HTS Bulk Experiments Performed for and Under Space Conditions

In the shadow of dominant long-length high-temperature superconductors bulk HTS show a considerable effort of magnetic engineering application. Bulk HTS are capable of providing easily magnetic fields of several tesla, levitates self- stabilized mirrors or measuring instruments, and can be used as a passive magnetic shield. By simulating space conditions we have been investigated the possible degradation of YBCO material under 160 MeV proton irradiation at a radiative dose of 10-20 krad. We report the successful preparation of an HTS bearing cosmic background radiation, the fabrication and testing of a bulk superconducting device operating in the Columbus laboratory of the International Space Station (ISS). The Magvector/MFX experiment operates the last four years at the ISS. It measures the interaction of a YBCO HTS with the Earth magnetic field using sensitive flux gate sensors in μT level. Laboratory shielding results are given. Dependent on the bulk conductivity at T>T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> and T<;T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> the Earth magnetic field interaction causes distortions of the surrounding electromagnetic (EM) field. Possible benefits of HTS bulk devices on applications in space will be discussed.

Deformation of cellular components of bone forming cells when exposed to a magnetic field

It has been suggested that alignment control of biological macromolecules and structures is possible when the diamagnetic energy is sufficient to overcome the thermal energy. Strong magnetic fields of several Tesla (T) have previously been shown to enable the observation of the magnetic orientations of protein fibers and suspended or adherent cells. In the present study, the fine structure of a bone-forming osteoblast cell line was observed in real-time under strong static magnetic fields of up to 5 T. The magnetic field was applied normal to the adhering surface, and induced slight deformation of cellular shape under bright field illumination. A newly developed dark field observation method presented more precise analysis of the inner structures of the cells in strong magnetic fields. Specifically, structures with a round appearance were clearly visualized around the cell nucleus using the electromagnetic illumination. In addition to the magnetically induced swelling of the round structures—which showed differences in diameter of several micrometers—color changes for these intracellular components were also detected using this technique. A high-resolution analysis of fine cellular structure based on the magnetic orientation of intracellular components including microtubules is proposed.

Control of Y-211 content in bulk YBCO superconductors fabricated by a buffer-aided, top seeded infiltration and growth melt process

Bulk (RE)–Ba–Cu–O ((RE)BCO, where RE stands for rare-earth), single grain superconductors can trap magnetic fields of several tesla at low temperatures and therefore can function potentially as high field magnets. Although top seeded melt growth (TSMG) is an established process for fabricating relatively high quality single grains of (RE)BCO for high field applications, this technique suffers from inherent problems such as sample shrinkage, a large intrinsic porosity and the presence of (RE)2BaCuO5 (RE-211)-free regions in the single grain microstructure. Seeded infiltration and growth (SIG), therefore, has emerged as a practical alternative to TSMG that overcomes many of these problems. Until now, however, the superconducting properties of bulk materials processed by SIG have been inferior to those fabricated using the TSMG technique. In this study, we identify that the inferior properties of SIG processed bulk superconductors are related to the presence of a relatively large Y-211 content (∼41.8%) in the single grain microstructure. Controlling the RE-211 content in SIG bulk samples is particularly challenging because it is difficult to regulate the entry of the liquid phase into the solid RE-211 preform during the infiltration process. In an attempt to solve this issue, we have investigated the effect of careful control of both the infiltration temperature and the quantity of liquid phase powder present in the sample preforms prior to processing. We conclude that careful control of the infiltration temperature is the most promising of these two process variables. Using this knowledge, we have fabricated successfully a YBCO bulk single grain using the SIG process of diameter 25 mm that exhibits a trapped field of 0.69 T at 77 K, which is the largest value reported to date for a sample fabricated by the SIG technique.

Enhanced Low-Field Magnetoresistance in La0.71Sr0.29MnO3 Nanoparticles Synthesized by the Nonaqueous Sol–Gel Route

In colossal magnetoresistive (CMR) materials, magnetic fields of several tesla are typically required to exhibit large changes in electrical resistance, and hence, materials should be engineered to provide a more sensitive MR response at lower fields for their viability in practical applications. Enhanced low-field magnetoresistance (LFMR) was observed in highly ferromagnetic ∼20 nm La0.71Sr0.29MnO3 particles synthesized by the nonaqueous sol–gel route. The enhanced LFMR of the nanoparticles (NPs) reaches 29.8% at 30 K with 50 mT, and the high-field magnetoresistance was 56% with a 5000 mT applied field. The large LFMR effect can be attributed to the spin-polarized tunneling across the ∼1.3 nm thick natural grain boundaries. The weaker MR effect below 30 K was attributed to the re-entrant spin glass at the core of the NPs and surface spin glass phase that could be eliminated with lower and higher applied fields, respectively. The magnetic and MR properties of the NPs were compared to those of the correspo...

High Force Magnetic Levitation Using Magnetized Superconducting Bulks as a Field Source for Bearing Applications

Abstract The ability of high temperature superconducting bulks to trap magnetic fields of several tesla allows them to generate very high levitation force. This paper reports the development of a bulk-bulk superconducting rotary bearing design which uses superconducting bulks on both the rotor and the stator. An evaluation is made of the effectiveness of pulsed fields for magnetizing bulks. Modeling of the bulks using the perfectly trapped flux model is also reported to assess the limits of the bearing design. The results demonstrate the feasibility of a (RE)BCO-MgB2 bulk bearing capable of force densities of the order of 100N/cm2. The design and construction of a unique system capable of magnetizing a 25 mm (RE)BCO bulk and measuring levitation force between this bulk and a coaxial MgB2 hollow cylinder is outlined.

Onset of magnetism stimulated by H absorption in UNiAl-UFeAl

Weak itinerant antiferromagnetism of UNiAl is rapidly suppressed by Fe doping. Magnetic order reappears as weak ferromagnetism in UNi0.75Fe0.25Al. The onset of magnetism can be shifted by H absorption. UNi0.85Fe0.15Al hydride is an antiferromagnet with TN approx. 70 K. Hydrogenating UNi0.70Fe0.30Al produces a ferromagnet (TC = 90 K). Here we describe the compound with 20% of Fe and its hydride. The proximity to magnetism shows up as non-Fermi liquid behavior, detected in specific heat as upturn, followed down to 0.3 K, which is gradually suppressed in magnetic fields of several tesla. The hydride was found rather unstable, releasing H at ambient conditions, which made it unsuitable for the specific heat measurement. Magnetization study detected that the hydride shows up as ferromagnet TC ≈ 98 K.

Fluorine-19 NMR Chemical Shift Probes Molecular Binding to Lipid Membranes

The binding of amphiphilic molecules to lipid bilayers is followed by 19F NMR using chemical shift and line shape differences between the solution and membrane-tethered states of -CF 3 and -CHF 2 groups. A chemical shift separation of 1.6 ppm combined with a high natural abundance and high sensitivity of 19F nuclei offers an advantage of using 19F NMR spectroscopy as an efficient tool for rapid time-resolved screening of pharmaceuticals for membrane binding. We illustrate the approach with molecules containing both fluorinated tails and an acrylate moiety, resolving the signals of molecules in solution from those bound to synthetic dimyristoylphosphatidylcholine bilayers both with and without magic angle sample spinning. The potential in vitro and in vivo biomedical applications are outlined. The presented method is applicable with the conventional NMR equipment, magnetic fields of several Tesla, stationary samples, and natural abundance isotopes.

Microstructure and $J_{\rm C}$ Characteristics of Er123 Films With Artificial Pinning Centers

Critical current density and surface resistance are evaluated for dilute Zn substituted high quality ErBa2Cu3O7-zeta films. Dilute Zn substituted ErBa2Cu3O7-zeta films are grown on SrTiO3 substrates by a pulsed laser deposition technique. Targets used in the experiments are un-substituted, 0.3at. %, 0.5at.%, 1.0at.% and 10at.% Zn substituted ErBa2Cu3O7-zeta ceramics. Crystal structures, field angular dependence of critical current density and surface resistance are evaluated. Zn substituting into YBa2Cu3O7-zeta has been studied for understanding the origin of oxide superconductivity with substituting level of several %. In this study, dilute Zn below 1.0 at.% is mainly adopted. Further substitution reduces its critical temperature. We intended to introduce zero-dimensional superconductivity killer atoms into CuO2 plane as artificial pinning centers. The obtained Zn substituted ErBa2Cu3O7-zeta films are c-axis oriented without peaks from other phases. The sharp drop temperature of surface resistance decreases as the Zn substitution. However, the surface resistance at a low temperature around 20 K is almost the same among the ErBa2Cu3O7-zeta films with different Zn substitution. We also measured the field angular dependence of critical current density of the Zn substituted ErBa2Cu3O7-zeta films. There are no strong angular dependences. Dilute zinc substitution increases critical current density for almost of all directions. However, in a high magnetic field of several tesla, pinning force around the field direction of a-axis is enhanced. Double introduction of one dimensional artificial pinning centers such as BaZrO3 nano-rods and zero dimensional artificial pinning centers is thought to be very effective for increasing critical current density for power cable applications.

Giant Magnetostriction and Flux Jumps in Superconducting Nb3Al Polycrystalline Slab

Transverse and longitudinal magnetostriction of a large polycrystalline slab of Nb3Al superconductor was investigated by the strain gauge technique. At 4.2 K and in an external magnetic field of several Tesla the vertical width of transverse magnetostriction hysteresis loop was found to be of an order of 10−4. In a wide range of temperatures and external magnetic fields we observed the phenomenon of giant jumps of both transverse and longitudinal magnetostriction caused by thermomagnetic avalanches. The shapes of the magnetostriction hysteresis loops are also influenced by the phenomenon of the second maximum of the critical current density, called as a peak or fishtail effect. Experimental results can be understood in the framework of the model of the magnetostriction induced by pinning forces.

Pinning of the Vortex System and Magnetostriction of Superconductors

Hard type-II superconductors usually reveal a large, of the order of 10−5 or 10−4, magnetostriction in the external magnetic field of several Tesla. Such a strong magnetostriction can be well understood in the framework of the model of the pinning-induced magnetostriction. Although the assumptions of this model are easy to understand, the solution of the problem for realistic sample shapes is difficult, because the stress induced in the sample volume by the screening currents has non uniform distribution and it may also change the sample shape. The model of pinning-induced magnetostriction is insufficient to explain all magnetostriction results in superconductors. Sometimes, it is necessary to consider also other mechanisms of the magnetostriction. Magnetostriction of superconductors was analyzed theoretically and studied experimentally in a large number of both conventional and high temperature superconductors. In this paper we present a review of the most characteristic results. We also present the phenomenon of giant magnetostriction jumps, which is closely related to the phenomenon of giant flux jumps or thermomagnetic instabilities in type-II superconductors.

Sign inversion of the high-field Hall slope in epitaxialLa0.5Ca0.5MnO3thin films

Magnetic and electrical properties of thin epitaxial films of the manganite ${\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Ca}}_{x}{\mathrm{MnO}}_{3}$ $(x\ensuremath{\approx}0.5)$ grown by pulsed laser deposition were investigated. The $x=0.5$ composition corresponds to a half-filled ${e}_{g}$ band and is situated on the border between ferromagnetic-metallic and antiferromagnetic-insulating behavior at low temperatures. Both different types of electrical behaviors are observed in samples with similar deposition parameters. This duality may be attributed to phase separation and the occurrence of percolating paths. The insulating ${\mathrm{La}}_{0.5}{\mathrm{Ca}}_{0.5}{\mathrm{MnO}}_{3}$ samples become metalliclike when magnetic fields of several tesla are applied. Hereby, resistivity drops up to six orders of magnitude occur at 50 K and 12 T. Hall effect measurements on a sample with spontaneous insulator-metal transition show a sign inversion of the high-field Hall slope around 106 K.

Ca-doping-induced enhancement of the critical currents of coated conductors grown by ion-beam-assisted deposition

One of the most promising technologies for the fabrication of high-Tc cables is the ion-beam-assisted deposition (IBAD) technique. The performance of the superconductors fabricated by IBAD, and the fabrication costs, are to a great extent determined by the critical current densities of the superconductors’ grain boundaries. Since, in bicrystalline samples, overdoping has been found to improve the transport properties of grain boundaries in high-Tc superconductors, we have explored whether overdoping also enhances the critical currents of IBAD samples. The measurements show that, depending on the critical current density of the superconducting film, Jc (77 K) is increased by factors up to 2.2, also in applied magnetic fields of several tesla.

High-temperature superconductor bulk magnets that can trap magnetic fields of over 17 tesla at 29 K

Large-grain high-temperature superconductors of the form RE-Ba-Cu-O (where RE is a rare-earth element) can trap magnetic fields of several tesla at low temperatures, and so can be used for permanent magnet applications. The magnitude of the trapped field is proportional to the critical current density and the volume of the superconductor. Various potential engineering applications for such magnets have emerged, and some have already been commercialized. However, the range of applications is limited by poor mechanical stability and low thermal conductivity of the bulk superconductors; RE-Ba-Cu-O magnets have been found to fracture during high-field activation, owing to magnetic pressure. Here we present a post-fabrication treatment that improves the mechanical properties as well as thermal conductivity of a bulk Y-Ba-Cu-O magnet, thereby increasing its field-trapping capacity. First, resin impregnation and wrapping the materials in carbon fibre improves the mechanical properties. Second, a small hole drilled into the centre of the magnet allows impregnation of Bi-Pb-Sn-Cd alloy into the superconductor and inclusion of an aluminium wire support, which results in a significant enhancement of thermal stability and internal mechanical strength. As a result, 17.24 T could be trapped, without fracturing, in a bulk Y-Ba-Cu-O sample of 2.65 cm diameter at 29 K.

Phonon-assisted magnetopolaron effect in diluted magnetic semiconductors

A phonon-assisted magnetopolaron effect in diluted magnetic semiconductors is theoretically investigated. It is shown that the binding energy of magnetic polarons can be substantially enhanced if coupling between the magnetic and phonon subsystems is taken into account. In the particular case of ``soft'' lattice dynamics, the stability range of the hole-induced magnetic polaron can be extended to temperatures of a few tens of kelvin and magnetic fields of several tesla.

Oriented Sm2(Co, Cu, Fe, Zr)17 permanent magnets produced by solidification in a magnetic field

Oriented samples of Sm2(Co, Cu, Fe, Zr)17 have been produced by solidification from the liquid state in the presence of a magnetic field of several Tesla, their easy magnetization axis being in the direction of the applied magnetic field. This orientation allowed the development of a new process to produce anisotropic permanent magnets without using the metallurgical powder technology. This is the case for the samarium–cobalt magnets presented in this paper. In particular, it is shown that the chemical composition used to produce them might be adapted from those used for sintered Sm2(Co, Cu, Fe, Zr)17 magnets, in order to optimize their magnetic properties.

Innovating approaches to the generation of intense magnetic fields : design and optimization of a 4 Tesla permanent magnet flux source

An original permanent magnet flux source is designed in order to generate a magnetic field of several Tesla. The magnet configuration and discretization of the structure are optimized with the help of numerical simulation software developed at LEG (DIPOLE-3D, FLUX2D & FLUX3D). The model of spheroidal flux source presented in the paper creates a field in excess of 4.3 T in a central volume of O 6 mm/spl times/h 2.8 mm with external diameter /spl ap/O100 mm. A prototype is in the final assembly stage, designed for X-ray dichroism experiments at the European Synchrotron Radiation Facility (ESRF) in Grenoble.