Magnetic moment formation due to arsenic vacancies in LaFeAsO-derived superconductors

Czech Academy of Sciences Publication Activity Database

Kikoin, K.; Drechsler, S.L.; Koepernik, K.; Málek, Jiří; van den Brink, J.

2015-01-01

Roč. 5, Jul (2015), s. 11280 ISSN 2045-2322 Institutional support: RVO:68378271 Keywords : high-temperature superconductivity, transition metal impurities * iron-based superconductors * pnictides Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 5.228, year: 2015

Behaviour of magnetic superconductors in a magnetic field

International Nuclear Information System (INIS)

Buzdin, A.I.

1984-01-01

The behaviour of magnetic superconductors with close ferromagnetic and superconducting transition temperatures in a magnetic field is considered. It is shown that on lowering of the temperature the superconducting transition changes from a second to first order transition. The respective critical fields and dependence of the magnetization on the magnetic field and temperature are found. The magnetization discontinuity in the vortex core in magnetic superconductors is noted. Due to this property and the relatively large scattering cross section, magnetic superconductors are convenient for studying the superconducting vortex lattice by neutron diffraction techniques

Modelling of bulk superconductor magnetization

International Nuclear Information System (INIS)

Ainslie, M D; Fujishiro, H

2015-01-01

This paper presents a topical review of the current state of the art in modelling the magnetization of bulk superconductors, including both (RE)BCO (where RE = rare earth or Y) and MgB 2 materials. Such modelling is a powerful tool to understand the physical mechanisms of their magnetization, to assist in interpretation of experimental results, and to predict the performance of practical bulk superconductor-based devices, which is particularly important as many superconducting applications head towards the commercialization stage of their development in the coming years. In addition to the analytical and numerical techniques currently used by researchers for modelling such materials, the commonly used practical techniques to magnetize bulk superconductors are summarized with a particular focus on pulsed field magnetization (PFM), which is promising as a compact, mobile and relatively inexpensive magnetizing technique. A number of numerical models developed to analyse the issues related to PFM and optimise the technique are described in detail, including understanding the dynamics of the magnetic flux penetration and the influence of material inhomogeneities, thermal properties, pulse duration, magnitude and shape, and the shape of the magnetization coil(s). The effect of externally applied magnetic fields in different configurations on the attenuation of the trapped field is also discussed. A number of novel and hybrid bulk superconductor structures are described, including improved thermal conductivity structures and ferromagnet–superconductor structures, which have been designed to overcome some of the issues related to bulk superconductors and their magnetization and enhance the intrinsic properties of bulk superconductors acting as trapped field magnets. Finally, the use of hollow bulk cylinders/tubes for shielding is analysed. (topical review)

Dressed topological insulators. Rashba impurity, Kondo effect, magnetic impurities, proximity-induced superconductivity, hybrid systems

International Nuclear Information System (INIS)

Posske, Thore Hagen

2016-01-01

Topological insulators are electronic phases that insulate in the bulk and accommodate a peculiar, metallic edge liquid with a spin-dependent dispersion. They are regarded to be of considerable future use in spintronics and for quantum computation. Besides determining the intrinsic properties of this rather novel electronic phase, considering its combination with well-known physical systems can generate genuinely new physics. In this thesis, we report on such combinations including topological insulators. Specifically, we analyze an attached Rashba impurity, a Kondo dot in the two channel setup, magnetic impurities on the surface of a strong three-dimensional topological insulator, the proximity coupling of the latter system to a superconductor, and hybrid systems consisting of a topological insulator and a semimetal. Let us summarize our primary results. Firstly, we determine an analytical formula for the Kondo cloud and describe its possible detection in current correlations far away from the Kondo region. We thereby rely on and extend the method of refermionizable points. Furthermore, we find a class of gapless topological superconductors and semimetals, which accommodate edge states that behave similarly to the ones of globally gapped topological phases. Unexpectedly, we also find edge states that change their chirality when affected by sufficiently strong disorder. We regard the presented research helpful in future classifications and applications of systems containing topological insulators, of which we propose some examples.

Dressed topological insulators. Rashba impurity, Kondo effect, magnetic impurities, proximity-induced superconductivity, hybrid systems

Energy Technology Data Exchange (ETDEWEB)

Posske, Thore Hagen

2016-02-26

Topological insulators are electronic phases that insulate in the bulk and accommodate a peculiar, metallic edge liquid with a spin-dependent dispersion. They are regarded to be of considerable future use in spintronics and for quantum computation. Besides determining the intrinsic properties of this rather novel electronic phase, considering its combination with well-known physical systems can generate genuinely new physics. In this thesis, we report on such combinations including topological insulators. Specifically, we analyze an attached Rashba impurity, a Kondo dot in the two channel setup, magnetic impurities on the surface of a strong three-dimensional topological insulator, the proximity coupling of the latter system to a superconductor, and hybrid systems consisting of a topological insulator and a semimetal. Let us summarize our primary results. Firstly, we determine an analytical formula for the Kondo cloud and describe its possible detection in current correlations far away from the Kondo region. We thereby rely on and extend the method of refermionizable points. Furthermore, we find a class of gapless topological superconductors and semimetals, which accommodate edge states that behave similarly to the ones of globally gapped topological phases. Unexpectedly, we also find edge states that change their chirality when affected by sufficiently strong disorder. We regard the presented research helpful in future classifications and applications of systems containing topological insulators, of which we propose some examples.

Electron tunneling into superconducting indium and lead films containing the magnetic impurity manganese

International Nuclear Information System (INIS)

Tsang, J.K.

1980-01-01

Tunneling measurements of quench-condensed In-Mn and Pb-Mn alloy films were made. The results were compared with Shiba's theory of superconductors containing magnetic impurities. The localized excited impurity states predicted by Shiba's theory were observed in both alloys. In addition to s-wave scattering, it was necessary to include p- and d-wave scattering of the conduction electrons in the theory in order to explain the experimental data. Partial agreement between the theory and the experimental data was obtained using phase shifts from band calculations by A.B. Kunz. The results on In-Mn also agree with thermal conductivity data

Numerical analysis of thermally actuated magnets for magnetization of superconductors

Energy Technology Data Exchange (ETDEWEB)

Li Quan; Yan Yu; Rawlings, Colin; Coombs, Tim, E-mail: ql229@cam.ac.u [EPEC Superconductivity Group, Engineering Department, University of Cambridge, Trumpington Street. Cambridge, CB2 1PZ (United Kingdom)

2010-06-01

Superconductors, such as YBCO bulks, have extremely high potential magnetic flux densities, comparing to rare earth magnets. Therefore, the magnetization of superconductors has attracted broad attention and contribution from both academic research and industry. In this paper, a novel technique is proposed to magnetize superconductors. Unusually, instead of using high magnetic fields and pulses, repeatedly magnetic waves with strength of as low as rare earth magnets are applied. These magnetic waves, generated by thermally controlling a Gadolinium (Gd) bulk with a rare earth magnet underneath, travel over the flat surface of a YBCO bulk and get trapped little by little. Thus, a very small magnetic field can be used to build up a very large magnetic field. In this paper, the modelling results of thermally actuated magnetic waves are presented showing how to transfer sequentially applied thermal pulses into magnetic waves. The experiment results of the magnetization of YBCO bulk are also presented to demonstrate how superconductors are progressively magnetized by small magnetic field

Numerical analysis of thermally actuated magnets for magnetization of superconductors

International Nuclear Information System (INIS)

Li Quan; Yan Yu; Rawlings, Colin; Coombs, Tim

2010-01-01

Superconductors, such as YBCO bulks, have extremely high potential magnetic flux densities, comparing to rare earth magnets. Therefore, the magnetization of superconductors has attracted broad attention and contribution from both academic research and industry. In this paper, a novel technique is proposed to magnetize superconductors. Unusually, instead of using high magnetic fields and pulses, repeatedly magnetic waves with strength of as low as rare earth magnets are applied. These magnetic waves, generated by thermally controlling a Gadolinium (Gd) bulk with a rare earth magnet underneath, travel over the flat surface of a YBCO bulk and get trapped little by little. Thus, a very small magnetic field can be used to build up a very large magnetic field. In this paper, the modelling results of thermally actuated magnetic waves are presented showing how to transfer sequentially applied thermal pulses into magnetic waves. The experiment results of the magnetization of YBCO bulk are also presented to demonstrate how superconductors are progressively magnetized by small magnetic field

Influence of the impurity-scattering on zero-bias conductance peak in ferromagnet/insulator/d-wave superconductor junctions

CERN Document Server

Yoshida, N; Itoh, H; Tanaka, Y; Inoue, J I; Kashiwaya, S

2003-01-01

Effects of impurity-scattering on a zero-bias conductance peak in ferromagnet/insulator/d-wave superconductor junctions are theoretically studied. The impurities are introduced through the random potential in ferromagnets near the junction interface. As in the case of normal-metal/insulator/d-wave superconductor junctions, the magnitude of zero-bias conductance peak decreases with increasing the degree of disorder. However, when the magnitude of the exchange potential in ferromagnet is sufficiently large, the random potential can enhance the zero-bias conductance peak in ferromagnetic junctions. (author)

Correction of magnetization sextupole in one-meter long dipole magnets using passing superconductor

International Nuclear Information System (INIS)

Green, M.A.; Althaus, R.F.; Barale, P.J.; Benjegerdes, R.W.; Gilbert, W.S.; Green, M.I.; Scanlan, R.M.

1990-03-01

The generation of higher multipoles due to the magnetization of the superconductor in the dipoles of the SSC is a problem during injection of the beam into the machine. The use of passive superconductor was proposed some years ago to correct the magnetization sextupole in the dipole magnet. This paper presents the LBL test results in which the magnetization sextupole was greatly reduced in two one-meter long dipole magnets by the use of passive superconductor mounted on the magnet bore tube. The magnetization sextupole was reduced a factor of five on one magnet and a factor of eight on the other magnet using this technique. Magnetization decapole was also reduced by the passive superconductor. The passive superconductor method of correction also reduced the temperature dependence of the magnetization multipoles. In addition, the drift in the magnetization sextupole due to flux creep was also reduced. Passive superconductor correction appears to be a promising method of correcting out the effects of superconductor magnetization in SSC dipoles and quadrupoles. 10 refs., 6 figs

Axial force in a superconductor magnet journal bearing

Science.gov (United States)

Postrekhin, E.; Chong, Wang; Ki Bui, Ma; Chen, Quark; Chu, Wei-Kan

Using superconductors and magnets, a journal bearing could be made from a permanent magnet cylinder in a superconductor ring. We have assembled a prototype superconductor magnet journal bearing of this configuration, and investigated the behavior of the axial force that it can provide. We have put together a numerical model of the interaction between the permanent magnet and the superconductor that is capable of describing these experimental results semi-quantitatively. Combining direct experimental measurements and using the numerical models proposed, we have achieved a qualitative understanding of the behavior of the axial force and its relationship of to the dimensions of the magnet and material quality such as the homogeneity of the superconductor that constitute the bearing.

Proposal of Magnetic Circuit using Magnetic Shielding with Bulk-Type High Tc Superconductors

Science.gov (United States)

Fukuoka, Katsuhiro; Hashimoto, Mitsuo; Tomita, Masaru; Murakami, Masato

Recently, bulk-type high Tc superconductors having a characteristic of critical current density over 104 A/cm2 in liquid nitrogen temperature (77K) on 1T, can be produced. They are promising for many practical applications such as a magnetic bearing, a magnetic levitation, a flywheel, a magnetic shielding and others. In this research, we propose a magnetic circuit that is able to use for the magnetic shield of plural superconductors as an application of bulk-type high Tc superconductors. It is a closed magnetic circuit by means of a toroidal core. Characteristics of the magnetic circuit surrounded with superconductors are evaluated and the possibility is examined. As the magnetic circuit of the ferrite core is surrounded with superconductors, the magnetic flux is shielded even if it leaked from the ferrite core.

Neutron-scattering studies of magnetic superconductors

International Nuclear Information System (INIS)

Sinha, S.K.; Crabtree, G.W.; Hinks, D.G.; Mook, H.A.; Pringle, O.A.

1982-01-01

Results obtained in the last few years obtained by neutron diffraction on the nature of the magnetic ordering in magnetic superconductors are reviewed. Emphasis is given to studies of the complex intermediate phase in ferromagnetic superconductors where both superconductivity and ferromagnetism appear to coexist

Stability of magnets levitated above superconductors

International Nuclear Information System (INIS)

Davis, L.C.; Logothetis, E.M.; Soltis, R.E.

1988-01-01

The stability of a permanent magnet levitated above a slab of hard superconductor is considered. The force on a dipole magnet over a perfectly diamagnetic disk is calculated. It is found that the radial component of the force is directed outward and is 10%--20% of the image (vertical) force near the edge. Estimates of the magnetic friction force due to flux motion in a hard superconductor are made using Bean's model. The magnitude of the magnetic friction is large enough to stabilize the magnet over most of the disk for typical values of the critical current in ceramic superconductors (∼10 3 A/cm 2 ), but too small for the highest values reported (>10 6 A/cm 2 ). It is conjectured that flux trapping due to inhomogeneities gives rise to transient restoring forces

High temperature superconductor accelerator magnets

NARCIS (Netherlands)

van Nugteren, J.

2016-01-01

For future particle accelerators bending dipoles are considered with magnetic fields exceeding 20T. This can only be achieved using high temperature superconductors (HTS). These exhibit different properties from classical low temperature superconductors and still require significant research and

Effects of magnetic atoms on the properties of ternary superconductors

International Nuclear Information System (INIS)

Dunlap, B.D.; Shenoy, G.K.

1980-01-01

Until recently it has been commonly accepted that small impurities of magnetic atoms were severely detrimental to superconductivity, and that superconductivity and long-range magnetic ordering could not occur in the same materials. In known binary and pseudo-binary compounds, this is still the case. However, many recent experiments on ternary superconductors have shown that the effects of magnetism are considerably more complex. In some cases, the addition of magnetic atoms has been found to enhance superconducting properties by increasing the superconducting critical field, without significantly lowering the transition temperature. In many cases, compounds will show both superconducting and long range magnetic ordering transitions. The destruction of superconductivity by ferromagnetic ordering and the coexistence of superconductivity with antiferromagnetic ordering is now well established. Hyperfine interaction measurements have played a significant role in the investigations of these materials, including measurement of the magnitude of the exchange interaction between rare-earth spin and conduction electron spin, elucidation of the mechanism for critical field enhancement, specification of crystalline field ground states, and studies of the nature of magnetic ordering

Unconventional superconductivity in heavy fermionic and high-Tc superconductors

International Nuclear Information System (INIS)

Volovik, G.E.

1989-01-01

Splitting of the superconducting transition and glass spectrum in heavy fermion companies and oxide superconductors are discussed. The multicomponent order parameter leads to splitting of transition due to magnetic field, impurities, orthorhombic distortion, etc... Linear specific heat in oxide superconductors may be explained in terms of the Fermi-surface arising in superconducting state if interband is pairing strong enough

High temperature superconductor cable concepts for fusion magnets

CERN Document Server

AUTHOR|(CDS)2078397

2013-01-01

Three concepts of high temperature superconductor cables carrying kA currents (RACC, CORC and TSTC) are investigated, optimized and evaluated in the scope of their applicability as conductor in fusion magnets. The magnetic field and temperature dependence of the cables is measured; the thermal expansion and conductivity of structure, insulation and filling materials are investigated. High temperature superconductor winding packs for fusion magnets are calculated and compared with corresponding low temperature superconductor cases.

Recent status of superconductors for accelerator magnets

International Nuclear Information System (INIS)

Greene, A.F.

1992-01-01

A survey is given of superconductor wire and cable which has been or will be used for construction of dipole magnets for all of the large European and US superconducting accelerator rings. Included is a simplified view of the construction methods and operating requirements of an accelerator dipole magnet, with emphasis on required superconductor performance. The methods of fabricating Nb-Ti superconductors are described, including the critical parameters and materials requirements. The superconductor performance requirements are summarized in an effort to relate why these are important to accelerator designers. Some of the recently observed time dependent effects are covered briefly

Workshop on accelerator magnet superconductors. Proceedings

International Nuclear Information System (INIS)

2004-01-01

The workshop on accelerator magnet superconductors has gathered 102 registered participants from research laboratories, universities and industry. 8 European companies, active in superconducting materials and cables were present. This workshop has been organized to deal with the status of the world research and development on superconducting materials and cables for high field magnets (B > 10 T). The workshop has also reviewed the status of high temperature superconductors and transmission line cables for potential use in low field superconducting magnets for injectors and beam transfer lines, as well as cables for pulsed magnets that might be used in future hadron colliders or injectors

Workshop on accelerator magnet superconductors. Proceedings

Energy Technology Data Exchange (ETDEWEB)

NONE

2004-07-01

The workshop on accelerator magnet superconductors has gathered 102 registered participants from research laboratories, universities and industry. 8 European companies, active in superconducting materials and cables were present. This workshop has been organized to deal with the status of the world research and development on superconducting materials and cables for high field magnets (B > 10 T). The workshop has also reviewed the status of high temperature superconductors and transmission line cables for potential use in low field superconducting magnets for injectors and beam transfer lines, as well as cables for pulsed magnets that might be used in future hadron colliders or injectors.

Exotic magnetic states in Pauli-limited superconductors.

Science.gov (United States)

Kenzelmann, M

2017-03-01

Magnetism and superconductivity compete or interact in complex and intricate ways. Here we review the special case where novel magnetic phenomena appear due to superconductivity, but do not exist without it. Such states have recently been identified in unconventional superconductors. They are different from the mere coexistence of magnetic order and superconductivity in conventional superconductors, or from competing magnetic and superconducting phases in many materials. We describe the recent progress in the study of such exotic magnetic phases, and articulate the many open questions in this field.

High-T/sub c/ superconductor and its use in superconducting magnets

International Nuclear Information System (INIS)

Green, M.A.

1988-02-01

Many of the proposed uses for the high-T/sub c/ superconductor involve the creation of a magnetic field using superconducting coils. This report will assess what is known about the high-T/sub c/ superconductors and take a realistic look at their potential use in various kinds of superconducting magnets. Based on what is known about the high-T/sub c/ superconductors, one can make a ''wish list'' of things that will make such materials useful for magnets. Then, the following question is asked. If one had a high-T/sub c/ superconductor with the same properties as modern niobium-titanium superconductor, how would the superconductor work in a magnet environment? Finally, this report will show the potential impact of the ideal high-T/sub c/ superconductor on: 1) accelerator dipole and quadrupole magnets, 2) superconducting magnets for use in space, and 3) superconducting solenoids for magnetic resonance imaging. 78 refs., 11 tabs

Effect of normal impurities on anisotropic superconductors with variable density of states

Science.gov (United States)

Whitmore, M. D.; Carbotte, J. P.

1982-06-01

We develop a generalized BCS theory of impure superconductors with an anisotropic electron-electron interaction represented by the factorizable model introduced by Markowitz and Kadanoff, and a variable electronic density of states N(ɛ), assumed to peak at the Fermi energy, which is modeled by a Lorentzian superimposed on a uniform background. As the impurity scattering is increased, the enhancement of T c by both the anisotropy and the peak in N(ɛ) is washed out. The reduction is investigated for different values of the anisotropy and different peak heights and widths. It is concluded that the effects of anisotropy and the peak are reduced together in such a way that any effect due to anisotropy is not easily distinguishable from that due to the peak.

High Temperature Superconductor Accelerator Magnets

CERN Document Server

AUTHOR|(CDS)2079328; de Rijk, Gijs; Dhalle, Marc

2016-11-10

For future particle accelerators bending dipoles are considered with magnetic fields exceeding $20T$. This can only be achieved using high temperature superconductors (HTS). These exhibit different properties from classical low temperature superconductors and still require significant research and development before they can be applied in a practical accelerator magnet. In order to study HTS in detail, a five tesla demonstrator magnet named Feather-M2 is designed and constructed. The magnet is based on ReBCO coated conductor, which is assembled into a $10kA$ class Roebel cable. A new and optimized Aligned Block layout is used, which takes advantage of the anisotropy of the conductor. This is achieved by providing local alignment of the Roebel cable in the coil windings with the magnetic field lines. A new Network Model capable of analyzing transient electro-magnetic and thermal phenomena in coated conductor cables and coils is developed. This model is necessary to solve critical issues in coated conductor ac...

Real space mapping of Yu-Shiba-Rusinov states of an extended magnetic scatterer on a conventional superconductor

Energy Technology Data Exchange (ETDEWEB)

Etzkorn, Markus; Eltschka, Matthias; Jaeck, Berthold; Topp, Andreas; Ast, Christian R. [Max-Planck-Institute for Solid State Research, 70569 Stuttgart (Germany); Kern, Klaus [Max-Planck-Institute for Solid State Research, 70569 Stuttgart (Germany); Ecole Polytechnique Federale de Lausanne, 1015 Lausanne (Switzerland)

2016-07-01

The interaction of a local magnetic impurity with a superconductor causes the formation of Yu-Shiba-Rusinov (YSR)states in the vicinity of the impurity. These have recently received increasing attention in the context of Majorana Fermions and other exotic states that might be created from the mutual interplay. YSR states have been extensively studied by scanning tunneling microscopy and so far have been discussed mainly in the limit of point scattering impurities. Here we present our investigations of the local properties of single magnetic Copper-Phthalocynane molecules on the (5x1) reconstructed, superconducting V(100) surface measured at 15 mK temperature. We find very intense YSR states with energies that depend on the precise absorbtion geometry of the molecule. At the same time we find no indication of a local suppression of the superconducting gap around the impurity. We follow the state evolution in real space for about 3 nm corresponding to about three orders of magnitude in spectral intensity. The spectra display rich structure with local variations in the electron-hole asymmetries. The observed intensity changes in the spectra can not be described on the basis of a single point like scattering potential.

Upper critical magnetic field of superconducting films with magnetic impurities

International Nuclear Information System (INIS)

Lemberger, T.R.

1978-01-01

The upper critical magnetic field, H/sub c2/(T), of In-Mn and Pb-Mn alloy films was measured. H/sub c2/ was determined from the resistance of the films. The results were compared with the theory of Fulde and Maki. This theory assumes that the electron-phonon coupling is weak, and that the interaction between the impurity spins and the conduction electron spins is weak. The theory predicts that the pair-breaking effect of the magnetic impurities is temperature-independent, and that the pair-breaking effects of the magnetic impurities and the applied magnetic field are additive. Furthermore, it predicts explicitly the temperature dependence of H/sub c2/. The temperature dependence of H/sub c2/ for the In-Mn alloy films is well described by the Fulde-Maki theory, despite the moderately strong electron-phonon coupling and the strong interaction between the impurity spins and the conduction electron spins. The temperature dependence of H/sub c2/ for the Pb-Mn alloy films is not well described by the Fulde-Maki theory, probably due to the strong electron-phonon coupling in Pb. However, even without a quantitatively correct theory, one can conclude from the Pb-Mn data that the pair-breaking effect of the magnetic impurities is temperature independent, and that the pair-breaking effects of the magnetic impurities and the applied magnetic field are additive. For some of the Pb-Mn alloy films, there was a region of positive curvature in H/sub c2/(T) near the zero-field transition temperature. This positive curvature is not understood

Photographing magnetic fields in superconductors

International Nuclear Information System (INIS)

Harrison, R.B.; Wright, L.S.

Magneto-optic techniques coupled with high-speed photography are being used to study the destruction of superconductivity by a magnetic field. The phenomenon of superconductivity will be introduced with emphasis placed on the properties of type I and type II superconductors in a magnetic field. The Faraday effect and its application to the study of the penetration of magnetic fields into these superconductors will be described; the relative effectiveness of some types of paramagnetic glass will be demonstrated. A number of cinefilms will be shown to illustrate the versatility of the magneto-optic method for observing flux motion and patterns. The analysis of data obtained from a high speed film (10,200 fps) of a flux jump in Nb-Zr will be presented and discussed

Effect of normal impurities on anisotropic superconductors with variable density of states

International Nuclear Information System (INIS)

Whitmore, M.D.; Carbotte, J.P.

1982-01-01

We develop a generalized BCS theory of impure superconductors with an anisotropic electron--electron interaction represented by the factorizable model introduced by Markowitz and Kadanoff, and a variable electronic density of states N(epsilon-c), assumed to peak at the Fermi energy, which is modeled by a Lorentzian superimposed on a uniform background. As the impurity scattering is increased, the enhancement of T/sub c/ by both the anisotropy and the peak in N(epsilon-c) is washed out. The reduction is investigated for different values of the anisotropy and different peak heights and widths. It is concluded that the effects of anisotropy and the peak are reduced together in such a way that any effect due to anisotropy is not easily distinguishable from that due to the peak

Magnetization effects from the g-2 inflector magnet superconductor

International Nuclear Information System (INIS)

Green, M.A.; Meng, W.

1994-01-01

The g-2 muon storage ring at Brookhaven National Laboratory will have a 1.7 meter long superconducting inflector magnet for injection of the muon beam into the storage ring. The field within the inflector is designed to be nearly zero. The inflector bucks out the main dipole field, but generates little or no stray field of its own. A portion of the field that remains is the field that is generated by circulating currents in the inflector magnet superconductor. Because the magnetization field has a different structure from field generated by the transport current, the magnetization field can adversely affect the field quality within the muon storage ring good field region. Correction of the effects of inflector superconductor magnetization and its effect on the good field region in the storage ring is discussed

In-gap bound states induced by interstitial Fe impurities in iron-based superconductors

Energy Technology Data Exchange (ETDEWEB)

Zhang, Degang, E-mail: degangzhang@yahoo.com

2015-12-15

Highlights: • We provide an explanation for the interesting STM observation of the robust zero energy bound state on the interstitial Fe impurities in iron-based superconductors. - Abstract: Based on a two-orbit four-band tight binding model, we investigate the low-lying electronic states around the interstitial excess Fe ions in the iron-based superconductors by using T-matrix approach. It is shown that the local density of states at the interstitial Fe impurity (IFI) possesses a strong resonance inside the gap, which seems to be insensitive to the doping and the pairing symmetry in the Fe–Fe plane, while a single or two resonances appear at the nearest neighboring (NN) Fe sites. The location and height of the resonance peaks only depend on the hopping t and the pairing parameter Δ{sub I} between the IFI and the NN Fe sites. These in-gap resonances are originated in the Andreev’s bound states due to the quasiparticle tunneling through the IFI, leading to the change of the magnitude of the superconducting order parameter. When both t and Δ{sub I} are small, this robust zero-energy bound state near the IFI is consistent with recent scanning tunneling microscopy observations.

Negative magnetic relaxation in superconductors

Directory of Open Access Journals (Sweden)

Krasnoperov E.P.

2013-01-01

Full Text Available It was observed that the trapped magnetic moment of HTS tablets or annuli increases in time (negative relaxation if they are not completely magnetized by a pulsed magnetic field. It is shown, in the framework of the Bean critical-state model, that the radial temperature gradient appearing in tablets or annuli during a pulsed field magnetization can explain the negative magnetic relaxation in the superconductor.

Workshop on Accelerator Magnet Superconductors, Design and Optimization

CERN Document Server

WAMSDO Workshop

2009-01-01

This report contains the proceedings of the CARE-HHH-AMT Workshop on Accelerator Magnet Superconductors, Design and Optimization (WAMSDO) held at CERN from 19 to 23 May 2008. The needs in terms of superconducting magnets for the accelerator projects were discussed, mainly for the LHC interaction regions and injector upgrades, and for the GSI FAIR complex. The first part of the workshop focused on the development of superconductor and cables, i.e., low-loss Nb-Ti cables, Nb$_{3}$Sn and high-temperature superconductors. An industry session summarized the actual plans and status of the activities in the main European industries. Then, a worldwide status of the high field magnets programme was presented. A special session was devoted to fast cycled magnets, including FAIR facilities and LHC injector upgrades. A final session focused on the optimization methods and numerical tools for magnet design.

Impurity-induced states in superconducting heterostructures

Science.gov (United States)

Liu, Dong E.; Rossi, Enrico; Lutchyn, Roman M.

2018-04-01

Heterostructures allow the realization of electronic states that are difficult to obtain in isolated uniform systems. Exemplary is the case of quasi-one-dimensional heterostructures formed by a superconductor and a semiconductor with spin-orbit coupling in which Majorana zero-energy modes can be realized. We study the effect of a single impurity on the energy spectrum of superconducting heterostructures. We find that the coupling between the superconductor and the semiconductor can strongly affect the impurity-induced states and may induce additional subgap bound states that are not present in isolated uniform superconductors. For the case of quasi-one-dimensional superconductor/semiconductor heterostructures we obtain the conditions for which the low-energy impurity-induced bound states appear.

Monte Carlo method for magnetic impurities in metals

Science.gov (United States)

Hirsch, J. E.; Fye, R. M.

1986-01-01

The paper discusses a Monte Carlo algorithm to study properties of dilute magnetic alloys; the method can treat a small number of magnetic impurities interacting wiith the conduction electrons in a metal. Results for the susceptibility of a single Anderson impurity in the symmetric case show the expected universal behavior at low temperatures. Some results for two Anderson impurities are also discussed.

Stability of magnetic tip/superconductor levitation systems

International Nuclear Information System (INIS)

Alqadi, M. K.

2015-01-01

The vertical stability of a magnetic tip over a superconducting material is investigated by using the critical state and the frozen image models. The analytical expressions of the stiffness and the vibration frequency about the equilibrium position are derived in term of the geometrical parameters of the magnet/superconductor system. It is found that the stability of the system depends on the shape of the superconductor as well as its thickness. (paper)

Stress analysis in high-temperature superconductors under pulsed field magnetization

Science.gov (United States)

Wu, Haowei; Yong, Huadong; Zhou, Youhe

2018-04-01

Bulk high-temperature superconductors (HTSs) have a high critical current density and can trap a large magnetic field. When bulk superconductors are magnetized by the pulsed field magnetization (PFM) technique, they are also subjected to a large electromagnetic stress, and the resulting thermal stress may cause cracking of the superconductor due to the brittle nature of the sample. In this paper, based on the H-formulation and the law of heat transfer, we can obtain the distributions of electromagnetic field and temperature, which are in qualitative agreement with experiment. After that, based on the dynamic equilibrium equations, the mechanical response of the bulk superconductor is determined. During the PFM process, the change in temperature has a dramatic effect on the radial and hoop stresses, and the maximum radial and hoop stress are 24.2 {{MPa}} and 22.6 {{MPa}}, respectively. The mechanical responses of a superconductor for different cases are also studied, such as the peak value of the applied field and the size of bulk superconductors. Finally, the stresses are also presented for different magnetization methods.

Temperature measurement of RE123 bulk superconductors on magnetizing process

International Nuclear Information System (INIS)

Yokoyama, K.; Kaneyama, M.; Oka, T.; Fujishiro, H.; Noto, K.

2004-01-01

We study on the magnetization behavior of to magnetize RE123 bulk superconductors to apply it as strong magnets. Through magnetizing process, the temperature of bulk superconductors is raised by pinning loss caused by the magnetic fluxes motion (e.g. flux jump of flux flow), and the trapped field is decreased. This paper presents the measurement of temperature changes of Sm123 bulk superconductors during the exciting process by iteratively magnetizing pulsed-field operation with reducing amplitudes (IMRA) method. Five thermocouples are put on the surface of Sm123 bulk superconductor of 46 mm in diameter. The temperatures at the center, on the growth sector boundary (GSB) line and in the sector region surrounded by GSB's line (inter-GSB region) are monitored. The temperature at a cold stage is also measured. A Hall sensor is attached near the center thermocouple to measure the trapped field. After a bulk superconductor is cooled by the GM type refrigerator until 40 K, iterative pulsed-fields of 2.32-5.42 T are applied by a magnetizing coil. When high magnetic field of 5.42 T is applied, a temperature of bulk superconductor reaches to 72.4 K and the magnetic field distribution has C form with which a part of circle is dented, and then, a trapped field is 2.28 T. When a lower magnetic field of 4.64 T is applied, a maximum temperature is 68.3 K and a trapped field is raised to 2.70 T, and moreover, the distribution becomes round shape like field-cooling method (FC). We showed clearly that heat generation by pinning loss was related to the mechanism of magnetic field capture

A novel heat engine for magnetizing superconductors

Energy Technology Data Exchange (ETDEWEB)

Coombs, T A; Hong, Z; Zhu, X [Cambridge University Engineering Department, Trumpington Street, CB2 1PZ (United Kingdom); Krabbes, G [IFW Dresden, Helmholtzstrasse 20, 01069 Dresden (Germany)

2008-03-01

The potential of bulk melt-processed YBCO single domains to trap significant magnetic fields (Tomita and Murakami 2003 Nature 421 517-20; Fuchs et al 2000 Appl. Phys. Lett. 76 2107-9) at cryogenic temperatures makes them particularly attractive for a variety of engineering applications including superconducting magnets, magnetic bearings and motors (Coombs et al 1999 IEEE Trans. Appl. Supercond. 9 968-71; Coombs et al 2005 IEEE Trans. Appl. Supercond. 15 2312-5). It has already been shown that large fields can be obtained in single domain samples at 77 K. A range of possible applications exist in the design of high power density electric motors (Jiang et al 2006 Supercond. Sci. Technol. 19 1164-8). Before such devices can be created a major problem needs to be overcome. Even though all of these devices use a superconductor in the role of a permanent magnet and even though the superconductor can trap potentially huge magnetic fields (greater than 10 T) the problem is how to induce the magnetic fields. There are four possible known methods: (1) cooling in field; (2) zero field cooling, followed by slowly applied field; (3) pulse magnetization; (4) flux pumping. Any of these methods could be used to magnetize the superconductor and this may be done either in situ or ex situ. Ideally the superconductors are magnetized in situ. There are several reasons for this: first, if the superconductors should become demagnetized through (i) flux creep, (ii) repeatedly applied perpendicular fields (Vanderbemden et al 2007 Phys. Rev. B 75 (17)) or (iii) by loss of cooling then they may be re-magnetized without the need to disassemble the machine; secondly, there are difficulties with handling very strongly magnetized material at cryogenic temperatures when assembling the machine; thirdly, ex situ methods would require the machine to be assembled both cold and pre-magnetized and would offer significant design difficulties. Until room temperature superconductors can be prepared, the

A novel heat engine for magnetizing superconductors

International Nuclear Information System (INIS)

Coombs, T A; Hong, Z; Zhu, X; Krabbes, G

2008-01-01

The potential of bulk melt-processed YBCO single domains to trap significant magnetic fields (Tomita and Murakami 2003 Nature 421 517-20; Fuchs et al 2000 Appl. Phys. Lett. 76 2107-9) at cryogenic temperatures makes them particularly attractive for a variety of engineering applications including superconducting magnets, magnetic bearings and motors (Coombs et al 1999 IEEE Trans. Appl. Supercond. 9 968-71; Coombs et al 2005 IEEE Trans. Appl. Supercond. 15 2312-5). It has already been shown that large fields can be obtained in single domain samples at 77 K. A range of possible applications exist in the design of high power density electric motors (Jiang et al 2006 Supercond. Sci. Technol. 19 1164-8). Before such devices can be created a major problem needs to be overcome. Even though all of these devices use a superconductor in the role of a permanent magnet and even though the superconductor can trap potentially huge magnetic fields (greater than 10 T) the problem is how to induce the magnetic fields. There are four possible known methods: (1) cooling in field; (2) zero field cooling, followed by slowly applied field; (3) pulse magnetization; (4) flux pumping. Any of these methods could be used to magnetize the superconductor and this may be done either in situ or ex situ. Ideally the superconductors are magnetized in situ. There are several reasons for this: first, if the superconductors should become demagnetized through (i) flux creep, (ii) repeatedly applied perpendicular fields (Vanderbemden et al 2007 Phys. Rev. B 75 (17)) or (iii) by loss of cooling then they may be re-magnetized without the need to disassemble the machine; secondly, there are difficulties with handling very strongly magnetized material at cryogenic temperatures when assembling the machine; thirdly, ex situ methods would require the machine to be assembled both cold and pre-magnetized and would offer significant design difficulties. Until room temperature superconductors can be prepared, the

Passive superconductor: A viable method of controlling magnetization multipoles in the SSC dipole

International Nuclear Information System (INIS)

Green, M.A.

1989-02-01

At injection, the magnetization of the superconductor produces the dominant field error in the SSC dipole magnets. The field generated by magnetization currents in the superconductor is rich in higher symmetric multipoles (normal sextupole, normal decapole, and so on). Pieces of passive superconductor properly located within the bore of the dipole magnet can cancel the higher multipoles generated by the SSC dipole coils. The multipoles generated by the passive superconductor (predominantly sextupole and decapole) are controlled by the angular and radial location of the superconductor, the volume of superconductor, and the size of the superconducting filaments within the passive conductor. This paper will present the tolerances on each of these factors. The paper will show that multipole correction using passive superconductor is in general immune to the effects of temperature and magnetization decay due to flux creep, provided that dipole superconductor and the passive correction superconductor are properly specified. When combined with a lumped correction system, the passive superconductor can be a viable alternative to continuous correction coils within the SSC dipoles. 20 refs., 8 figs., 2 tabs

Passive superconductor a viable method of controlling magnetization multipoles in the SSC dipole

International Nuclear Information System (INIS)

Green, M.A.

1989-01-01

At injection, the magnetization of the superconductor produces the dominant field error in the SSC dipole magnets. The field generated by magnetization currents in the superconductor is rich in higher symmetric multipoles (normal sextupole, normal decapole, and so on). Pieces of passive superconductor properly located within the bore of the dipole magnet can cancel the higher multipoles generated by the SSC dipole coils. The multipoles generated by the passive superconductor (predominantly sextupole and decapole) are controlled by the angular and radial location of the superconductor, the volume of superconductor, and the size of the superconducting filaments within the passive conductor. This paper will present the tolerances on each of these factors. The paper will show that multipole correction using passive superconductor is in general immune to the effects of temperature and magnetization decay due to flux creep, provided that dipole superconductor and the passive correction superconductor are properly specified. When combined with a lumped correction system, the passive superconductor can be a viable alternative to continuous correction coils within the SSC dipoles. 20 refs., 8 figs., 2 tabs

Iron chalcogenide superconductors at high magnetic fields

Science.gov (United States)

Lei, Hechang; Wang, Kefeng; Hu, Rongwei; Ryu, Hyejin; Abeykoon, Milinda; Bozin, Emil S; Petrovic, Cedomir

2012-01-01

Iron chalcogenide superconductors have become one of the most investigated superconducting materials in recent years due to high upper critical fields, competing interactions and complex electronic and magnetic phase diagrams. The structural complexity, defects and atomic site occupancies significantly affect the normal and superconducting states in these compounds. In this work we review the vortex behavior, critical current density and high magnetic field pair-breaking mechanism in iron chalcogenide superconductors. We also point to relevant structural features and normal-state properties. PMID:27877518

Magnetic excitations in iron chalcogenide superconductors.

Science.gov (United States)

Kotegawa, Hisashi; Fujita, Masaki

2012-10-01

Nuclear magnetic resonance and neutron scattering experiments in iron chalcogenide superconductors are reviewed to make a survey of the magnetic excitations in FeSe, FeSe 1- x Te x and alkali-metal-doped A x Fe 2- y Se 2 ( A = K, Rb, Cs, etc). In FeSe, the intimate relationship between the spin fluctuations and superconductivity can be seen universally for the variations in the off-stoichiometry, the Co-substitution and applied pressure. The isovalent compound FeTe has a magnetic ordering with different wave vector from that of other Fe-based magnetic materials. The transition temperature T c of FeSe increases with Te substitution in FeSe 1- x Te x with small x , and decreases in the vicinity of the end member FeTe. The spin fluctuations are drastically modified by the Te substitution. In the vicinity of the end member FeTe, the low-energy part of the spin fluctuation is dominated by the wave vector of the ordered phase of FeTe; however, the reduction of T c shows that it does not support superconductivity. The presence of same wave vector as that of other Fe-based superconductors in FeSe 1- x Te x and the observation of the resonance mode demonstrate that FeSe 1- x Te x belongs to the same group as most of other Fe-based superconductors in the entire range of x , where superconductivity is mediated by the spin fluctuations whose wave vector is the same as the nesting vector between the hole pockets and the electron pockets. On the other hand, the spin fluctuations differ for alkali-metal-doped A x Fe 2- y Se 2 and FeSe or other Fe-based superconductors in their wave vector and strength in the low-energy part, most likely because of the different Fermi surfaces. The resonance mode with different wave vector suggests that A x Fe 2- y Se 2 has an exceptional superconducting symmetry among Fe-based superconductors.

Magnetic irreversibility in granular superconductors: ac susceptibility study

International Nuclear Information System (INIS)

Perez, F.; Obradors, X.; Fontcuberta, J.; Vallet, M.; Gonzalez-Calbet, J.

1991-01-01

Ac susceptibility measurements of a ceramic weak-coupled superconductor in very low ac fields (2mG, 111Hz) are reported. We present evidence for the observation of the magnetic irreversibility following a ZFC-FC thermal cycling by means of ac susceptibilty measurements. It is shown that this technique also reflect local magnetic field effects in granular superconductors, as previously suggested in microwave surface resistance and I-V characteristics. (orig.)

Probing High Temperature Superconductors with Magnetometry in Ultrahigh Magnetic Fields

Energy Technology Data Exchange (ETDEWEB)

Li, Lu [Univ. of Michigan, Ann Arbor, MI (United States)

2017-07-26

The objective of this research is to investigate the high-field magnetic properties of high temperature superconductors, materials that conduct electricity without loss. A technique known as high-resolution torque magnetometry that was developed to directly measure the magnetization of high temperature superconductors. This technique was implemented using the 65 Tesla pulsed magnetic field facility that is part of the National High Magnetic Field Laboratory at Los Alamos National Laboratory. This research addressed unanswered questions about the interplay between magnetism and superconductivity, determine the electronic structure of high temperature superconductors, and shed light on the mechanism of high temperature superconductivity and on potential applications of these materials in areas such as energy generation and power transmission. Further applications of the technology resolve the novel physical phenomena such as correlated topological insulators, and spin liquid state in quantum magnets.

Magnetic field penetration into superconductors with sharp edges

International Nuclear Information System (INIS)

Zhilichev, Yuriy N.

2003-01-01

The magnetic field and surface currents induced within a superconductor are calculated assuming the field penetrates in it near sharp corners. Rounding the corners is used to keep the field less than a critical value. Analytical formulas for a corner radius are given for a wire of the rectangular cross-section and a cylinder in the external magnetic field. A boundary integral method is used to calculate the boundary of the Meissner domain when the external field penetrates deep into the superconductor. The effect of degree of penetration on the magnetic moment of superconducting cylinders and wires is discussed

Levitation of a magnet over a flat type II superconductor

International Nuclear Information System (INIS)

Hellman, F.; Gyorgy, E.M.; Johnson, D.W. Jr.; O'Bryan, H.M.; Sherwood, R.C.

1988-01-01

Levitation of a magnet over a type II superconductor where the field at the superconductor exceeds H/sub c/ 1 is described and shown. The penetration and pinning of the flux lines in the superconductor cause the position of the magnet to be stable over a flat disk; a complete Meissner effect would make this position unstable. Furthermore, the observed dependence of the height of levitation on such variables as the thickness of the superconducting disk and the size of the magnet are consistent with a model described in this paper based on the energy cost of flux penetration through vortices and inconsistent with a Meissner effect model

Fundamental studies of superconductors using scanning magnetic imaging

Energy Technology Data Exchange (ETDEWEB)

Kirtley, J R [Center for Probing the Nanoscale, Stanford University, Stanford, CA (United States)

2010-12-01

In this review I discuss the application of scanning magnetic imaging to fundamental studies of superconductors, concentrating on three scanning magnetic microscopies-scanning SQUID microscopy (SSM), scanning Hall bar microscopy (SHM) and magnetic force microscopy (MFM). I briefly discuss the history, sensitivity, spatial resolution, invasiveness and potential future developments of each technique. I then discuss a selection of applications of these microscopies. I start with static imaging of magnetic flux: an SSM study provides deeper understanding of vortex trapping in narrow strips, which are used to reduce noise in superconducting circuitry. Studies of vortex trapping in wire lattices, clusters and arrays of rings and nanoholes show fascinating ordering effects. The cuprate high-T{sub c} superconductors are shown to have predominantly d-wave pairing symmetry by magnetic imaging of the half-integer flux quantum effect. Arrays of superconducting rings act as a physical analog for the Ising spin model, with the half-integer flux quantum effect helping to eliminate one source of disorder in antiferromagnetic arrangements of the ring moments. Tests of the interlayer tunneling model show that the condensation energy available from this mechanism cannot account for the high critical temperatures observed in the cuprates. The strong divergence in the magnetic fields of Pearl vortices allows them to be imaged using SSM, even for penetration depths of a millimeter. Unusual vortex arrangements occur in samples comparable in size to the coherence length. Spontaneous magnetization is not observed in Sr{sub 2}RuO{sub 4}, which is believed to have p{sub x} {+-} ip{sub y} pairing symmetry, although effects hundreds of times bigger than the sensitivity limits had been predicted. However, unusual flux trapping is observed in this superconductor. Finally, unusual flux arrangements are also observed in magnetic superconductors. I then turn to vortex dynamics: imaging of vortices

Fundamental studies of superconductors using scanning magnetic imaging

Science.gov (United States)

Kirtley, J. R.

2010-12-01

In this review I discuss the application of scanning magnetic imaging to fundamental studies of superconductors, concentrating on three scanning magnetic microscopies—scanning SQUID microscopy (SSM), scanning Hall bar microscopy (SHM) and magnetic force microscopy (MFM). I briefly discuss the history, sensitivity, spatial resolution, invasiveness and potential future developments of each technique. I then discuss a selection of applications of these microscopies. I start with static imaging of magnetic flux: an SSM study provides deeper understanding of vortex trapping in narrow strips, which are used to reduce noise in superconducting circuitry. Studies of vortex trapping in wire lattices, clusters and arrays of rings and nanoholes show fascinating ordering effects. The cuprate high-Tc superconductors are shown to have predominantly d-wave pairing symmetry by magnetic imaging of the half-integer flux quantum effect. Arrays of superconducting rings act as a physical analog for the Ising spin model, with the half-integer flux quantum effect helping to eliminate one source of disorder in antiferromagnetic arrangements of the ring moments. Tests of the interlayer tunneling model show that the condensation energy available from this mechanism cannot account for the high critical temperatures observed in the cuprates. The strong divergence in the magnetic fields of Pearl vortices allows them to be imaged using SSM, even for penetration depths of a millimeter. Unusual vortex arrangements occur in samples comparable in size to the coherence length. Spontaneous magnetization is not observed in Sr2RuO4, which is believed to have px ± ipy pairing symmetry, although effects hundreds of times bigger than the sensitivity limits had been predicted. However, unusual flux trapping is observed in this superconductor. Finally, unusual flux arrangements are also observed in magnetic superconductors. I then turn to vortex dynamics: imaging of vortices in rings of highly underdoped

Lateral restoring force on a magnet levitated above a superconductor

International Nuclear Information System (INIS)

Davis, L.C.

1990-01-01

The lateral restoring force on a magnet levitated above a superconductor is calculated as a function of displacement from its original position at rest using Bean's critical-state model to describe flux pinning. The force is linear for small displacements and saturates at large displacements. In the absence of edge effects the force always attracts the magnet to its original position. Thus it is a restoring force that contributes to the stability of the levitated magnet. In the case of a thick superconductor slab, the origin of the force is a magnetic dipole layer consisting of positive and negative supercurrents induced on the trailing side of the magnet. The qualitative behavior is consistent with experiments reported to date. Effects due to the finite thickness of the superconductor slab and the granular nature of high-T c materials are also considered

Impurity-generated non-Abelions

Science.gov (United States)

Simion, G.; Kazakov, A.; Rokhinson, L. P.; Wojtowicz, T.; Lyanda-Geller, Y. B.

2018-06-01

Two classes of topological superconductors and Majorana modes in condensed matter systems are known to date: one in which disorder induced by impurities strongly suppresses topological superconducting gap and is detrimental to Majorana modes, and another where Majorana fermions are protected by a disorder-robust topological superconductor gap. Observation and control of Majorana fermions and other non-Abelions often requires a symmetry of an underlying system leading to a gap in the single-particle or quasiparticle spectra. In semiconductor structures, impurities that provide charge carriers introduce states into the gap and enable conductance and proximity-induced superconductivity via the in-gap states. Thus a third class of topological superconductivity and Majorana modes emerges, in which topological superconductivity and Majorana fermions appear exclusively when impurities generate in-gap states. We show that impurity-enabled topological superconductivity is realized in a quantum Hall ferromagnet, when a helical domain wall is coupled to an s -wave superconductor. As an example of emergence of topological superconductivity in quantum Hall ferromagnets, we consider the integer quantum Hall effect in Mn-doped CdTe quantum wells. Recent experiments on transport through the quantum Hall ferromagnet domain wall in this system indicated a vital role of impurities in the conductance, but left unresolved the question whether impurities preclude generation of Majorana fermions and other non-Abelions in such systems in general. Here, solving a general quantum-mechanical problem of impurity bound states in a system of spin-orbit coupled Landau levels, we demonstrate that impurity-induced Majorana modes emerge at boundaries between topological and conventional superconducting states generated in a domain wall due to proximity to an s superconductor. We consider both short-range disorder and a smooth random potential. The phase diagram of the system is defined by

High critical magnetic field superconductor La3S4

International Nuclear Information System (INIS)

Westerholt, K.; Bach, H.; Wendemuth, R.; Methfessel, S.

1979-01-01

A report is presented on electrical conductivity, specific heat and magnetization measurements on La 3 S 4 single crystals. The results show that La 3 S 4 is a strong coupling superconductor with a BCS coherence length of 132 A. This extremely low value makes La 3 S 4 an intrinsic high critical magnetic field superconductor with a Landau-Ginsburg parameter of 20. For the temperature gradient of the upper critical magnetic field at the transition temperature values are found up to 35 kG/K. (author)

Influence of impurities on the density of states at the fermi level in the c(6x4)-C{sub 60}/Ag(1 0 0) two-dimensional superstructure

Energy Technology Data Exchange (ETDEWEB)

Vobornik, I. E-mail: ivana.vobornik@elettra.trieste.it; Avramova, I.; Giovanelli, L.; Panaccione, G.; Fujii, J.; Vobornik, S.; Cepek, C.; Sancrottti, M.; Rossi, G

2003-01-01

A number of recent results indicate that C{sub 60} films can superconduct at considerably high temperatures. The response of a material to impurities can give an information about its superconducting properties when more conventional methods for spotting superconductivity are difficult to apply. While magnetic impurities act as strong Cooper pair breakers in conventional superconductors, nonmagnetic impurities have none or negligible effect. We investigated the influence of magnetic and nonmagnetic impurities on the electronic structure of one monolayer C{sub 60} on Ag(1 0 0). Preliminary results show that the gap persists in the presence of nonmagnetic Au but it is completely suppressed in the presence of magnetic Fe, as expected for a superconductor. This result gives a support for the possible superconducting scenario in one monolayer C{sub 60} on Ag(1 0 0) and certainly requires additional experiments to be performed to assure the superconducting character of the film.

Tunneling processes into localized subgap states in superconductors

Energy Technology Data Exchange (ETDEWEB)

Ruby, Michael; Heinrich, Benjamin W.; Franke, Katharina J. [Freie Universitaet Berlin, Arnimallee 14, 14195 Berlin (Germany); Pientka, Falko; Peng, Yang; Oppen, Felix von [Freie Universitaet Berlin, Arnimallee 14, 14195 Berlin (Germany); Dahlem Center for Complex Quantum Systems, Freie Universitaet Berlin, 14195 Berlin (Germany)

2016-07-01

The Yu-Shiba-Rusinov states bound by magnetic impurities in conventional s-wave superconductors are a simple model system for probing the competition between superconducting and magnetic correlations. Shiba states can be observed in scanning tunneling spectroscopy (STS) as a pair of resonances at positive and negative bias voltages in the superconducting gap. These resonances have been interpreted in terms of single-electron tunneling into the localized sub-gap states. This requires relaxation mechanisms that depopulate the state after an initial tunneling event. Recently, theory suggests that the current can also be carried by Andreev processes which resonantly transfer a Cooper pair into the superconductor. We performed high-resolution STS experiments on single adatom Shiba states on the superconductor Pb, and provide evidence for the existence of two transport regimes. The single-electron processes dominate at large tip-sample distances and small tunneling currents, whereas Andreev processes become important at stronger tunneling. Our conclusions are based on a careful comparison of experiment and theory.

Strongly disordered superconductors

International Nuclear Information System (INIS)

Muttalib, K.A.

1982-01-01

We examine some universal effects of strong non-magnetic disorder on the electron-phonon and electron-electron interactions in a superconductor. In particular we explicitly take into account the effect of slow diffusion of electrons in a disordered medium by working in an exact impurity eigenstate representation. We find that the normal diffusion of electrons characterized by a constant diffusion coefficient does not lead to any significant correction to the electron-phonon or the effective electron-electron interactions in a superconductor. We then consider sufficiently strong disorder where Anderson localization of electrons becomes important and determine the effect of localization on the electron-electron interactions. We find that due to localization, the diffusion of electrons becomes anomalous in the sense that the diffusion coefficient becomes scale dependent. This results in an increase in the effective electron-electron interaction with increasing disorder. We propose that this provides a natural explanation for the unusual sensitivity of the transition temperature T/sub c/ of the high T/sub c/ superconductors (T/sub c/ > 10 0 K) to damage effects

Hall viscosity of a chiral two-orbital superconductor at finite temperatures

Science.gov (United States)

Yazdani-Hamid, Meghdad; Shahzamanian, Mohammad Ali

2018-06-01

The Hall viscosity known as the anti-symmetric part of the viscosity fourth-rank tensor. Such dissipationless response which appears for systems with broken time reversal symmetry. We calculate this non-dissipative quantity for a chiral two-orbital superconductor placed in a viscoelastic magnetic field using the linear response theory and apply our calculations to the putative multiband chiral superconductor Sr2RuO4. The chirality origin of a multiband superconductor arises from the interorbital coupling of the superconducting state. This feature leads to the robustness of the Hall viscosity against temperature and impurity effects. We study the temperature effect on the Hall viscosity at the one-loop approximation.

Classical impurity ion confinement in a toroidal magnetized fusion plasma.

Science.gov (United States)

Kumar, S T A; Den Hartog, D J; Caspary, K J; Magee, R M; Mirnov, V V; Chapman, B E; Craig, D; Fiksel, G; Sarff, J S

2012-03-23

High-resolution measurements of impurity ion dynamics provide first-time evidence of classical ion confinement in a toroidal, magnetically confined plasma. The density profile evolution of fully stripped carbon is measured in MST reversed-field pinch plasmas with reduced magnetic turbulence to assess Coulomb-collisional transport without the neoclassical enhancement from particle drift effects. The impurity density profile evolves to a hollow shape, consistent with the temperature screening mechanism of classical transport. Corroborating methane pellet injection experiments expose the sensitivity of the impurity particle confinement time to the residual magnetic fluctuation amplitude.

Magnetic Signals of High-Temperature Superconductor Bulk During the Levitation Force Measurement Process

Science.gov (United States)

Huang, Huan; Zheng, Jun; Qian, Nan; Che, Tong; Zheng, Botian; Jin, Liwei; Deng, Zigang

2017-05-01

In order to study the commonly neglected magnetic field information in the course of levitation force measurement process in a superconducting maglev system, a multipoint magnetic field measurement platform was employed to acquire magnetic signals of a bulk high-Tc superconductor on both the top and the bottom surface. Working conditions including field cooling (FC) and zero field cooling were investigated for these vertical down and up motions above a permanent magnet guideway performed on a HTS maglev measurement system. We have discussed the magnetic flux variation process based on the Bean model. A magnetic hysteresis effect similar to the levitation force hysteresis loop of the bulk superconductor was displayed and analyzed in this paper. What is more valuable, there exists some available magnetic flux on the top surface of the bulk superconductor, and the proportion is as high as 62.42% in the FC condition, which provides an experimental hint to design the superconductor bulk and the applied field for practical use in a more efficient way. In particular, this work reveals real-time magnetic flux variation of the bulk superconductor in the levitation application, which is the other important information in contrast to the macroscopic levitation and guidance force investigations in previous studies, and it enriches the existing research methods. The results are significant for understanding the magnetic characteristic of superconductors, and they can contribute to optimize the present HTS maglev system design.

The magnetostriction in a superconductor-magnet system under non-uniform magnetic field

Energy Technology Data Exchange (ETDEWEB)

Li, Xueyi; Jiang, Lang; Wu, Hao [Key Laboratory of Mechanics on Disaster and Environment in Western China attached to the Ministry of Education of China, Lanzhou University, Lanzhou, Gansu 730000 (China); Gao, Zhiwen, E-mail: gaozhw@lzu.edu.cn [Department of Mechanics and Engineering Science, College of Civil Engineering and Mechanics, Lanzhou University, Lanzhou, Gansu 730000 (China)

2017-03-15

Highlights: • We studied firstly magnetostriction in HTS under non-uniform magnetic field. • The superconductors may be homogeneous and nonhomogeneous. • The magnetostrictions response of the HTS is sensitive to the critical current density and amplitude of the applied magnetic field. • The magnetostriction of nonhomogeneous HTS is larger than that of homogeneous HTS. - Abstract: This paper describes a numerical model to examine the magnetostriction of bulk high-temperature superconductor (HTS) under non-uniform magnetic field in conjunction with finite element analysis. Through this model, the magnetostriction of homogeneous and nonhomogeneous HTS can be implemented under non-uniform magnetic field. Further, the effects of critical current density, applied field frequency and amplitude are also considered. The computational study can provide a fundamental mechanistic understanding the effects of non-uniform magnetic field on magnetostriction of HTS.

Distribution of local magnetic field of vortex lattice near anisotropic superconductor surface in inclined external fields

International Nuclear Information System (INIS)

Efremova, S.A.; Tsarevskij, S.L.

1997-01-01

Magnetic field distribution in a unit cell of the Abrikosov vortex lattice near the surface of monoaxial anisotropic type-ii superconductors in inclined external magnetic field has been found in the framework of London model for the cases when the symmetry axis is perpendicular and parallel to the superconductor surface interface. Distribution of local magnetic field as a function of the distance from the superconductor interface surface and external field inclination angle has been obtained. Using high-Tc superconductor Y-Ba-Cu-O by way of examples, it has been shown that the study of local magnetic field distribution function, depending on external magnetic field inclination angle towards the superconductor symmetry axis and towards the superconductor surface, can provide important data on anisotropic properties of the superconductor [ru

Correction of magnetization sextupole and decapole in a 5 centimeter bore SSC dipole using passive superconductor

International Nuclear Information System (INIS)

Green, M.A.

1991-05-01

Higher multipoles due to magnetization of the superconductor in four and five centimeter bore Superconducting Super Collider (SSC) superconducting dipole magnets have been observed. The use of passive superconductor to correct out the magnetization sextupole has been demonstrated on two dipoles built by the Lawrence Berkeley Laboratory (LBL). This reports shows how passive correction can be applied to the five centimeter SSC dipoles to remove sextupole and decapole caused by magnetization of the dipole superconductor. Two passive superconductor corrector options will be presented. The change in magnetization sextupole and decapole due to flux creep decay of the superconductor during injection can be partially compensated for using the passive superconductor. 9 refs; 5 figs

Magnetic Scaling in Superconductors

International Nuclear Information System (INIS)

Lawrie, I.D.

1997-01-01

The Ginzburg-Landau-Wilson superconductor in a magnetic field B is considered in the approximation that magnetic-field fluctuations are neglected. A formulation of perturbation theory is presented in which multiloop calculations fully retaining all Landau levels are tractable. A 2-loop calculation shows that, near the zero-field critical point, the singular part of the free energy scales as F sing ∼ |t| 2-α F(B|t| -2ν ), where ν is the coherence-length exponent emdash a result which has hitherto been assumed on purely dimensional grounds. copyright 1997 The American Physical Society

Method of plasma impurity control without magnetic divertor

International Nuclear Information System (INIS)

Schivell, J.F.

1977-06-01

A method is proposed for controlling impurity generation in a tokomak by skimming and pumping the scrape-off. This method avoids many of the complications of a magnetic divertor, such as specially configured magnetic fields, toroidal symmetry, and inefficient use of toroidal field volume. Estimates are given for operating parameters. Impurity reductions of as much as a factor of 10 should be achievable. The necessary high-capacity pump would employ either titanium gettering or cryocondensation

Magnetization hysteresis and history effects in conventional and high temperature superconductors

International Nuclear Information System (INIS)

Chaddah, P.

1990-01-01

The magnetization in hard superconductors is irreversible and history-dependent, and cannot be a priori compared with the equilibrium magnetization. These features have gained prominence in the high T c superconductors (HTSC) where the short coherence length presumably leads to intrinsic pinning. Various experimental features, first noticed in the HTSC, are explained by an extension of Bean's macroscopic model to include temperature variations and the field dependence of J c . This paper discusses recent measurements of history effects in niobium and show their similarities with other published data on HTSC. The authors also present our calculations of magnetization behaviour in hard superconductors of sample-shapes having a non-zero demagnetization factor

Controlling the flux dynamics in superconductors by nanostructured magnetic arrays

Science.gov (United States)

Kapra, Andrey

In this thesis we investigate theoretically how the critical current jc of nano-engineered mesoscopic superconducting film can be improved and how one can control the dynamics of the magnetic flux, e.g., the transition from flux-pinned to flux-flow regime, using arrays of magnetic nanostructures. In particularly we investigate: (1) Vortex transport phenomena in superconductors with deposited ferromagnetic structures on top, and the influence of the sample geometry on the critical parameters and on the vortex configurations. Changing geometry of the magnetic bars and magnetization of the bars will affect the critical current jc of the superconducting film. Such nanostructured ferromagnets strongly alter the vortex structure in its neighborhood. The influence of geometry, position and magnetization of the ferromagnet (single bar or regular lattice of the bars) on the critical parameters of the superconductor is investigated. (2) Effect of flux confinement in narrow superconducting channels with zigzag-shaped banks: the flux motion is confined in the transverse (perpendicular) direction of a diamond-cell-shape channel. The matching effect for the magnetic flux is found in the system relevantless of boundary condition. We discuss the dynamics of vortices in the samples and vortex pattern formation in the channel. We show how the inclusion of higher-Tc superconductor into the sample can lead to enhanced properties of the system. By adding an external driving force, we study the vortex dynamics. The different dynamic regimes are discussed. They allowed an effective control of magnetic flux in superconductors.

Vortex and characteristics of prestrained type-II deformable superconductors under magnetic fields

International Nuclear Information System (INIS)

Ma, Zeling; Wang, Xingzhe; Zhou, Youhe

2016-01-01

Highlights: • A numerical investigation of magnetic vortex dynamics of a deformable superconductor with prestrains is presented. • The prestrain has a remarkable influence on the magnetic vortex distribution and dynamics. • The different prestrains, i.e., pre-given compression and tension strains, result in dissimilar characteristics. • The energy density and spectrum in the deformable superconductor are demonstrated. - Abstract: Based on the time-dependent Ginzburg–Landau (TDGL) theory and the linear deformation theory, we present a numerical investigation of magnetic vortex characteristics of a type-II deformable superconductor with prestrain. The effect of prestrain on the wave function, vortex dynamics and energy density of a superconducting film is analyzed by solving the nonlinear TDGL equations in the presence of magnetic field. The results show that the prestrain has a remarkable influence on the magnetic vortex distribution and the vortex dynamics, as well as value of wave function of the superconductor. The different prestrains, i.e., pre-given compression and tension strains, result in dissimilar characteristics on a half-plane of deformable superconductor in an applied magnetic field, and the vortex distribution and entrance in a two dimensional superconducting film. The studies demonstrated that the compression prestrain may speed up the vortexes entering into the region of the superconducting film and increases the vortex number in comparison with those of free-prestrain case, while the tension prestrain shows the reversal features. The energy density and spectrum in the superconductor are further demonstrated numerically and discussed. The present investigation is an attempt to give insight into the superconductivity and electromagnetic characteristics taking into account the elastic deformation in superconductors.

Brillouin-Wigner theory of mixed-valence impurities in BCS superconductor: Tc/TcO and ΔC/ΔCO

International Nuclear Information System (INIS)

Li Jun; Gong Changde.

1986-08-01

The (lowest order) Brillouin-Wigner perturbational expansion theory is adopted to describe the mixed-valence impurities in the BCS superconductor. Two substantial quantities characterizing the superconducting state, i.e. the reduced transition temperature T c /T cO and the reduced specific heat jump ΔC/ΔC O are calculated numerically as a function of the impurity concentration x and the energy level difference E f between two 4f configurations. A comparison with the experimental data of the Th 1-x Ce x and Th 1-x U x alloy is also included with a more reasonable fitting than Kaiser's theory. (author)

Supercold technique duplicates magnetic field in second superconductor

Science.gov (United States)

Hildebrandt, A. F.

1964-01-01

A superconductor cylinder, charged with a high magnetic field, can be used to create a similar field in a larger cylinder. The uncharged cylinder is precooled, lowered into a helium dewar system, and fitted around the cylinder with the magnetic field. Magnetic flux lines pass through the two cylinders.

Magnetic pinning in superconductor-ferromagnet multilayers

International Nuclear Information System (INIS)

Bulaevskii, L. N.; Chudnovsky, E. M.; Maley, M. P.

2000-01-01

We argue that superconductor/ferromagnet multilayers of nanoscale period should exhibit strong pinning of vortices by the magnetic domain structure in magnetic fields below the coercive field when ferromagnetic layers exhibit strong perpendicular magnetic anisotropy. The estimated maximum magnetic pinning energy for single vortex in such a system is about 100 times larger than the pinning energy by columnar defects. This pinning energy may provide critical currents as high as 10 6 -10 7 A/cm 2 at high temperatures (but not very close to T c ) at least in magnetic fields below 0.1 T. (c) 2000 American Institute of Physics

Magnetic properties of high temperature superconductors and their interaction with high energy permanent magnets

International Nuclear Information System (INIS)

Agarwala, A.K.

1990-01-01

Magnetic properties of sintered samples of YBCO ceramic superconductors at various temperatures were measured using a vibrating sample magnetometer (VSM). Also, measurements of forces experienced by a well characterized rare earth-transition metal (RE-TM) permanent magnet (PM) interacting with the superconducting YBCO sample cooled in liquid nitrogen, were performed. Based upon the observed hysteretic magnetization properties of these high temperature superconductors (HTS), the HTS-PM interaction force at liquid nitrogen temperature was calculated from first principle, and finally correlated to the force measurement results. With this analysis, magnetic forces between the same HTS and PM system including the levitation as well as suspension effects at liquid-helium temperature are predicted

Surface impedance and optimum surface resistance of a superconductor with an imperfect surface

Science.gov (United States)

Gurevich, Alex; Kubo, Takayuki

2017-11-01

We calculate a low-frequency surface impedance of a dirty, s -wave superconductor with an imperfect surface incorporating either a thin layer with a reduced pairing constant or a thin, proximity-coupled normal layer. Such structures model realistic surfaces of superconducting materials which can contain oxide layers, absorbed impurities, or nonstoichiometric composition. We solved the Usadel equations self-consistently and obtained spatial distributions of the order parameter and the quasiparticle density of states which then were used to calculate a low-frequency surface resistance Rs(T ) and the magnetic penetration depth λ (T ) as functions of temperature in the limit of local London electrodynamics. It is shown that the imperfect surface in a single-band s -wave superconductor results in a nonexponential temperature dependence of Z (T ) at T ≪Tc which can mimic the behavior of multiband or d -wave superconductors. The imperfect surface and the broadening of the gap peaks in the quasiparticle density of states N (ɛ ) in the bulk give rise to a weakly temperature-dependent residual surface resistance. We show that the surface resistance can be optimized and even reduced below its value for an ideal surface by engineering N (ɛ ) at the surface using pair-breaking mechanisms, particularly by incorporating a small density of magnetic impurities or by tuning the thickness and conductivity of the normal layer and its contact resistance. The results of this work address the limit of Rs in superconductors at T ≪Tc , and the ways of engineering the optimal density of states by surface nanostructuring and impurities to reduce losses in superconducting microresonators, thin-film strip lines, and radio-frequency cavities for particle accelerators.

Enhancement of magnetic coupling between permanent magnets and bulk superconductors through iron embedding

International Nuclear Information System (INIS)

Seki, H.; Kurabayashi, H.; Suzuki, A.; Ikeda, M.; Akiyama, S.; Murakami, M.

2009-01-01

Magnetic torque can be transferred without contact through the coupling of permanent magnets (PM) and bulk superconductors (BSC). For this purpose, permanent magnets should have multiple pole configuration like NSNS. The magnitude of the transferable torque depends on the field strength and the gap between PM and BSC. It was found that the torque decays quickly with the gap. In order to enhance the strength of transferable magnetic torque, we prepared bulk Y-Ba-Cu-O superconductors for which Fe bars are embedded. Holes about 1 mm in diameter were mechanically drilled into bulk Y-Ba-Cu-O, and Fe bars about 0.9 mm in diameter were inserted followed by impregnation of Bi-Pb-Sn alloys with low melting points. The composite of Y-Ba-Cu-O and Fe bars attract magnetic fields generated from permanent magnet before cooling, and thereby magnetic coupling will be improved. We have found that the magnetic torque force can be greatly enhanced through iron embedding.

Magnetic states of single impurity in disordered environment

Directory of Open Access Journals (Sweden)

G.W. Ponedilok

2013-01-01

Full Text Available The charged and magnetic states of isolated impurities dissolved in amorphous metallic alloy are investigated. The Hamiltonian of the system under study is the generalization of Anderson impurity model. Namely, the processes of elastic and non-elastic scattering of conductive electrons on the ions of a metal and on a charged impurity are included. The configuration averaged one-particle Green's functions are obtained within Hartree-Fock approximation. A system of self-consistent equations is given for calculation of an electronic spectrum, the charged and the spin-polarized impurity states. Qualitative analysis of the effect of the metallic host structural disorder on the observed values is performed. Additional shift and broadening of virtual impurity level is caused by a structural disorder of impurity environment.

Superconductor Requirements and Characterization for High Field Accelerator Magnets

Energy Technology Data Exchange (ETDEWEB)

Barzi, E.; Zlobin, A. V.

2015-05-01

The 2014 Particle Physics Project Prioritization Panel (P5) strategic plan for U.S. High Energy Physics (HEP) endorses a continued world leadership role in superconducting magnet technology for future Energy Frontier Programs. This includes 10 to 15 T Nb₃Sn accelerator magnets for LHC upgrades and a future 100 TeV scale pp collider, and as ultimate goal that of developing magnet technologies above 20 T based on both High Temperature Superconductors (HTS) and Low Temperature Superconductors (LTS) for accelerator magnets. To achieve these objectives, a sound conductor development and characterization program is needed and is herein described. This program is intended to be conducted in close collaboration with U.S. and International labs, Universities and Industry.

Magnetic properties of heavy-fermion superconductors

International Nuclear Information System (INIS)

Rauchschwalbe, U.

1986-01-01

In the present thesis the magnetic properties of heavy-fermion superconductors are investigated. The magnetoresistance and the critical magnetic fields show a variety of anomalous phenomena. The Kondo lattices CeCu 2 Si and CeAl 3 are analysed by magnetoresistance and the field dependence of the resistivitis of UBe 13 , UPt 3 , URu 2 Si 2 and CeRu 3 Si are measured for temperatures < or approx. 1 K. (BHO)

Pair breaking and charge relaxation in superconductors

International Nuclear Information System (INIS)

Nielson, J.B.; Pethick, C.J.; Rammer, J.; Smith, H.

1982-01-01

We present a general formalism based on the quasiclassical Green's function for calculating charge imbalance in nonequilibrium superconductors. Our discussion is sufficiently general that it applies at arbitrary temperatures, and under conditions when the width of quasiparticle states are appreciable due to pair breaking processes, and when strong coupling effects are significant. As a first application we demonstrate in detail how in the limit of smallpair breaking and for a weak coupling superconductor the collision term in the formalism reduces to the one in the quasiparticle Boltzmann equation. We next treat the case of charge imbalance generated by tunnel injection, with pair breaking by phonons and magnetic impurities. Over the range of temperatures investigated exerimentally to date, the calculated charge imbalance is rather close to that evaluated using the Boltzmann equation, even if pair braeking is so strong as almost to destroy superconductivity. Finally we consider charge imbalance generated by the combined influence of a supercurrent and a temperature gradient. We give calculations for a dirty superconductor with scattering by phonons as the pair breaking mechanism, and the results give a reasonable account of the experimental data of Clarke, Fjordboge, and Lindelof. We carry out calculations for the case of impurity scattering along which are valid not only in the clean and dirty limits, but also for intermediate situations. These enable us to see how the large contribution to the charge imbalance found for energies close to the gap edge in the clean case is reduced with increasing impurity scattering

Size, Shape and Impurity Effects on Superconducting critical temperature.

Science.gov (United States)

Umeda, Masaki; Kato, Masaru; Sato, Osamu

Bulk superconductors have their own critical temperatures Tc. However, for a nano-structured superconductor, Tc depends on size and shape of the superconductor. Nishizaki showed that the high pressure torsion on bulks of Nb makes Tc higher, because the torsion makes many nano-sized fine grains in the bulks. However the high pressure torsion on bulks of V makes Tc lower, and Nishizaki discussed that the decrease of Tc is caused by impurities in the bulks of V. We studied size, shape, and impurity effects on Tc, by solving the Gor'kov equations, using the finite element method. We found that smaller and narrower superconductors show higher Tc. We found how size and shape affects Tc by studying spacial order parameter distributions and quasi-particle eigen-energies. Also we studied the impurity effects on Tc, and found that Tc decreases with increase of scattering rate by impurities. This work was supported in part of KAKENHI Grant Number JP26400367 and JP16K05460, and program for leading graduate schools of ministry of education, culture, sports, science and technology-Japan.

Magnetic pinning in superconductor-ferromagnet multilayers

Energy Technology Data Exchange (ETDEWEB)

Bulaevskii, L. N. [Department of Physics and Astronomy, CUNY Lehman College 250 Bedford Park Boulevard West, Bronx, New York 10468-1589 (United States); Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Chudnovsky, E. M. [Department of Physics and Astronomy, CUNY Lehman College, 250 Bedford Park Boulevard West, Bronx, New York 10468-1589 (United States); Maley, M. P. [Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)

2000-05-01

We argue that superconductor/ferromagnet multilayers of nanoscale period should exhibit strong pinning of vortices by the magnetic domain structure in magnetic fields below the coercive field when ferromagnetic layers exhibit strong perpendicular magnetic anisotropy. The estimated maximum magnetic pinning energy for single vortex in such a system is about 100 times larger than the pinning energy by columnar defects. This pinning energy may provide critical currents as high as 10{sup 6}-10{sup 7} A/cm{sup 2} at high temperatures (but not very close to T{sub c}) at least in magnetic fields below 0.1 T. (c) 2000 American Institute of Physics.

Macroscopic flux-creep magnetization of superconductors in applied magnetic field and local change peculiarities of their differential resistivity

International Nuclear Information System (INIS)

Romanovskii, V.R.

2003-01-01

The physical peculiarities of the flux-creep dynamics of low- and high-temperature superconductors placed in external varying magnetic field are studied. The flux-creep problem was studied for the partial penetration state. The proposed analysis was based on the macroscopic description of the flux creep by power and exponential equations of current-voltage characteristics of superconductors. It is shown that during flux creep the screening current penetrates into the superconductor at a finite velocity. Therefore, inside the superconductor a moving boundary of a magnetization region appears like in the critical state model. The time-dependent equations of screening current front have been written. However, unlike the critical state model nontrivial conditions are fulfilled at the moving boundary. They describe the smooth transition of the electromagnetic field induced by external perturbation to the undisturbed ones. A flux-creep distribution of the differential resistivity of the superconductor has been discussed. The performed analysis reveals that it monotonically decreases toward the moving boundary and depends on the magnetic ramp rate. In accordance with these flux-creep conditions the energy dissipation in the superconductors and their magnetic moment depend on the propagation law of the screening current moving boundary. The applicability of the Bean model for describing the flux-creep states is investigated

High-resolution dichroic imaging of magnetic flux distributions in superconductors with scanning x-ray microscopy

Energy Technology Data Exchange (ETDEWEB)

Ruoss, Stephen; Stahl, Claudia; Weigand, Markus; Schuetz, Gisela [Max-Planck-Institut fuer Intelligente Systeme, Stuttgart (Germany); Albrecht, Joachim [Research Institute for Innovative Surfaces, FINO, Aalen University (Germany)

2015-07-01

The penetration of magnetic flux into the high-temperature superconductor YBCO has been observed using a new high-resolution technique based on X-ray magnetic circular dichroism (XMCD). Superconductors coated with thin soft magnetic layers of CoFeB are observed in a scanning x-ray microscope providing cooling of the sample down to 83 K under the influence of external magnetic fields. Resulting electrical currents create an inhomogeneous magnetic field distribution above the superconductor which leads to a local reorientation of the ferromagnetic layer. X-ray absorption measurements with circular polarized radiation allows the analysis of the magnetic flux distribution in the superconductor via the ferromagnetic layer. In this work we present first images taken at 83K with high spatial resolution in the nanoscale.

Magnetic-flux dynamics of high-Tc superconductors in weak magnetic fields

DEFF Research Database (Denmark)

Il’ichev, E. V.; Jacobsen, Claus Schelde

1994-01-01

Aspects of magnetic-flux dynamics in different types of samples of the high-temperature superconductor YBa2Cu3Ox have been investigated in magnetic fields below 1 Oe and at 77 K. The experiments were carried out in an arrangement including a field coil, a flat sample perpendicular to the field...

In-gap quasiparticle excitations induced by non-magnetic Cu impurities in Na(Fe0.96Co0.03Cu0.01)As revealed by scanning tunnelling spectroscopy

Science.gov (United States)

Yang, Huan; Wang, Zhenyu; Fang, Delong; Deng, Qiang; Wang, Qiang-Hua; Xiang, Yuan-Yuan; Yang, Yang; Wen, Hai-Hu

2013-01-01

The origin of superconductivity in the iron pnictides remains unclear. One suggestion is that superconductivity in these materials has a magnetic origin, which would imply a sign-reversal s± pairing symmetry. Another suggests it is the result of orbital fluctuations, which would imply a sign-equal s++ pairing symmetry. There is no consensus yet which of these two distinct and contrasting pairing symmetries is the right one in iron pnictide superconductors. Here we explore the nature of the pairing symmetry in the superconducting state of Na(Fe0.97−xCo0.03Cux)As by probing the effect of scattering of Cooper pairs by non-magnetic Cu impurities. Using scanning tunnelling spectroscopy, we identify the in-gap quasiparticle states induced by the Cu impurities, showing signatures of Cooper pair breaking by these non-magnetic impurities–a process that is only consistent with s± pairing. This experiment provides strong evidence for the s± pairing. PMID:24248097

Magnetization studies in high temperature and conventional superconductors

International Nuclear Information System (INIS)

Grover, A.K.; Chaddah, P.

1991-01-01

In this paper, the authors state the contemporary view of the physical basis of a celebrated phenomenological model for hard superconductors. The authors highlight the qualitative and general predictions of this model relevant to various magnetic measurements. The authors give prescriptions to correlate data of different experiments with the predictions of the model with the intention of extracting information on material parameters, like J c (H), pinning potential, etc. These prescriptions will be illustrated with the data on both conventional and HTSC superconductors. The correlation of these data with the predictions of the model underscores the similarity in behaviour between the two classes of hard superconductors

Properties of magnetic impurities embedded into an anisotropic Heisenberg chain with spin gap

International Nuclear Information System (INIS)

Schlottmann, P.

2000-01-01

We consider a U(1)-invariant model consisting of the integrable anisotropic easy-axis Heisenberg chain of arbitrary spin S embedding an impurity of spin S'. The host chain has a spin gap for all values of S. The ground state properties and the elementary excitations of the host are studied as a function of the anisotropy and the magnetic field. The impurity is located on a link of the chain and interacts only with both neighboring sites. The coupling of the impurity to the lattice can be tuned by the impurity rapidity p 0 (usually playing the role of the Kondo coupling). The impurity model is then integrable as a function of two continuous parameters (the anisotropy and the impurity rapidity) and two discrete variables (the spins S and S'). The Bethe ansatz equations are derived and used to obtain the magnetization of the impurity. The impurity magnetization is non-universal as a function of p 0 . For small fields the impurity magnetization is determined by the spin gap and the van Hove singularity of the rapidity band. For an overcompensated impurity (S'< S) at intermediate fields there is a crossover to non-Fermi-liquid behavior remnant from the suppressed quantum critical point

High magnetic field multipoles generated by superconductor magnetization within a set of nested superconducting correction coils

International Nuclear Information System (INIS)

Green, M.A.

1990-04-01

Correction elements in colliding beam accelerators such as the SSC can be the source of undesirable higher magnetic field multipoles due to magnetization of the superconductor within the corrector. Quadrupole and sextupole correctors located within the main dipole will produce sextupole and decapole due to magnetization of the superconductor within the correction coils. Lumped nested correction coils can produce a large number of skew and normal magnetization multipoles which may have an adverse effect on a stored beam at injection into a high energy colliding beam machine such as the SSC. 6 refs., 2 figs., 2 tabs

Properties of the superconductor in accelerator dipole magnets

Science.gov (United States)

Teravest, Derk

Several aspects of the application of superconductors to high field dipole magnets for particle accelerators are discussed. The attention is focused on the 10 tesla (1 m model) magnet that is envisaged for the future Large Hadron Collider (LHC) accelerator. The basic motivation behind the study is the intention of employing superconductors to their utmost performance. An overview of practical supercomputers, their applications and their impact on high field dipole magnets used for particle accelerators, is presented. The LHC reference design for the dipole magnets is outlined. Several models were used to study the influence of a number of factors in the shape and in particular, the deviation from the shape that is due to the flux flow state. For the investigated extrinsic and intrinsic factors, a classification can be made with respect to the effect on the shape of the characteristic of a multifilamentary wire. The optimization of the coil structure for high field dipole magnets, with respect to the field quality is described. An analytical model for solid and hollow filaments, to calculate the effect of filament magnetization in the quality of the dipole field, is presented.

Permanent magnet with MgB{sub 2} bulk superconductor

Energy Technology Data Exchange (ETDEWEB)

Yamamoto, Akiyasu, E-mail: yamamoto@appchem.t.u-tokyo.ac.jp [The University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-8656 (Japan); JST-PRESTO, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012 (Japan); Ishihara, Atsushi; Tomita, Masaru [Railway Technical Research Institute, 2-8-38 Hikari, Kokubunji, Tokyo 185-8540 (Japan); Kishio, Kohji [The University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-8656 (Japan)

2014-07-21

Superconductors with persistent zero-resistance currents serve as permanent magnets for high-field applications requiring a strong and stable magnetic field, such as magnetic resonance imaging. The recent global helium shortage has quickened research into high-temperature superconductors (HTSs)—materials that can be used without conventional liquid-helium cooling to 4.2 K. Herein, we demonstrate that 40-K-class metallic HTS magnesium diboride (MgB{sub 2}) makes an excellent permanent bulk magnet, maintaining 3 T at 20 K for 1 week with an extremely high stability (<0.1 ppm/h). The magnetic field trapped in this magnet is uniformly distributed, as for single-crystalline neodymium-iron-boron. Magnetic hysteresis loop of the MgB{sub 2} permanent bulk magnet was determined. Because MgB{sub 2} is a simple-binary-line compound that does not contain rare-earth metals, polycrystalline bulk material can be industrially fabricated at low cost and with high yield to serve as strong magnets that are compatible with conventional compact cryocoolers, making MgB{sub 2} bulks promising for the next generation of Tesla-class permanent-magnet applications.

Low temperature X-ray imaging of magnetic flux patterns in high temperature superconductors

Science.gov (United States)

Stahl, Claudia; Ruoß, Stephen; Weigand, Markus; Bechtel, Michael; Schütz, Gisela; Albrecht, Joachim

2015-05-01

We present X-ray magnetic circular dichroism (XMCD) microscopy results obtained at liquid nitrogen temperatures on the high-Tc superconductor YBCO (YBa2Cu3O7-δ). The magnetic flux distribution arising from electric currents in the superconductor is detected and visualized using soft-magnetic Co40Fe40B20 (CoFeB) as sensor layer and XMCD as contrast mechanism. It has been shown that the XMCD contrast in the sensor layer directly corresponds to magnetic flux distribution of the superconductor and hence can be used to image magnetic structures in superconductors [Stahl et al., Phys. Rev. B 90, 104515 (2014)]. The existing scanning UHV X-ray microscopy setup MAXYMUS at the synchrotron BESSY II in Berlin has been upgraded for that purpose: we use a nitrogen based MMR Micro Miniature Joule-Thompson Cryostat with temperature range from 75 K to 580 K. The capability of the method is demonstrated on two different superconducting samples, an optimally doped thin film and a melt-textured block.

Cryocooler applications for high-temperature superconductor magnetic bearings

International Nuclear Information System (INIS)

Niemann, R. C.

1998-01-01

The efficiency and stability of rotational magnetic suspension systems are enhanced by the use of high-temperature superconductor (HTS) magnetic bearings. Fundamental aspects of the HTS magnetic bearings and rotational magnetic suspension are presented. HTS cooling can be by liquid cryogen bath immersion or by direct conduction, and thus there are various applications and integration issues for cryocoolers. Among the numerous cryocooler aspects to be considered are installation; operating temperature; losses; and vacuum pumping

Magnetic stripes in the UCoGe superconductor

Energy Technology Data Exchange (ETDEWEB)

Mora, Pablo de la [Departemento de Fisica, Facultad de Ciencias, Universidad Nacional Autonoma de Mexico, Apartado Postal 70-542, 04510 Mexico DF, Mexico and Institute de Investigacion en Materiales, Universidad Nacional Autonoma de Mexico, Campus Morelia (Mexico); Navarro, O, E-mail: delamora@unam.m [Instituto de Investigacion en Materiales, Universidad Nacional Autonoma de Mexico, Apartado Postal 70-360, 04510 Mexico DF (Mexico)

2009-05-01

The magnetic superconductor UCoGe is analyzed with an electronic structure package, spin-orbit coupling and intra-atomic repulsion (via Hubbard U{sub H}) were included. The possibility of an antiferromagnetic configuration is studied, but it is found to be unstable, also the non-collinear magnetization seems to be ruled out. The magnetization is given mainly by the Co-atoms with M = 0.6 mu{sub B}/f.u. The U-atoms have two magnetic moments; M = 0.07 and 0.32 mu{sub B}/f.u. arranged in an alternated planes along the b-direction forming magnetic stripes.

The interaction between the permanent magnet and ceramic superconductor with organic filler

International Nuclear Information System (INIS)

Woźny, L; Kisiel, A; Garbera, A

2016-01-01

The aim of the study was to examine the phenomenon of magnetic levitation for YBaCuO superconducting samples in pure form and with epoxy resin content of 40%. Samples of superconductors were prepared by the standard reaction in the solid state. The forces of interaction between the superconductor and neodymium permanent magnet were measured. Samples with epoxy resin fillers had significantly smaller levitation force than the sample of the sintered superconductors. This is due to a much lower content of pure superconducting material in the sample volume (about 60% of the YBaCuO). However, the obvious advantage of such samples is the possibility of preparation superconductors with complicated shapes, eg. for use in a superconducting bearings or other devices. (paper)

Quantum corral effects on competing orders and electronic states in chiral d + id or f-wave superconductors.

Science.gov (United States)

Zuo, Xian-Jun

2018-03-07

Self-consistent calculations are performed to characterize the quantum corral effects on the electronic states of chiral d + id or f-wave superconductors in this paper. A variety of spatial structures of competing orders are revealed in the presence of ferromagnetic nano-corrals, and superconducting islands are found to be absent in the case of small corrals while being seen for large corrals. Compared with the local suppression of superconductivity by a magnetic impurity inside the corral, surprisingly, an additional remarkable feature, i.e., obvious oscillations or enhancement of superconductivity around a non-magnetic impurity, is observed inside the magnetic corral. This is important in view of applications, especially in view of the demand for devices to locally produce strong superconductivity. Meanwhile, the charge density displays obvious modulations due to quantum confinement but in contrast, the spin density pattern exhibits its robustness against the corral effect. Furthermore, we explore the local density of states so as to be directly checked by experiments. We demonstrate that a magnetic corral can suppress the formation of quasi-particle bound states induced by an impurity inside the corral in the chiral d + id state while the f-wave case shows different behaviors. These results also propose a new route to make a distinction between the two competing pairing states in triangular-lattice superconductors.

Equivalent Coil Model for Computing Levitation Forces Between Permanent Magnets and High Temperatures Superconductors

International Nuclear Information System (INIS)

Cavia Santos, S.; Garcia-Tabares, L.

1998-05-01

A new simple theory has been developed for the study of levitation forces between a permanent magnet and a HTc superconductor. This theory is based on the assumption that both, the magnet and the superconductor, can be modelled by an equivalent coil placed on their surface. While the current flowing through the permanent magnet is constant, the equivalent current through the superconductor can be iether corresponding to screen the overall flux or a constant current corresponding to critical current density when the superconductor is saturated. A test facility has been designed and built for measuring levitation forces at variable approaching speeds. Comparison between theoretical and experimental measurements are presented in the report as well as a general description of the test facility. (Author)

Classical spins in superconductors

Energy Technology Data Exchange (ETDEWEB)

Shiba, H [Tokyo Univ.; Maki, K

1968-08-01

It is shown that there exists a localized excited state in the energy gap in a superconductor with a classical spin. At finite concentration localized excited states around classical spins form an impurity band. The process of growth of the impurity band and its effects on observable quantities are investigated.

Inter plane coupling and magnetic properties in a high Tc superconductor

International Nuclear Information System (INIS)

Malacarne, L.C.; Mendes, R.S.; Veroneze, P.R.

1997-01-01

We investigate if besides an increasing in T c , an interaction favoring pair tunneling reproduces some characteristic properties of the superconductors, in the presence of a magnetic field. With this objective, we use a sufficiently simple Hamiltonian which maintains the main qualitative aspects of the inter plane interaction through pairs. We also apply an functional integration method for obtaining the Landau-Ginzburg (L G) equations in presence of magnetic field. From these equations, we verify that the applied model presents the properties expected for a superconductor, e.g. magnetic flux quantization, Meissner effect and possible existence of vortex and vortex lattice

Evaluation of magnetic loss in a YBa sub 2 Cu sub 3 O sub x superconductor

CERN Document Server

Konishi, H; Futamura, M

2003-01-01

We measured the magnetic force between a YBa sub 2 Cu sub 3 O sub x (YBCO) superconductor and a Nd-Fe-B magnet while reciprocating the superconductor under the magnet. The magnetic force showed a hysteretic characteristic against the displacement of the superconductor. Magnetic loss calculated from the hysteresis curve decreased as the drive frequency increased. A mechanical model was used to analyze the characteristics of the magnetic loss. By adding the contribution of viscous force and repined flux lines to the mechanical model, we obtained good agreement between the analytical and experimental results. (author)

Acoustic emission in a superconductor (Nb-Ti) during magnetic field and current sweep

International Nuclear Information System (INIS)

Nomura, Harehiko

1980-01-01

Though superconducting magnets are indispensable in the fields of nuclear fusion, MHD power generation, high energy technology, and the trains using magnetic levitation, the safety of the magnets used for those fields is required to be fully investigated because their accumulating energy reaches up to several GJ. For this purpose, the improvement of monitoring techniques is extremely important to grasp exactly the magnetization of such large energy magnets. Although the detection of the terminal voltage of the magnets has been mainly used so far, the purpose has not yet been fulfilled because various phenomena appear in the form of noises in the terminal voltage. The authors have found the monitoring method using acoustic emission in a system completely independent from voltage observation. From this viewpoint, the experiments have been performed aiming at the generation of acoustic emission in conjunction with magnetization out of the fine structure of super-conductors, taking notice of the emitted sound frequency ranging over several hundred kHz. The results and investigation revealed that the superconductor itself emitted ultrasonic sound. It was found that the observation of this acoustic power intensity was able to monitor not only the magnetization of superconductors but also its current sweep. Since the motion of the magnetic flux is converted into the signal of acoustic field, this measuring method is less affected by noise disturbance from electromagnetic systems, and is expected to be useful for the researches on analyzing superconductor characteristics. (Wakatsuki, Y.)

Open questions in the magnetic behaviour of high-temperature superconductors

International Nuclear Information System (INIS)

Cohen, L.F.; Jensen, Henrik Jeldtoft

1997-01-01

A principally experimental review of vortex behaviour in high-temperature superconductors is presented. The reader is first introduced to the basic concepts needed to understand the magnetic properties of type II superconductors. The concepts of vortex melting, the vortex glass, vortex creep, etc are also discussed briefly. The bulk part of the review relates the theoretical predictions proposed for the vortex system in high temperature superconductors to experimental findings. The review ends with an attempt to direct the reader to those areas which still require further clarification. (author)

Competing pseudogap and impurity effects on the normal-state specific heat properties of cuprate superconductors

Science.gov (United States)

Dzhumanov, S.; Karimboev, E. X.

2014-07-01

In this paper, we show that the pseudogap in the excitation spectra of high-Tc cuprates together with the impurity phase and charge inhomogeneity plays key roles in determining the essential features of their anomalous specific heat properties observed above Tc. We consider the doped cuprate superconductor as a multi-carrier model system (which consists of intrinsic and extrinsic polarons and pre-formed bosonic Cooper pairs) and study the competing pseudogap and impurity effects on the normal-state electronic specific heat of high-Tc cuprates taking into account charge inhomogeneities. We argue that unconventional electron-phonon interactions are responsible for the precursor Cooper pairing in the polaronic band below a mean-field temperature T∗ and the existence of a pseudogap above Tc in the cuprates. The electronic specific heat Ce(T) of doped cuprates below T∗ is calculated taking into account three contributions coming from the excited components of Cooper pairs, the ideal Bose-gas of incoherent Cooper pairs and the unpaired carriers in the impurity band. Above T∗, two contributions to Ce(T) coming from the unpaired intrinsic and extrinsic polarons are calculated within the two-component degenerate Fermi-gas model. By comparing our results with the experimental Ce(T) data obtained for La- and Y-based cuprates, we find that the observed behaviors of Ce(T) (below and above T∗) are similar to the calculated results for Ce(T) and the BCS-type jumps of Ce(T) at T∗ may be depressed by the impurity effects and may become more or less pronounced BCS-type anomalies in Ce(T) .

Nuclear relaxation in semiconductors doped with magnetic impurities

International Nuclear Information System (INIS)

Mel'nichuk, S.V.; Tovstyuk, N.K.

1984-01-01

The temperature and concentration dependences are investigated of the nuclear spin-lattice relaxation time with account of spin diffusion for degenerated and non-degenerated semicon- ductors doped with magnetic impurities. In case of the non-degenerated semiconductor the time is shown to grow with temperature, while in case of degenerated semiconductor it is practically independent of temperature. The impurity concentration growth results in decreasing the spin-lattice relaxation time

Temperature factor for magnetic instability conditions of type – II superconductors

International Nuclear Information System (INIS)

Romanovskii, V.

2014-01-01

Highlights: • Electrodynamics and thermal diffusion phenomena in superconductors have the fission-chain-reaction nature. • There exist nontrivial relations between stability conditions, allowable losses and stable superconductor’s overheating. • The magnetic stability conditions are direct consequence of the states when the heat releases exceeds the critical energy. • The critical energy of magnetic instability depends on the nature of an external disturbance. • The non-isothermal magnetic instability conditions of the critical state are formulated. - Abstract: The macroscopic development of interrelated electrodynamics and thermal states taking place both before and after instability onset in type-II superconductors are studied using the critical state and the flux creep concepts. The physical mechanisms of the non-isothermal formation of the critical state are discussed solving the set of unsteady thermo-electrodynamics equations taking into consideration the unknown moving penetration boundary of the magnetic flux. To make it, the numerical method, which allows to study diffusion phenomena with unknown moving phase-two boundary, is developed. The corresponding non-isothermal flux jump criteria are written. It is proved for the first time that, first, the diffusion phenomena in superconductors have the fission-chain-reaction nature, second, the stability conditions, losses in superconductor and its stable overheating before instability onset are mutually dependent. The results are compared with those following from the existing magnetic instability theory, which does not take into consideration the stable temperature increase of superconductor before the instability onset. It is shown that errors of isothermal approximation are significant for modes closed to adiabatic ones. Therefore, the well-known adiabatic flux jump criterion limits the range of possible stable superconducting states since a correct determination of their stability states must

Optical conductivity and electronic Raman response of cuprate superconductors

International Nuclear Information System (INIS)

Vanyolos, A.; Dora, B.; Virosztek, A.

2010-01-01

We present the results of detailed analytical calculations for the in-plane optical conductivity and the electronic Raman susceptibility in quasi two-dimensional systems possessing a ground state with two competing order parameters: a d-wave density wave (dDW) and d-wave superconductor (dSC). In the coexisting dDW+dSC phase we determine the frequency dependence of these correlation functions in the presence of randomly distributed non-magnetic impurities in the unitary limit.

A superconducting conveyer system using multiple bulk Y-Ba-Cu-O superconductors and permanent magnets

Science.gov (United States)

Kinoshita, T.; Koshizuka, N.; Nagashima, K.; Murakami, M.

Developments of non-contact superconducting devices like superconducting magnetic levitation transfer and superconducting flywheel energy storage system have been performed based on the interactions between bulk Y-Ba-Cu-O superconductors and permanent magnets, in that the superconductors can stably be levitated without any active control. The performances of noncontact superconducting devices are dependent on the interaction forces like attractive forces and stiffness. In the present study, we constructed a non-contact conveyer for which the guide rails were prepared by attaching many Fe-Nd-B magnets onto an iron base plate. Along the translational direction, all the magnets were arranged as to face the same pole, and furthermore their inter-distance was made as small as possible. The guide rail has three magnet rows, for which the magnets were glued on the iron plate such that adjacent magnet rows have opposite poles like NSN. At the center row, the magnetic field at zero gap reached 0.61T, while the field strengths of two rows on the side edges were only 0.48T due to magnetic interactions among permanent magnets. We then prepared a cryogenic box made with FRP that can store several bulk Y-Ba-Cu-O superconductors 25 mm in diameter cooled by liquid nitrogen. It was found that the levitation forces and stiffness increased with increasing the number of bulk superconductors installed in the box, although the levitation force per unit bulk were almost the same. We also confirmed that these forces are dependent on the configuration of bulk superconductors.

Effect of magnetic islands on the impurity transport in a tokamak

International Nuclear Information System (INIS)

Ivanov, N.V.; Khvostenko, P.P.; Chudnovskij, A.N.

1986-01-01

Effect of magnetic islands m=2, created in plasma with the help of special quadrupole winding, on the behaviour of impurity in the T-7 tokamak is studied. The use of quadrupole winding permitted to exlude the magnetic island nonstationarity typical to spontaneous development of the Tiaring instability. The results obtained confirm the point of view that splitting of rational magnetic surface results in the change of impurity ion density gradient in its vicinity. This change occurs under the action of ambipolar electric field, that is excited due to the increase of radial electron transport in magnetic islands

The magnetic flux dynamics in the critical state of one-dimensional discrete superconductor

International Nuclear Information System (INIS)

Ginzburg, S.L.; Nakin, A.V.; Savitskaya, N.E.

2006-01-01

We give a theoretical description of avalanche-like dynamics of magnetic flux in the critical state of discrete superconductors using a one-dimensional model of a multijunction SQUID. We show that the system under consideration demonstrates the self-organized criticality. The avalanches of vortices manifest themselves as jumps of the total magnetic flux in the sample. The sizes of these jumps have a power-law distribution. We argue that similarities in the behavior of discrete and usual type-II superconductors allows to extend our results for description of avalanche-like dynamics in type-II superconductors with strong pinning

Magnetic impurity effect on charge and magnetic order in doped La1.5Ca0.5CoO4

Science.gov (United States)

Horigane, K.; Hiraka, H.; Tomiyasu, K.; Ohoyama, K.; Louca, D.; Yamada, K.

2012-02-01

Neutron scattering experiments were performed on single crystals of magnetic impurity doped cobalt oxides La1.5Ca0.5CoO4 to characterize the charge and spin orders. We newly found contrasting impurity effects. Two types of magnetic peaks are observed at q = (0.5,0,L) with L = half-integer and integer in La1.5Ca0.5CoO4, while magnetic peak at L = half-integer (integer) was only observed in Mn (Fe)-substituted sample. Although Mn and Fe impurities degrade charge and magnetic order, Cr impurity stabilizes the ordering at x = 0.5. Based on the crystal structural analysis of Cr doped sample, we found that the excess oxygen and change of octahedron around Co3+ were realized in Cr doped sample.

Superconducting Gap Symmetry of LaFeP(O,F Observed by Impurity Doping Effect

Directory of Open Access Journals (Sweden)

Shigeki Miyasaka

2016-08-01

Full Text Available We have investigated Mn, Co and Ni substitution effects on polycrystalline samples of LaFePO0.95F0.05 by resistivity and magnetoresistance measurements. In LaFe1-xMxPO0.95F0.05 (M = Mn, Co and Ni, the superconducting transition temperature (Tc monotonously decreases with increasing the impurity doping level of x. There is a clear difference of Tc suppression rates among Mn, Co and Ni doping cases, and the decreasing rate of Tc by Mn doping as a magnetic impurity is larger than those by the nonmagnetic doping impurities (Co/Ni. This result indicates that in LaFePO0.95F0.05, Tc is rapidly suppressed by the pair-breaking effect of magnetic impurities, and the pairing symmetry is a full-gapped s-wave. In the nonmagnetic impurity-doped systems, the residual resistivity in the normal state has nearly the same value when Tc becomes zero. The residual resistivity value is almost consistent with the universal value of sheet resistance for two-dimensional superconductors, suggesting that Tc is suppressed by electron localization in Co/Ni-doped LaFePO0.95F0.05.

Magnetism without magnetic impurities in ZrO.sub.2./sub. oxide

Czech Academy of Sciences Publication Activity Database

Máca, František; Kudrnovský, Josef; Drchal, Václav; Bouzerar, G.

2008-01-01

Roč. 92, č. 21 (2008), 212503/1-212503/3 ISSN 0003-6951 R&D Projects: GA ČR GA202/07/0456; GA AV ČR IAA100100616; GA MŠk OC 150 Institutional research plan: CEZ:AV0Z10100520 Keywords : magnetism * impurity * oxides * ab initio calculations Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.726, year: 2008

Magnetic flux distributions in chiral helimagnet/superconductor bilayers

Energy Technology Data Exchange (ETDEWEB)

Kato, Masaru, E-mail: kato@ms.osakafu-u.ac.jp [Department of Mathematical Sciences, Osaka Prefecture University, 1-1, Gakuencho, Nakaku, Sakai, Osaka 599-8531 (Japan); Fukui, Saoto [Department of Mathematical Sciences, Osaka Prefecture University, 1-1, Gakuencho, Nakaku, Sakai, Osaka 599-8531 (Japan); Sato, Osamu [Osaka Prefecture University College of Technology, 26-12, Saiwaicho, Neyagawa, Osaka 572-8572 (Japan); Togawa, Yoshihiko [Department of Physics and Electronics, Osaka Prefecture University, 1-1, Gakuencho, Nakaku, Sakai, Osaka 599-8531 (Japan)

2017-02-15

Highlights: • Vortex states in a chiral helimagnet/superconductor bilayer are investigated. • Vortex and anti-vortex appears depending on strength of helimagnet. • Vortex is elongated under a gradient field. • Vortices form a undulated triangular lattice. - Abstarct: Vortex states in a chiral helimagnet/superconductor bilayer are investigated numerically, using the Ginzburg–Landau equations with the finite element method. In this bilayer, effect of the chiral helimagnet on the superconductor is taken as an external field. Magnetic field distribution can be controlled by an applied field to the bilayer. It is shown that a single vortex in a gradient field is elongated along the field gradient. In zero applied field, there are up- and down vortices which are parallel or antiparallel to the z-axis, respectively. But increasing the applied field, down-vortices disappear and up-vortices form undulated triangular lattices.

Phenomenological approach to spin fluctuations in itinerant magnets and superconductors from ab initio calculations

Energy Technology Data Exchange (ETDEWEB)

Ortenzi, Luciano

2013-10-17

In this thesis I study the interplay between magnetism and superconductivity in itinerant magnets and superconductors. I do this by applying a semiphenomenological method to four representative compounds. In particular I use the discrepancies (whenever present) between density functional theory (DFT) calculations and the experiments in order to construct phenomenological models which explain the magnetic, superconducting and optical properties of four representative systems. I focus my attention on the superconducting and normal state properties of the recently discovered APt3P superconductors, on superconducting hole-doped CuBiSO, on the optical properties of LaFePO and finally on the ferromagnetic-paramagnetic transition of Ni3Al under pressure. At the end I present a new method which aims to describe the effect of spin fluctuations in itinerant magnets and superconductors that can be used to monitor the evolution of the electronic structure from non magnetic to magnetic in systems close to a quantum critical point.

Magnetic relaxation, flux pinning and critical currents in superconductors

International Nuclear Information System (INIS)

Lichtenberger, K.S.

1991-01-01

A systematic study of the magnetic flux pinning properties in superconductors has been undertaken in an attempt to understand the differences between the flux creep behavior of classical superconductors and high-temperature superconductors (HTSC's). In HTSC's, the ratio of the effective flux pinning energy to the thermal energy, U 0 /kT, is much smaller than that of conventional superconductors, often approaching unity. This results in much larger creep rates in HTSC's than in conventional superconductors. It is necessary to find suitable models that describe flux creep in both classical superconductors and HTSC's. Results show that while these two classes of materials are quantitatively very different, a single pinning barrier mode adequately describes both, within the proper region of the H-T plane. The model is applied to a variety of superconductors and the results are contrasted. Although the H-T plane appears to be very different HTSC's than for conventional superconductors, qualitatively the same physics describes both. In HTSC's, near the upper critical field there exists a relatively wide region of superconducting fluctuations, followed successively by regions of thermodynamic reversibility, thermally assisted flux, flux creep, and finally rigid flux lattice where little, if any, motion of the flux lattice occurs. All of these regions are also present in conventional superconductors, but often much more difficult, especially the irreversibility transition and the fluctuation region. The central finding of the flux creep analysis is that the region of flux creep is defined as a band in the H-T plane in which 2 ≤ U 0 /kT ≤ 100, and that the flux creep model applies best within this band

Superconductivity from magnetic elements under high pressure

International Nuclear Information System (INIS)

Shimizu, Katsuya; Amaya, Kiichi; Suzuki, Naoshi; Onuki, Yoshichika

2006-01-01

Can we expect the appearance of superconductivity from magnetic elements? In general, superconductivity occurs in nonmagnetic metal at low temperature and magnetic impurities destroy superconductivity; magnetism and superconductivity are as incompatible as oil and water. Here, we present our experimental example of superconducting elements, iron and oxygen. They are magnetic at ambient pressure, however, they become nonmagnetic under high pressure, then superconductor at low temperature. What is the driving force of the superconductivity? Our understanding in the early stages was a simple scenario that the superconductive state was obtained as a consequence of an emergence of the nonmagnetic states. In both cases, we may consider another scenario for the appearance of superconductivity; the magnetic fluctuation mechanism in the same way as unconventional superconductors

Exponential critical-state model for magnetization of hard superconductors

International Nuclear Information System (INIS)

Chen, D.; Sanchez, A.; Munoz, J.S.

1990-01-01

We have calculated the initial magnetization curves and hysteresis loops for hard type-II superconductors based on the exponential-law model, J c (H i ) =k exp(-|H i |/H 0 ), where k and H 0 are constants. After discussing the general behavior of penetrated supercurrents in an infinitely long column specimen, we define a general cross-sectional shape based on two equal circles of radius a, which can be rendered into a circle, a rectangle, or many other shapes. With increasing parameter p (=ka/H 0 ), the computed M-H curves show obvious differences with those computed from Kim's model and approach the results of a simple infinitely narrow square pulse J c (H i ). For high-T c superconductors, our results can be applied to the study of the magnetic properties and the critical-current density of single crystals, as well as to the determination of the intergranular critical-current density from magnetic measurements

A theory for the anisotropic interaction between two substitutional magnetic impurities and the magnetic anisotropic effect in dilute magnetic alloys

International Nuclear Information System (INIS)

Satter, M.A.

1990-08-01

In this paper, a formalism for studying the anisotropic interaction between two substitutional magnetic impurities and the magnetic anisotropic effect in a dilute noble metal- transition metal magnetic alloy has been developed from relativistic scattering theory. The theoretical development and the computational techniques of this formalism are based on relativistic spin-polarized scattering theory and relativistic band structure frameworks. For studying the magnetic anisotropic effect a convenient ''working'' frame of reference with its axes oriented along the fcc crystal axes is set up. This formalism is applied to study the situation for two Fe impurities in paramagnetic Au hosts. For AuFe dilute alloy, the two impurity site interaction as a function of separation is not oscillatory and the anisotropic effect is found to be less than the two site interaction itself only by an order of magnitude. Apart from the anisotropic coupling of the two impurity spins to the separation vector, for the first time, another weak anisotropic coupling to the crystal axes is also contained in the two site interaction. These anisotropic effects are the results of the relativistic spin-orbit interaction which are incorporated into the formalism. (author). 22 refs, 5 figs

Magnetic interference patterns in 0-pi superconductor/insulator/ferromagnet/superconductor Josephson junctions: Effects of asymmetry between 0 and pi regions

OpenAIRE

Kemmler, M.; Weides, M.; Goldobin, E.; Weiler, M.; Opel, M.; Goennenwein, S.T.B.; Vasenko, A.S.; Golubov, A.A.; Kohlstedt, H.; Koelle, D.; Kleiner, R.

2010-01-01

We present a detailed analysis of the dependence of the critical current I-c on an in-plane magnetic field B of 0, pi, and 0-pi superconductor-insulator-ferromagnet-superconductor Josephson junctions. I-c(B) of the 0 and the pi junction closely follows a Fraunhofer pattern, indicating a homogeneous critical current density j(c)(x). The maximum of I-c(B) is slightly shifted along the field axis, pointing to a small remanent in-plane magnetization of the F-layer along the field axis. I-c(B) of ...

Magnetic Fields above the Surface of aSuperconductor with Internal Magnetism

Energy Technology Data Exchange (ETDEWEB)

Bluhm, Hendrik; /Stanford U., Phys. Dept. /SLAC, SSRl

2007-06-26

The author presents a method for calculating the magnetic fields near a planar surface of a superconductor with a given intrinsic magnetization in the London limit. He computes solutions for various magnetic domain boundary configurations and derives relations between the spectral densities of the magnetization and the resulting field in the vacuum half space, which are useful if the magnetization can be considered as a statistical quantity and its features are too small to be resolved individually. The results are useful for analyzing and designing magnetic scanning experiments. Application to existing data from such experiments on Sr{sub 2}RuO{sub 4} show that a domain wall would have been detectable, but the magnetic field of randomly oriented small domains and small defects may have been smaller than the experimental noise level.

EDITORIAL: The electromagnetic properties of iron-based superconductors The electromagnetic properties of iron-based superconductors

Science.gov (United States)

Prozorov, Ruslan; Gurevich, Alex; Luke, Graeme

2010-05-01

cuprates, a superconducting 'dome' is formed upon doping the parent compounds, which exhibits antiferromagnetic and structural transitions at temperatures well above the superconducting critical temperature. This special section touches on several key aspects of these new iron-based superconductors. These topics include materials synthesis and basic characterization, the role of impurities and pairing symmetry, and mapping of the superconducting phase diagram as a function of chemical doping and pressure. Studies of transport, magnetic and optical properties account for a substantial portion of this special section. Particular attention is devoted to the role of magnetic excitations and the issue of the possible coexistence of magnetism and superconductivity. Attempts to understand the nature of the superconducting pairing are discussed from several angles, including tunneling spectroscopy and the London penetration depth. The vortex state is probed by magnetization, transport and neutron scattering, while the irreversible state is probed by studies of magnetic and transport critical current density.

Peculiar long-range supercurrent in superconductor-ferromagnet-superconductor junction containing a noncollinear magnetic domain in the ferromagnetic region

Energy Technology Data Exchange (ETDEWEB)

Meng, Hao, E-mail: menghao1982@shu.edu.cn [School of Physics and Telecommunication Engineering, Shaanxi University of Technology, Hanzhong 723001 (China); National Laboratory of Solid State Microstructures and Department of Physics, Nanjing University, Nanjing 210093 (China); Wu, Xiuqiang [National Laboratory of Solid State Microstructures and Department of Physics, Nanjing University, Nanjing 210093 (China); Ren, Yajie [School of Physics and Telecommunication Engineering, Shaanxi University of Technology, Hanzhong 723001 (China)

2015-01-14

We study the supercurrent in clean superconductor-ferromagnet-superconductor heterostructure containing a noncollinear magnetic domain in the ferromagnetic region. It is demonstrated that the magnetic domain can lead to a spin-flip scattering process, which reverses the spin orientations of the singlet Cooper pair and simultaneously changes the sign of the corresponding electronic momentum. If the ferromagnetic layers on both sides of magnetic domain have the same features, the long-range proximity effect will take place. That is because the singlet Cooper pair will create an exact phase-cancellation effect and gets an additional π phase shift as it passes through the entire ferromagnetic region. Then, the equal spin triplet pair only exists in the magnetic domain region and can not diffuse into the other two ferromagnetic layers. So, the supercurrent mostly arises from the singlet Cooper pairs, and the equal spin triplet pairs are not involved. This result can provide a approach for generating the long-range supercurrent.

Impurity effects on the magnetic ordering in chromium

International Nuclear Information System (INIS)

Fishman, R.S.

1992-05-01

It is well-known that impurities profoundly alter the magnetic properties of chromium. While vanadium impurities suppress the Neel temperature T N , manganese impurities enhanced T N substantially. As evidenced by neutron scattering experiments, doping with as little as 0.2% vanadium changes the transition from weakly first order to second order. Young and Sokoloff explained that the first-order transition in pure chromium is caused by a charge-density wave which is the second harmonic of the spin-density wave. By examining the subtle balance between the spin-density and charge- density wave terms in the mean-field free energy, we find that the first-order transition is destroyed when the vanadium concentration exceeds about 0.15%, in agreement with experiments

Magnetic impurity coupled to interacting conduction electrons

International Nuclear Information System (INIS)

Schork, T.

1996-01-01

We consider a magnetic impurity which interacts by hybridization with a system of weakly correlated electrons and determine the energy of the ground state by means of a 1/N f expansion. The correlations among the conduction electrons are described by a Hubbard Hamiltonian and are treated to the lowest order in the interaction strength. We find that their effect on the Kondo temperature, T K , in the Kondo limit is twofold: first, the position of the impurity level is shifted due to the reduction of charge fluctuations, which reduces T K . Secondly, the bare Kondo exchange coupling is enhanced as spin fluctuations are enlarged. In total, T K increases. Both corrections require intermediate states beyond the standard Varma-Yafet ansatz. This shows that the Hubbard interaction does not just provide quasiparticles, which hybridize with the impurity, but also renormalizes the Kondo coupling. copyright 1996 The American Physical Society

Non-Fermi-liquid behavior: Exact results for ensembles of magnetic impurities

CERN Document Server

Zvyagin, A A

2002-01-01

In this work we consider several exactly solvable models of magnetic impurities in critical quantum antiferromagnetic spin chains and multichannel Kondo impurities. Their ground state properties are studied and the finite set of nonlinear integral equations, which exactly describe the thermodynamics of the models, is constructed. We obtain several analytic low-energy expressions for the temperature, magnetic field, and frequency dependences of important characteristics of exactly solvable disordered quantum spin models and disordered multichannel Kondo impurities with essential many-body interactions. We show that the only low-energy parameter that gets renormalized is the velocity of the low-lying excitations (or the effective crossover scale connected with each impurity); the others appear to be universal. In our study several kinds of strong disorder important for experiments were used. Some of them produce low divergences in certain characteristics of our strongly disordered critical systems (compared wit...

Magnetic properties of layered superconductors

International Nuclear Information System (INIS)

Mansky, P.A.

1993-01-01

The organic superconductors (BEDT-TTF) 2 Cu(SNC) 2 and (TMTSF) 2 ClO 4 , with T c = 10K and 1.2K, have layered and highly anisotropic crystal structures. This thesis describes AC magnetic susceptibility measurements on these materials which illustrate the consequences of the discrete layered structure for the magnetic properties of the superconducting state. A DC magnetic field applied parallel to the layers of either material causes the rapid suppression of the AC screening response, and this indicates that the pinning restoring force for vortex motion parallel to the layers is anomalously weak in this orientation. This is believed to be due to the small size of the interlayer coherence length relative to the layer spacing. A simple estimate based on the energy and length scales relevant to Josephson coupled layers gives the correct order of magnitude for the pinning force. Pinning for vortices oriented perpendicular to the layers is larger by a factor of 500 for BEDT and 25 for TMTSF. When the DC field is applied at an angle to the layers, the initial suppression of the susceptibility is identical to that for a field parallel to the layers; when the field component normal to the layers exceeds a threshold, a sharp recovery of screening occurs. These observations indicate that the field initially enters the sample only in the direction parallel to the layers. The recovery of screening signals field penetration in the perpendicular direction at higher field strength, and is due to the onset of pinning by in-plane vortex cores. This magnetic open-quotes lock-inclose quotes effect is a qualitatively new behavior and is a direct consequence of weak interlayer coupling. The London penetration depth associated with interlayer currents is found to be on the order of hundreds of microns, comparable to that of a Josephson junction, and two to three orders of magnitude larger than for conventional superconductors

Study on impurity screening in stochastic magnetic boundary of the Large Helical Device

International Nuclear Information System (INIS)

Kobayashi, M.; Morita, S.; Feng, Y.

2008-10-01

The impurity transport characteristics in the scrape-off layer associated with a stochastic magnetic boundary of LHD are analyzed. The remnant islands with very small internal field line pitch in the stochastic region play a key role in reducing the impurity influx. The thermal force driven impurity influx is significantly suppressed when the perpendicular energy flux exceeds the parallel one inside the islands due to the small pitch. Application of the 3D edge transport code, EMC3-EIRENE, confirmed the impurity retention (screening) effect in the edge region. It is also found that the edge surface layers are the most effective region to retain (screen) impurities because of the flow acceleration and plasma cooling via short flux tubes. The carbon emission obtained in experiments is in good agreement with the modelling results, showing the impurity retention (screening) potential of the stochastic magnetic boundary. (author)

Topological phases in superconductor-noncollinear magnet interfaces with strong spin-orbit coupling

Energy Technology Data Exchange (ETDEWEB)

Menke, H.; Schnyder, A.P. [Max-Planck-Institut fuer Festkoerperforschung, Heisenbergstrasse 1, 70569 Stuttgart (Germany); Toews, A. [Max-Planck-Institut fuer Festkoerperforschung, Heisenbergstrasse 1, 70569 Stuttgart (Germany); Quantum Matter Institute, University of British Columbia, Vancouver, BC (Canada)

2016-07-01

Majorana fermions are predicted to emerge at interfaces between conventional s-wave superconductors and non-collinear magnets. In these heterostructures, the spin moments of the non-collinear magnet induce a low-energy band of Shiba bound states in the superconductor. Depending on the type of order of the magnet, the band structure of these bound states can be topologically nontrivial. Thus far, research has focused on systems where the influence of spin-orbit coupling can be neglected. Here, we explore the interplay between non-collinear (or non-coplanar) spin textures and Rashba-type spin-orbit interaction. This situation is realized, for example, in heterostructures between helical magnets and heavy elemental superconductors, such as Pb. Using a unitary transformation in spin space, we show that the effects of Rashba-type spin-orbit coupling are equivalent to the effects of the non-collinear spin texture of the helical magnet. We explore the topological phase diagram as a function of spin-orbit coupling, spin texture, and chemical potential, and find many interesting topological phases, such as p{sub x}-, (p{sub x} + p{sub y})-, and (p{sub x} + i p{sub y})-wave states. Conditions for the formation and the nature of Majorana edge channels are examined. Furthermore, we study the topological edge currents of these phases.

Oscillations of quantum transport through double-AB rings with magnetic impurity

International Nuclear Information System (INIS)

Gao Yingfang; Liang, J-Q

2006-01-01

We have studied the effect of impurity scattering on the quantum transport through double AB rings in the presence of spin-flipper in the middle lead in terms of one-dimensional quantum waveguide theory. The electron interacts with the impurity through the exchange interaction leading to spin-flip scattering. Transmissions in the spin-flipped and non-spin-flipped channels are calculated explicitly. It is found that the overall transmission and the conductance are distorted due to the impurity scattering. The extent of distortion not only depends on the strength of the impurity potential but also on the impurity position. Moreover, the transmission probability and the conductance are modulated by the magnetic flux, the size of the ring and the impurity potential strength as well

Magnetic field induced incommensurate resonance in cuprate superconductors

International Nuclear Information System (INIS)

Zhang Jingge; Cheng Li; Guo Huaiming; Feng Shiping

2009-01-01

The influence of a uniform external magnetic field on the dynamical spin response of cuprate superconductors in the superconducting state is studied based on the kinetic energy driven superconducting mechanism. It is shown that the magnetic scattering around low and intermediate energies is dramatically changed with a modest external magnetic field. With increasing the external magnetic field, although the incommensurate magnetic scattering from both low and high energies is rather robust, the commensurate magnetic resonance scattering peak is broadened. The part of the spin excitation dispersion seems to be an hourglass-like dispersion, which breaks down at the heavily low energy regime. The theory also predicts that the commensurate resonance scattering at zero external magnetic field is induced into the incommensurate resonance scattering by applying an external magnetic field large enough

Surface flux density distribution characteristics of bulk high-Tc superconductor in external magnetic field

International Nuclear Information System (INIS)

Torii, S.; Yuasa, K.

2004-01-01

Various magnetic levitation systems using oxide superconductors are developed as strong pinning forces are obtained in melt-processed bulk. However, the trapped flux of superconductor is moved by flux creep and fluctuating magnetic field. Therefore, to examine the internal condition of superconductor, the authors measure the dynamic surface flux density distribution of YBCO bulk. Flux density measurement system has a structure with the air-core coil and the Hall sensors. Ten Hall sensors are arranged in series. The YBCO bulk, which has 25 mm diameter and 13 mm thickness, is field cooled by liquid nitrogen. After that, magnetic field is changed by the air-core coil. This paper describes about the measured results of flux density distribution of YBCO bulk in the various frequencies of air-core coils currents

Surface flux density distribution characteristics of bulk high- Tc superconductor in external magnetic field

Science.gov (United States)

Torii, S.; Yuasa, K.

2004-10-01

Various magnetic levitation systems using oxide superconductors are developed as strong pinning forces are obtained in melt-processed bulk. However, the trapped flux of superconductor is moved by flux creep and fluctuating magnetic field. Therefore, to examine the internal condition of superconductor, the authors measure the dynamic surface flux density distribution of YBCO bulk. Flux density measurement system has a structure with the air-core coil and the Hall sensors. Ten Hall sensors are arranged in series. The YBCO bulk, which has 25 mm diameter and 13 mm thickness, is field cooled by liquid nitrogen. After that, magnetic field is changed by the air-core coil. This paper describes about the measured results of flux density distribution of YBCO bulk in the various frequencies of air-core coils currents.

Localized magnetic excitations for a line of magnetic impurities in a transverse Ising thin film ferromagnet

International Nuclear Information System (INIS)

Leite, R.V.; Oliveira Filho, L.O. de; Milton Pereira, J.; Cottam, M.G.; Costa Filho, R.N.

2009-01-01

A Green's function method is used to obtain the spectrum of spin excitations associated with a linear array of magnetic impurities implanted in a ferromagnetic thin film. The equations of motion for the Green's functions of the anisotropic film are written in the framework of the Ising model in a transverse field. The frequencies of localized modes are calculated as a function of the interaction parameters for the exchange coupling between impurity-spin pairs, host-spin pairs, and impurity-host neighbors, as well as the effective field parameter at the impurity sites.

Two classes of superconductors discovered in our material research: Iron-based high temperature superconductor and electride superconductor

International Nuclear Information System (INIS)

Hosono, Hideo

2009-01-01

We discovered two new classes of superconductors in the course of material exploration for electronic-active oxides. One is 12CaO . 7Al 2 O 3 crystal in which electrons accomodate in the crystallographic sub-nanometer-sized cavities. This material exhibiting metal-superconductor transition at 0.2 K is the first electride superconductor. The other is iron oxypnicitides with a layered structure. This superconductor is rather different from high T c cuprates in several respects. The high T c is emerged by doping carriers to the metallic parent phases which undergo crystallographic transition (tetra to ortho) and Pauli para to antiferromagnetic transition at ∼150 K. The T c is robust to impurity doping to the Fe sites or is induced by partial substitution of the Fe 2+ sites with Co 2+ or Ni 2+ . This article gives a brief summary of these discoveries and recent advances.

A model of magnetic impurities within the Josephson junction of a phase qubit

Energy Technology Data Exchange (ETDEWEB)

Erickson, R P; Pappas, D P [National Institute of Standards and Technology, Boulder, CO 80305 (United States)

2010-02-15

We consider a superconducting phase qubit consisting of a monocrystalline sapphire Josephson junction with its symmetry axis perpendicular to the junction interfaces. Via the London gauge, we present a theoretical model of Fe{sup 3+} magnetic impurities within the junction that describes the effect of a low concentration of such impurities on the operation of the qubit. Specifically, we derive an interaction Hamiltonian expressed in terms of angular momentum states of magnetic impurities and low-lying oscillator states of a current-biased phase qubit. We discuss the coupling between the qubit and impurities within the model near resonance. When the junction is biased at an optimal point for acting as a phase qubit, with a phase difference of {pi}/2 and impurity concentration no greater than 0.05%, we find only a slight decrease in the Q factor of less than 0.01%.

Higher magnetic field multipoles generated by superconductor magnetization within a set of nested superconducting correction coils

International Nuclear Information System (INIS)

Green, M.A.

1990-01-01

Correction elements in colliding beam accelerators such as the Superconducting Super Collider (SSC) can be the source of undesirable higher magnetic field multipoles due to magnetization of the superconductor within the corrector. Quadrupole and sextupole correctors located within the main dipole will produce sextupole and decapole due to magnetization of the superconductor within the correction coils. Lumped nested correction coils can produce a large number of skew and normal magnetization multipoles which may have an adverse effect on a stored beam at injection into a high energy colliding beam machine such as the SSC. Multipole magnetization field components have been measured within the HERA storage ring dipole magnets. Calculations of these components using the SCMAG04 code, which agree substantially with the measured multipoles, are presented in the report. As a result, in the proposed continuous correction winding for the SSC, dipoles have been replaced with lumped correction elements every six dipole magnets (about 120 meters apart). Nested lumped correction elements will also produce undesirable higher magnetization multipoles. This report shows a method by which the higher multipole generated by nested correction elements can be identified. (author)

Investigation Effects of Magnetetic Impurity Doping on Average Magnetization of Semiconducting Carbon Nanotubes

Directory of Open Access Journals (Sweden)

Saeedeh Ghafourian

2011-01-01

Full Text Available Single wall carbon nanotubes (SWCNT extensively are attractive from both theoretical and experimental point of view, due to its technological applications such as nano electronics devises. SWCNT are created by rolling a graphen sheet into a cyclindrical form. We have investigated the possibility of making a ferromagnetic semiconductor zigzag SWCNT by doping magnetic impurities. We found by increasing magnetic impurities doping on a zigzag SWCNT, average magnetization is increased and one can make a ferromagnetic semiconductor

Properties of a magnetic superconductor with weak magnetization-application to ErNi2B2C

International Nuclear Information System (INIS)

Ng, T.K.; Leung, W.T.

2001-01-01

Using a Ginsburg-Landau free-energy functional, we study the H-T phase diagram of a weak magnetic superconductor, where the magnetization from the magnetic component is marginal in supporting a spontaneous vortex phase. In particular, the competition between the spiral state and spontaneous vortex phase is analysed. Our theory is applied to understand the magnetic properties of ErNi 2 B 2 C. (orig.)

Instability in the magnetic field penetration in type II superconductors

International Nuclear Information System (INIS)

Oliveira, Isaías G. de

2015-01-01

Under the view of the time-dependent Ginzburg–Landau theory we have investigated the penetration of the magnetic field in the type II superconductors. We show that the single vortices, situated along the borderline, between the normal region channel and the superconducting region, can escape to regions still empty of vortices. We show that the origin of this process is the repulsive nature of vortex–vortex interaction, in addition to the non-homogeneous distribution of the vortices along the normal region channel. Using London theory we explain the extra gain of kinetic energy by the vortices situated along this borderline. - Highlights: • TDGL is used to study the magnetic field penetration in type II superconductors. • Instability process is found during the magnetic field penetration. • Vortices along the front of the normal region escape to superconducting region. • We explain the extra-gain of kinetic energy by vortices along the borderline

Antimagnets: controlling magnetic fields with superconductor-metamaterial hybrids

International Nuclear Information System (INIS)

Sanchez, Alvaro; Navau, Carles; Prat-Camps, Jordi; Chen Duxing

2011-01-01

Magnetism is very important in various areas of science and technology, ranging from magnetic recording through energy generation to trapping cold atoms. Physicists have managed to master magnetism-to create and manipulate magnetic fields-almost at will. Surprisingly, there is at least one property that has been elusive until now: how to 'switch off' the magnetic interaction of a magnetic material with existing magnetic fields without modifying them. Here we introduce the antimagnet, a design that conceals the magnetic response of a given volume from its exterior, without altering the external magnetic fields, in some respects analogous to recent theoretical proposals for cloaking electromagnetic waves with metamaterials. However, unlike these devices, which require extreme material properties, our device is feasible and needs only two kinds of available materials: superconductors and isotropic magnetic materials. Antimagnets may have applications in magnetic-based medical techniques such as magnetic resonance imaging or in reducing the magnetic signature of vessels or planes.

Magnetic-field dependence of impurity-induced muon depolarization in noble metals

International Nuclear Information System (INIS)

Schillaci, M.E.; Heffner, R.H.; Hutson, R.L.; Leon, M.; Cooke, D.W.; Dodds, S.A.; Richards, P.M.; MacLaughlin, D.E.; Boekema, C.

1983-01-01

We have measured the magnetic-field dependence of the muon depolarization rate up to 5 kOe in AuGd (350 ppM), AgGd (340 ppM) and AgEr (300 ppM). A simple model which includes both dipolar and nearest-neighbor contact interactions between the muon and the magnetic impurity does not fit the data. An axial crystal-field interaction, arising from the electric-field gradient induced by the muon at the site of the impurity, is found to dominate the Hamiltonian, and may have a large effect on the field dependence

Magnetic field dependence of impurity-induced muon depolarization in noble metals

Energy Technology Data Exchange (ETDEWEB)

Schillaci, M.E.; Heffner, R.H.; Hutson, R.L.; Leon, M.; Cooke, D.W.; Yaouanc, A. (Los Alamos National Lab., NM (USA)); Dodds, S.A. (Rice Univ., Houston, TX (USA). Dept. of Physics); Richards, P.M. (Sandia National Labs., Albuquerque, NM (USA)); MacLaughlin, D.E. (California Univ., Riverside (USA)); Boekema, C. (Texas Tech Univ., Lubbock (USA))

1984-01-01

The authors have measured the magnetic field dependence of the muon depolarization rate up to 5 kOe in AuGd (350 ppm), AgGd (340 ppm) and AgEr (300 ppm). A simple model which includes both dipolar and nearest-neighbor contact interactions between the muon and the magnetic impurity does not fit the data. An axial crystal-field interaction, arising from the electric field gradient induced by the muon at the site of the impurity, is found to dominate the Hamiltonian, and may have a large effect on the field dependence.

Device for investigation of magnetic flux jumps in ribbon superconductors

International Nuclear Information System (INIS)

Andrianov, A.V.; Bashkirov, Yu.A.; Kremlev, M.G.

1986-01-01

A device for simulation of magnetic flux jumps in superconductors of conducting magnet sandwich-type windings super-applyed of a ribbon conductor is described. A superconducting magnet with a measuring cassetter are the main elements of the device. An external magnetic field is generated by a two-sectional superconducting magnet permitting to simulate the shape of the magnetic field characteristic for sandwich-type windings. Maximum radial component of the magnetic field is 2 T. Jumps of the magnetic flux are recorded by induction transducers and the magnetic field-by Hall trasducer. The effect of coating of standard metal on magnetic flux jumps in Nb 3 Sn base superconducting ribbon is considered

High temperature superconductors for fusion magnets -influence of neutron irradiation

International Nuclear Information System (INIS)

Chudy, M.; Eisterer, M.; Weber, H. W.

2010-01-01

In this work authors present the results of study of influence of neutron irradiation of high temperature superconductors for fusion magnets. High temperature superconductors (type of YBCO (Yttrium-Barium-Copper-Oxygen)) are strong candidates to be applied in the next step of fusion devices. Defects induced by fast neutrons are effective pinning centres, which can significantly improve critical current densities and reduce J c anisotropy. Due to induced lattice disorder, T c is reduced. Requirements for ITER (DEMO) are partially achieved at 64 K.

Variational method for magnetic impurities in metals: impurity pairs

Energy Technology Data Exchange (ETDEWEB)

Oles, A M [Max-Planck-Institut fuer Festkoerperforschung, Stuttgart (Germany, F.R.); Chao, K A [Linkoeping Univ. (Sweden). Dept. of Physics and Measurement Technology

1980-01-01

Applying a variational method to the generalized Wolff model, we have investigated the effect of impurity-impurity interaction on the formation of local moments in the ground state. The direct coupling between the impurities is found to be more important than the interaction between the impurities and the host conduction electrons, as far as the formation of local moments is concerned. Under certain conditions we also observe different valences on different impurities.

Switching Magnetism and Superconductivity with Spin-Polarized Current in Iron-Based Superconductor.

Science.gov (United States)

Choi, Seokhwan; Choi, Hyoung Joon; Ok, Jong Mok; Lee, Yeonghoon; Jang, Won-Jun; Lee, Alex Taekyung; Kuk, Young; Lee, SungBin; Heinrich, Andreas J; Cheong, Sang-Wook; Bang, Yunkyu; Johnston, Steven; Kim, Jun Sung; Lee, Jhinhwan

2017-12-01

We explore a new mechanism for switching magnetism and superconductivity in a magnetically frustrated iron-based superconductor using spin-polarized scanning tunneling microscopy (SPSTM). Our SPSTM study on single-crystal Sr_{2}VO_{3}FeAs shows that a spin-polarized tunneling current can switch the Fe-layer magnetism into a nontrivial C_{4} (2×2) order, which cannot be achieved by thermal excitation with an unpolarized current. Our tunneling spectroscopy study shows that the induced C_{4} (2×2) order has characteristics of plaquette antiferromagnetic order in the Fe layer and strongly suppresses superconductivity. Also, thermal agitation beyond the bulk Fe spin ordering temperature erases the C_{4} state. These results suggest a new possibility of switching local superconductivity by changing the symmetry of magnetic order with spin-polarized and unpolarized tunneling currents in iron-based superconductors.

Imaging of topological magnetic pinning in superconductor-ferrimagnet bilayer with scanning Hall microscopy

International Nuclear Information System (INIS)

Marchevsky, M; Higgins, M J; Bhattacharya, S; Fratello, V J

2011-01-01

In a superconducting film deposited on ferromagnetic substrate with perpendicular magnetic anisotropy, vortex matter is confined by the magnetic potential landscape. Using scanning Hall microscopy we visualize flux accumulation and removal in a superconductor-ferrimagnet (S/F) bilayer prepared by rf sputtering of thin niobium film on bismuth-doped rare-earth iron garnet. Penetration of the perpendicular magnetic field in the S/F bilayer follows magnetic domain boundaries and is laterally guided by the garnet magnetization component along the field direction. Upon field removal, localization of the remnant flux at the disclination points of the labyrinthine domain pattern is observed. Our experiments show evidence for strong vortex pinning due the special topology of the domain pattern. Ac magnetic imaging of the transport current distribution in the bilayer reveals complex flow paths commensurate with the magnetic domain boundaries. Topological magnetic pinning can be a useful tool for enhancement and control of critical current in thin film superconductors.

Imaging of topological magnetic pinning in superconductor-ferrimagnet bilayer with scanning Hall microscopy

Energy Technology Data Exchange (ETDEWEB)

Marchevsky, M [Department of Physics, Syracuse University, Syracuse, NY 12344 (United States); Higgins, M J [Princeton High School, Princeton, NJ 08540 (United States); Bhattacharya, S [Tata Institute of Fundamental Research, Mumbai 400 005 (India); Fratello, V J, E-mail: mmartchevskii@lbl.gov [Integrated Photonics, Inc., Hillsborough, NJ 08844 (United States)

2011-02-15

In a superconducting film deposited on ferromagnetic substrate with perpendicular magnetic anisotropy, vortex matter is confined by the magnetic potential landscape. Using scanning Hall microscopy we visualize flux accumulation and removal in a superconductor-ferrimagnet (S/F) bilayer prepared by rf sputtering of thin niobium film on bismuth-doped rare-earth iron garnet. Penetration of the perpendicular magnetic field in the S/F bilayer follows magnetic domain boundaries and is laterally guided by the garnet magnetization component along the field direction. Upon field removal, localization of the remnant flux at the disclination points of the labyrinthine domain pattern is observed. Our experiments show evidence for strong vortex pinning due the special topology of the domain pattern. Ac magnetic imaging of the transport current distribution in the bilayer reveals complex flow paths commensurate with the magnetic domain boundaries. Topological magnetic pinning can be a useful tool for enhancement and control of critical current in thin film superconductors.

Effect of the magnet insertion on the performance of a superconducting pump

International Nuclear Information System (INIS)

Kondo, M.; Inoue, K.; Koshizuka, N.; Seki, H.; Murakami, M.; Hiragushi, M.; Akiyama, S.

2014-01-01

Highlights: • Non-contact rotation is possible by using permanent magnets and superconductors. • It is necessary to rotate a superconducting pump stably for practical applications. • We placed a permanent magnet at the bottom to increase the stiffness. • Inserting permanent magnets was effective in increasing the rotational stability. - Abstract: For medical and semiconductor fabrication lines, an ultra-clean and impurity-free environment is often required. In order to realize such a contaminant-free environment, it is desirable to employ a completely non-contact rotating mechanism. Such a non-contact rotation is possible by using a combination of permanent magnets and bulk superconductors. Furthermore, it is necessary to rotate a superconducting pump stably for practical applications. With the aim of increasing the stiffness of rotational parts, we placed a permanent magnet at the bottom such that the superconductors are sandwiched by top and bottom magnets. It was confirmed that the stiffness could surely be improved by arranging lower permanent magnets

Effect of the magnet insertion on the performance of a superconducting pump

Energy Technology Data Exchange (ETDEWEB)

Kondo, M., E-mail: mb12021@shibaura-it.ac.jp [Shibaura institute of Technology, Toyosu 3-7-5, Koto-ku, Tokyo 135-8548 (Japan); Inoue, K.; Koshizuka, N. [Shibaura institute of Technology, Toyosu 3-7-5, Koto-ku, Tokyo 135-8548 (Japan); Seki, H. [Awaji Materia, Kanda ogawacho 2-3-13, Chiyoda-ku, Tokyo 101-0045 (Japan); Murakami, M. [Shibaura institute of Technology, Toyosu 3-7-5, Koto-ku, Tokyo 135-8548 (Japan); Hiragushi, M. [Seikow Chemical Engineering and Machinery Ltd., Mizudocho 4-1-31, Amagasaki, Hyogo 661-0026 (Japan); Akiyama, S. [MAG-NEO, Suwa 1-4-23, Saitama Iwatsuki-ku, Saitama 339-0007 (Japan)

2014-09-15

Highlights: • Non-contact rotation is possible by using permanent magnets and superconductors. • It is necessary to rotate a superconducting pump stably for practical applications. • We placed a permanent magnet at the bottom to increase the stiffness. • Inserting permanent magnets was effective in increasing the rotational stability. - Abstract: For medical and semiconductor fabrication lines, an ultra-clean and impurity-free environment is often required. In order to realize such a contaminant-free environment, it is desirable to employ a completely non-contact rotating mechanism. Such a non-contact rotation is possible by using a combination of permanent magnets and bulk superconductors. Furthermore, it is necessary to rotate a superconducting pump stably for practical applications. With the aim of increasing the stiffness of rotational parts, we placed a permanent magnet at the bottom such that the superconductors are sandwiched by top and bottom magnets. It was confirmed that the stiffness could surely be improved by arranging lower permanent magnets.

Investigation on stresses of superconductors under pulsed magnetic fields based on multiphysics model

International Nuclear Information System (INIS)

Yang, Xiaobin; Li, Xiuhong; He, Yafeng; Wang, Xiaojun; Xu, Bo

2017-01-01

Highlights: • The differential equation including temperature and magnetic field was derived for a long cylindrical superconductor. • Thermal stress and electromagnetic stress were studied at the same time under pulse field magnetizing. • The distributions of the magnetic field, the temperature and stresses are studied and compared for two pulse fields of the different duration. • The Role thermal stress and electromagnetic stress play in the process of pulse field magnetizing is discussed. - Abstract: A multiphysics model for the numerical computation of stresses, trapped field and temperature distribution of a infinite long superconducting cylinder is proposed, based on which the stresses, including the thermal stresses and mechanical stresses due to Lorentz force, and trapped fields in the superconductor subjected to pulsed magnetic fields are analyzed. By comparing the results under pulsed magnetic fields with different pulse durations, it is found that the both the mechanical stress due to the electromagnetic force and the thermal stress due to temperature gradient contribute to the total stress level in the superconductor. For pulsed magnetic field with short durations, the thermal stress is the dominant contribution to the total stress, because the heat generated by AC-loss builds up significant temperature gradient in such short durations. However, for a pulsed field with a long duration the gradient of temperature and flux, as well as the maximal tensile stress, are much smaller. And the results of this paper is meaningful for the design and manufacture of superconducting permanent magnets.

Investigation on stresses of superconductors under pulsed magnetic fields based on multiphysics model

Energy Technology Data Exchange (ETDEWEB)

Yang, Xiaobin, E-mail: yangxb@lzu.edu.cn; Li, Xiuhong; He, Yafeng; Wang, Xiaojun; Xu, Bo

2017-04-15

Highlights: • The differential equation including temperature and magnetic field was derived for a long cylindrical superconductor. • Thermal stress and electromagnetic stress were studied at the same time under pulse field magnetizing. • The distributions of the magnetic field, the temperature and stresses are studied and compared for two pulse fields of the different duration. • The Role thermal stress and electromagnetic stress play in the process of pulse field magnetizing is discussed. - Abstract: A multiphysics model for the numerical computation of stresses, trapped field and temperature distribution of a infinite long superconducting cylinder is proposed, based on which the stresses, including the thermal stresses and mechanical stresses due to Lorentz force, and trapped fields in the superconductor subjected to pulsed magnetic fields are analyzed. By comparing the results under pulsed magnetic fields with different pulse durations, it is found that the both the mechanical stress due to the electromagnetic force and the thermal stress due to temperature gradient contribute to the total stress level in the superconductor. For pulsed magnetic field with short durations, the thermal stress is the dominant contribution to the total stress, because the heat generated by AC-loss builds up significant temperature gradient in such short durations. However, for a pulsed field with a long duration the gradient of temperature and flux, as well as the maximal tensile stress, are much smaller. And the results of this paper is meaningful for the design and manufacture of superconducting permanent magnets.

Critical Current Test of Liquid Hydrogen Cooled HTC Superconductors under External Magnetic Field

OpenAIRE

Shirai, Yasuyuki; Shiotsu, Masahiro; Tatsumoto, Hideki; Kobayashi, Hiroaki; Naruo, Yoshihiro; Nonaka, Satoshi; Inatani, Yoshifumi

2016-01-01

High-Tc (HTC) superconductors including MgB2 will show excellent properties under temperature of Liquid Hydrogen (LH2:20K), which has large latent heat and low viscosity coefficient. In order to design and fabricate the LH2 cooled superconducting energy devices, we must clear the cooling property of LH2 for superconductors, the cooling system and safety design of LH2 cooled superconducting devices and electro-magnetic property evaluation of superconductors (BSCCO, REBCO and MgB2) and their ma...

Effects of magnetic field on the cuprate high-Tc superconductor La2-xSrxCuO4

DEFF Research Database (Denmark)

Lake, B.; Aeppli, G.; Christensen, N.B.

2004-01-01

This article discusses neutron scattering measurements on the cuprate, high transition temperature superconductor La2-xSrxCuO4 (LSCO) in an applied magnetic field. LSCO is a type-II superconductor and magnetic flux can penetrate the material via the formation of vorticies. Phase coherent...

Static Magnetic Cloak without a Superconductor

Science.gov (United States)

Jiang, Wei; Ma, Yungui; He, Sailing

2018-05-01

Similar to its electromagnetic counterpart, magnetic cloaking also has very important technological applications. However, the traditional method to build a static magnetic cloak requires the use of superconducting materials as the diamagnetic component, which seriously limits the practical potential because of the cryogenic condition. We show that a diamagnetic active current boundary combined with a high-permeability magnetic inner shell (MIS) can be designed to solve this problem, rendering an ideal magnetic cloaking effect at zero frequency. We first theoretically prove that a current boundary could magnetically behave as a superconductor to external observers. Based on this phenomena, we introduce a high-permeability MIS made of magnetically ultrasoft metallic sheets (permeability μ >103 ) and experimentally prove that the bilayer combination can exactly balance out the disturbance to the external probing field and, meanwhile, have a large invisible inner space. We also show that the active boundary currents can be accordingly configured to overcome the permeability and frequency band limits, leading to a robust cloak over the entire quasistatic frequency region. Our work creates an efficient way to circumvent the traditional limits of metamaterials to build magnetic cloaks for ultralow frequencies. The active-passive hybrid approach could be generally extended to yield other artificial magnetic devices or systems as well.

Comparison of simulation and experiment on levitation force between GdBCO bulk superconductor and superconducting magnet

Energy Technology Data Exchange (ETDEWEB)

Araki, S., E-mail: satoshi@sum.sd.keio.ac.j [Department of System Design Engineering, Faculty of Science and Technology, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama 223-8522 (Japan); Nagashima, K.; Seino, H. [Railway Technical Research Institute, 2-8-38 Hikari-cho, Kokubunji, Tokyo 185-8540 (Japan); Murakami, T.; Sawa, K. [Department of System Design Engineering, Faculty of Science and Technology, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama 223-8522 (Japan)

2009-10-15

High temperature bulk superconductors have significant potential for various engineering applications such as a flywheel energy storage system. This system is expected to decrease the energy loss by using bulk superconductors for the bearing. Recently, the authors have developed a new superconducting magnet to realize large levitation force. In this system, the axial component of magnetic field is canceled each other but the radial component of magnetic field expects to be enhanced. Thus, it was expected that the large levitation force can be realized and its time relaxation will be decreased. And in the previous paper, the levitation force and its time relaxation were measured under the various conditions by using this new magnet. But it is difficult to consider what phenomenon has happened in the bulk from only experimental results. In addition the quantitative evaluation cannot be done only by the experimental results, for example, the influence of the magnetic field penetration and magnetic distribution around a bulk superconductor on the maximum force and so on. Thus, in this paper, the authors simulated the levitation force of bulk superconductor by using ELF/MAGIC, which is a three-dimensional electromagnetic analytical software. In the simulation the bulk was considered as a rigid body and the simulation was executed under the same conditions and model with the experiment. The distribution of magnetic field and the levitation force were obtained and discussed.

Comparison of simulation and experiment on levitation force between GdBCO bulk superconductor and superconducting magnet

International Nuclear Information System (INIS)

Araki, S.; Nagashima, K.; Seino, H.; Murakami, T.; Sawa, K.

2009-01-01

High temperature bulk superconductors have significant potential for various engineering applications such as a flywheel energy storage system. This system is expected to decrease the energy loss by using bulk superconductors for the bearing. Recently, the authors have developed a new superconducting magnet to realize large levitation force. In this system, the axial component of magnetic field is canceled each other but the radial component of magnetic field expects to be enhanced. Thus, it was expected that the large levitation force can be realized and its time relaxation will be decreased. And in the previous paper, the levitation force and its time relaxation were measured under the various conditions by using this new magnet. But it is difficult to consider what phenomenon has happened in the bulk from only experimental results. In addition the quantitative evaluation cannot be done only by the experimental results, for example, the influence of the magnetic field penetration and magnetic distribution around a bulk superconductor on the maximum force and so on. Thus, in this paper, the authors simulated the levitation force of bulk superconductor by using ELF/MAGIC, which is a three-dimensional electromagnetic analytical software. In the simulation the bulk was considered as a rigid body and the simulation was executed under the same conditions and model with the experiment. The distribution of magnetic field and the levitation force were obtained and discussed.

Thermal conductivity of a quantum spin-1/2 antiferromagnetic chain with magnetic impurities

International Nuclear Information System (INIS)

Zviagin, A.A.

2008-01-01

We present an exact theory that describes how magnetic impurities change the behavior of the thermal conductivity for the integrable Heisenberg antiferromagnetic quantum spin-1/2 chain. Single magnetic impurities and a large concentration of impurities with similar values of the couplings to the host chain (a weak disorder) do not change the linear-in-temperature low-T behavior of the thermal conductivity: Only the slope of that behavior becomes smaller, compared to the homogeneous case. The strong disorder in the distribution of the impurity-host couplings produces more rapid temperature growth of the thermal conductivity, compared to the linear-in-T dependence of the homogeneous chain and the chain with weak disorder. Recent experiments on the thermal conductivity in inhomogeneous quasi-one-dimensional quantum spin systems manifest qualitative agreement with our results

Flux Trapping Properties of Bulk HIGH-TC Superconductors in Static Field-Cooling Magnetization

Science.gov (United States)

Deng, Z.; Tsuzuki, K.; Miki, M.; Felder, B.; Hara, S.; Izumi, M.

2013-06-01

The trapping process and saturation effect of trapped magnetic flux of bulk high-temperature superconductors by static field-cooling magnetization (FCM) are reported in the paper. With a cryogenic Bell Hall sensor attached on the center of the bulk surface, the synchronous magnetic signals were recorded during the whole magnetization process. It enables us to know the flux trapping behavior since the removal of the excitation field, as well as the subsequent flux relaxation phenomenon and the flux dissipation in the quench process of the bulk sample. With the help of flux mapping techniques, the relationship between the trapped flux and the applied field was further investigated; the saturation effect of trapped flux was discussed by comparing the peak trapped field and total magnetic flux of the bulk sample. These studies are useful to understand the basic flux trapping properties of bulk superconductors.

Magnetic levitation on a type-I superconductor as a practical demonstration experiment for students

International Nuclear Information System (INIS)

Osorio, M R; Lahera, D E; Suderow, H

2012-01-01

We describe and discuss an experimental set-up which allows undergraduate and graduate students to view and study magnetic levitation on a type-I superconductor. The demonstration can be repeated many times using one readily available 25 l liquid helium dewar. We study the equilibrium position of a magnet that levitates over a lead bowl immersed in a liquid hand-held helium cryostat. We combine the measurement of the position of the magnet with simple analytical calculations. This provides a vivid visualization of magnetic levitation from the balance between pure flux expulsion and gravitation. The experiment contrasts and illustrates the case of magnetic levitation with high temperature type-II superconductors using liquid nitrogen, where levitation results from partial flux expulsion and vortex physics. (paper)

Magnetic levitation on a type-I superconductor as a practical demonstration experiment for students

Science.gov (United States)

Osorio, M. R.; Lahera, D. E.; Suderow, H.

2012-09-01

We describe and discuss an experimental set-up which allows undergraduate and graduate students to view and study magnetic levitation on a type-I superconductor. The demonstration can be repeated many times using one readily available 25 l liquid helium dewar. We study the equilibrium position of a magnet that levitates over a lead bowl immersed in a liquid hand-held helium cryostat. We combine the measurement of the position of the magnet with simple analytical calculations. This provides a vivid visualization of magnetic levitation from the balance between pure flux expulsion and gravitation. The experiment contrasts and illustrates the case of magnetic levitation with high temperature type-II superconductors using liquid nitrogen, where levitation results from partial flux expulsion and vortex physics.

Macroscopic quantum coherence in a magnetic nanoparticle above the surface of a superconductor

Science.gov (United States)

Chudnovsky; Friedman

2000-12-11

We study macroscopic quantum tunneling of the magnetic moment in a single-domain particle placed above the surface of a superconductor. Such a setup allows one to manipulate the height of the energy barrier, preserving the degeneracy of the ground state. The tunneling amplitude and the effect of the dissipation in the superconductor are computed.

Macroscopic Quantum Coherence in a Magnetic Nanoparticle Above the Surface of a Superconductor

Energy Technology Data Exchange (ETDEWEB)

Chudnovsky, Eugene M.; Friedman, Jonathan R.

2000-12-11

We study macroscopic quantum tunneling of the magnetic moment in a single-domain particle placed above the surface of a superconductor. Such a setup allows one to manipulate the height of the energy barrier, preserving the degeneracy of the ground state. The tunneling amplitude and the effect of the dissipation in the superconductor are computed.

Macroscopic Quantum Coherence in a Magnetic Nanoparticle Above the Surface of a Superconductor

International Nuclear Information System (INIS)

Chudnovsky, Eugene M.; Friedman, Jonathan R.

2000-01-01

We study macroscopic quantum tunneling of the magnetic moment in a single-domain particle placed above the surface of a superconductor. Such a setup allows one to manipulate the height of the energy barrier, preserving the degeneracy of the ground state. The tunneling amplitude and the effect of the dissipation in the superconductor are computed

Shape of the nuclear magnetic resonance line in anisotropic superconductors with an irregular vortex lattice

International Nuclear Information System (INIS)

Minkin, A.V.; Tsarevskij, S.L.

2006-01-01

For high-temperature superconductors the shape of a NMR spectrum line is built regarding for variation of inhomogeneity of irregular vortex lattice magnetic field near superconductor surface. It is shown that the shape of a NMR line is not simply widened but noticeably varies depending on the degree of irregularity of a superconductor vortex lattice. This variation is associated with a local symmetry decrease in an irregular vortex lattice of the superconductor. Taking into account these circumstances may considerably change conclusions about the type of a vortex lattice and superconductor parameters which are commonly gained from NMR line shape analysis [ru

Procedures for measuring the electrical properties of superconductors for accelerator magnets

International Nuclear Information System (INIS)

Sampson, W.B.

1986-01-01

There are three important electrical properties associated with the superconductor used to fabricate accelerator magnets. The most important is the critical current since this determines the performance potential of the magnet. The normal state resistivity and the volume magnetization are the other principal electrical parameters. In this report methods for measuring these parameters are presented and procedures for including self field effect and magnetoresistance are discussed

Surface flux density distribution characteristics of bulk high-T c superconductor in external magnetic field

International Nuclear Information System (INIS)

Nishikawa, H.; Torii, S.; Yuasa, K.

2005-01-01

This paper describes the measured results of the two-dimensional flux density distribution of a YBCO bulk under applied AC magnetic fields with various frequency. Melt-processed oxide superconductors have been developed in order to obtain strong pinning forces. Various electric mechanical systems or magnetic levitation systems use those superconductors. The major problem is that cracks occur because the bulk superconductors are brittle. The bulk may break in magnetizing process after cracks make superconducting state instable. The trapped flux density and the permanent current characteristics of bulk superconductors have been analyzed, so as to examine the magnetizing processes or superconducting states of the bulk. In those studies, the two-dimensional surface flux density distributions of the bulk in static fields are discussed. On the other hand, the distributions in dynamic fields are little discussed. We attempted to examine the states of the bulk in the dynamic fields, and made a unique experimental device which has movable sensors synchronized with AC applied fields. As a result, the two-dimensional distributions in the dynamic fields are acquired by recombining the one-dimensional distributions. The dynamic states of the flux of the bulk and the influences of directions of cracks are observed from the distributions. In addition, a new method for measuring two-dimensional flux density distribution under dynamic magnetic fields is suggested

Anomalous magnetic torque in the heavy-fermion superconductor UBe13

International Nuclear Information System (INIS)

Schmiedeshoff, G.M.; Fisk, Z.; Smith, J.L.

1994-01-01

Measurements of the magnetic torque acting upon a single crystal of the heavy-fermion superconductor UBe 13 have been made at temperatures from 0.5 K to 30.0 K and in magnetic fields to 23 T using a capacitive magnetometer. We find that a large, anomalous contribution to the magnetic torque appears in at low temperatures and in high fields. The anomalous torque coexists with the superconducting state at low temperature. We propose that the anomalous torque reflects the existence of a field-induced magnetic phase transition. (orig.)

Time-dependent magnetization of a type-II superconductor numerically calculated by using the flux-creep equation

International Nuclear Information System (INIS)

Lee, J. H.; Park, I. S.; Ahmad, D.; Kim, D.; Kim, Y. C.; Ko, R. K.; Jeong, D. Y.

2012-01-01

The macroscopic magnetic behaviors of a type-II superconductor, such as the field- or the temperature-dependent magnetization, have been described by using critical state models. However, because the models are time-independent, the magnetic relaxation in a type-II superconductor cannot be described by them, and the time dependence of the magnetization can affect the field or the temperature-dependent magnetization curve described by the models. In order to avoid the time independence of critical state models, we try the numerical calculation used by Qin et al., who mainly calculated the temperature dependence of the ac susceptibility χ(T). Their calculation showed that the frequency-dependent χ(T) could be obtained by using the flux-creep equation. We calculated the field-dependent magnetization and magnetic relaxation by using a numerical method. The calculated field-dependent magnetization M(H) curves shows the shapes of a typical type-II superconductor. The calculated magnetic relaxation do not show a logarithmic decay of the magnetization, but the addition of a surface barrier to the relaxation calculation caused a clear logarithmic decay of the magnetization, producing a crossover at a mid-time. This means that the logarithmic magnetic relaxation is caused by not only flux creep but also a combination of flux creep and a surface barrier.

Electronic structures and magnetic properties of 3d and 4d transition-metal impurities in ferromagnetic Fe

CERN Document Server

Park, J H; Min, B I; Cho, H S

2000-01-01

Employing the self-consistent local approach, the tight-binding linear-muffin-tin orbital recursion method, we have investigated the electronic structures and the magnetic properties of 3d and 4d transition-metal (TM) impurities in ferromagnetic bcc Fe. In both 3d and 4d TM impurities, virtual bound states appear and are characterized by a high density of states in the energy spectrum. The characters of the states are studied by calculating the bond order between interaction orbitals. For early TM impurities, the states at the impurity sites have more antibonding characters, while the states at neighboring Fe sites have more bonding characters. For late TM impurities, the situation is reversed. late TM impurities of both the 3d and the 4d TM series have the same magnetic ordering as the host Fe atoms whereas early TM impurities have magnetic moments antiparallel to that of the host. As for the Mn impurity, an inward relaxation of neighboring Fe atoms stabilizes the antiferromagnetic ordering with respect to t...

A neutron depolarization study of magnetic inhomogeneities in weak-link superconductors

International Nuclear Information System (INIS)

Zhuchenko, N.K.; Yagud, R.Z.

1993-01-01

Neutron depolarization measurements in the mixed state of both high-T c and low-T c weak-link superconductors have been carried out. Samples of YBCO, BSCCO, SnMo 6 S 8 and 0.5 Nb-0.5 Ti of different magnetic prehistory were analyzed at temperatures T 4.2 K under applied magnetic fields II <= 16.5 kOe. We ascribe the appearance of magnetic inhomogeneities and their hysteresis behaviour to the interaction between dipole magnetic fields (diamagnetic and paramagnetic ones) and applied magnetic fields

Magnetic flux periodicities and finite momentum pairing in unconventional superconductors

Energy Technology Data Exchange (ETDEWEB)

Loder, Florian

2009-12-22

This work contains a thorough study of the magnetic flux periodicity of loops of conventional and unconventional, especially d-wave, superconductors. Although already in 1961, several independent works showed that the flux period of a conventional superconducting loop is the superconducting flux quantum hc/2e, this question has never been investigated deeply for unconventional superconductors. And indeed, we show here that d-wave superconducting loops show a basic flux period of the normal flux quantum hc/e, a property originating from the nodal quasi-particle states. This doubling of the flux periodicity is best visible in the persistent current circulating in the loop, and it affects other properties of the superconductor such as the periodicity of d-wave Josephson junctions. In the second part of this work, the theory of electron pairing with finite center-of-mass momentum, necessary for the description of superconducting loops, is extended to systems in zero magnetic field. We show that even in the field free case, an unconventional pairing symmetry can lead to a superconducting ground state with finite-momentum electron pairs. Such a state has an inhomogeneous charge density and therefore is a basis for the description of coexistence of superconductivity and stripe order. (orig.)

The superconductor

International Nuclear Information System (INIS)

Lad, J.K.

1979-01-01

Techniques for fabrication of a few important superconductors like Nb, Ti and Nb 3 Sn are described. Copper or bronze or both can be used as a matrix in the superconductor. Current densities obtained for different ratios of copper to superconductor are studied. The specifications of multi-filament Nb 3 Sn superconductors are given. The relative merits of the two superconductors are discussed. The temperature range obtained is approximately 3 0 K and a magnetic field of 9T(tesla) can be achieved. (A.K.)

EDITORIAL: Focus on Iron-Based Superconductors FOCUS ON IRON-BASED SUPERCONDUCTORS

Science.gov (United States)

Hosono, Hideo; Ren, Zhi-An

2009-02-01

-L Drechsler, N Kozlova, M Bartkowiak, J E Hamann-Borrero, G Behr, K Nenkov, H-H Klauss, H Maeter, A Amato, H Luetkens, A Kwadrin, R Khasanov, J Freudenberger, A Köhler, M Knupfer, E Arushanov, H Rosner, B Büchner and L Schultz Low-energy spin dynamics in the antiferromagnetic phase of CaFe2As2 N J Curro, A P Dioguardi, N ApRoberts-Warren, A C Shockley and P Klavins Muon spin rotation study of magnetism and superconductivity in BaFe2-xCoxAs2 and Pr1-xSrxFeAsO C Bernhard, A J Drew, L Schulz, V K Malik, M Rössle, Ch Niedermayer, Th Wolf, G D Varma, G Mu, H-H Wen, H Liu, G Wu and X H Chen Magnetic impurities in the pnictide superconductor Ba1-xKxFe2As2 Sutirtha Mukhopadhyay, Sangwon Oh, A M Mounce, Moohee Lee, W P Halperin, N Ni, S L Bud'ko, P C Canfield, A P Reyes and P L Kuhns Neutron scattering investigation of the magnetic order in single crystalline BaFe2As2 M Kofu, Y Qiu, Wei Bao, S-H Lee, S Chang, T Wu, G Wu and X H Chen An NMR study on the F-doping evolution of the iron oxypnictide LaFeAs(O1-xFx) Y Nakai, S Kitagawa, K Ishida, Y Kamihara, M Hirano and H Hosono The peculiar physical properties and phase diagram of BaFe2-xCoxAs2 single crystals X F Wang, T Wu, G Wu, R H Liu, H Chen, Y L Xie and X H Chen Synthesis of LnFeAsO1-y superconductors (Ln=La and Nd) using the high-pressure technique Kiichi Miyazawa, Kunihiro Kihou, Motoyuki Ishikado, Parasharam M Shirage, Chul-Ho Lee, Nao Takeshita, Hiroshi Eisaki, Hijiri Kito and Akira Iyo Correlation effects in the iron pnictides Qimiao Si, Elihu Abrahams, Jianhui Dai and Jian-Xin Zhu Competition/coexisitence of magnetism and superconductivity in iron pnictides probed by muon spin rotation Soshi Takeshita and Ryosuke Kadono Impurity-induced in-gap state and Tc in sign-reversing s-wave superconductors: analysis of iron oxypnictide superconductors Yuko Senga and Hiroshi Kontani Intrinsic magnetic properties of the superconductor NdFeAsO0.9F0.1 from local and global measurements R Prozorov, M E Tillman, E D Mun and P C Canfield

Elimination of impurity phase formation in FePt magnetic thin films prepared by pulsed laser deposition

International Nuclear Information System (INIS)

Wang, Ying; Medwal, Rohit; Sehdev, Neeru; Yadian, Boluo; Tan, T.L.; Lee, P.; Talebitaher, A.; Ilyas, Usman; Ramanujan, R.V.; Huang, Yizhong; Rawat, R.S.

2014-01-01

The formation of impurity phases in FePt thin films severely degrades its magnetic properties. The X-ray diffraction patterns of FePt thin films, synthesized using pulsed laser deposition (PLD), showed peaks corresponding to impurity phases, resulting in softer magnetic properties. A systematic investigation was carried to determine the factors that might have led to impurity phase formation. The factors include (i) PLD target composition, (ii) substrate material, (iii) annealing parameters such as temperature, duration and ambience and (iv) PLD deposition parameters such as chamber ambience, laser energy fluence and target–substrate distance. Depositions on the different substrates revealed impurity phase formation only on Si substrates. It was found that the target composition, PLD chamber ambience, and annealing ambience were not the factors that caused the impurity phase formation. The annealing temperature and duration influenced the impurity phases, but are not the cause of their formation. A decrease in the laser energy fluence and increase of the target–substrate distance resulted in elimination of the impurity phases and enhancement in the magnetic and structural properties of FePt thin films. The energy of the ablated plasma species, controlled by the laser energy fluence and the target–substrate distance, is found to be the main factor responsible for the formation of the impurity phases.

Design and demonstration of adiabatic quantum-flux-parametron logic circuits with superconductor magnetic shields

International Nuclear Information System (INIS)

Inoue, Kenta; Narama, Tatsuya; Yamanashi, Yuki; Yoshikawa, Nobuyuki; Takeuchi, Naoki

2015-01-01

Adiabatic quantum-flux-parametron (AQFP) logic is an energy-efficient superconductor logic with zero static power and very small dynamic power due to adiabatic switching operations. In order to build large-scale digital circuits, we built AQFP logic cells using superconductor magnetic shields, which are necessary in order to avoid unwanted magnetic couplings between the cells and excitation currents. In preliminary experimental tests, we confirmed that the unwanted coupling became negligibly small thanks to the superconductor shields. As a demonstration, we designed a four-to-one multiplexor and a 16-junction full adder using the shielded logic cells. In both circuits, we confirmed correct logic operations with wide operation margins of excitation currents. These results indicate that large-scale AQFP digital circuits can be realized using the shielded logic cells. (paper)

X-ray photoelectron spectroscopy of high-temperature superconductor clean surfaces and interfaces

International Nuclear Information System (INIS)

Hill, D.M.

1989-01-01

X-ray photoelectron spectroscopy was used to determine the characteristic spectra for the high temperature superconductors La 1.85 Sr 0.15 CuO 4 , YBa 2 Cu 3 O 7-x , and Bi 2 Sr 2-x Ca 1+x Cu 2 O 8+y and their impurity phases. The oxidation state of Cu in all of these materials was predominantly Cu 2+ . The O 1s emission for clean surfaces was a single broad peak near 529 eV derived from emission from inequivalent O sites in the superconductors. The valence bands were a -6 eV wide manifold of Cu 3d-O 2p hybrid bands in the ∼ 1-7 eV binding energy range, with very low emission at E F arising from antibonding Cu 3d-O 2p orbitals. Emission from grain boundary and other impurity phases appeared at 531 eV for the O 1s core level, and in general ∼ 1-2 eV higher energy than the superconductor peak for other core levels except for Cu 2p. Impurity phases appeared in the valence bands as a shoulder at ∼ 5 eV. The amount of impurities detected was shown to be dependent on the fracture properties of the superconductors. All of the materials were shown to be stable under vacuum. The products and spatial extent of chemical reactions with Ag, Al, Al oxide, Au, Bi, Bi oxide, CaF 2 , Cu, Fe, Si, and Si oxide overlayers on these materials also were examined. Au, CaF 2 , and metal oxides deposited by activated oxidation during evaporation were non-reactive and non-disruptive of the superconductor surfaces. Ag overlayers were unique in that they disrupted the superconductor during deposition, but exhibited no evidence of any chemical reactions. Overlayers with an affinity for oxygen withdrew O from the superconductor. The O loss occurred preferentially from Cu atoms in the superconductor and disrupted the planar bonding structure

Magnetic Fluctuations in Pair-Density-Wave Superconductors

Science.gov (United States)

Christensen, Morten H.; Jacobsen, Henrik; Maier, Thomas A.; Andersen, Brian M.

2016-04-01

Pair-density-wave superconductivity constitutes a novel electronic condensate proposed to be realized in certain unconventional superconductors. Establishing its potential existence is important for our fundamental understanding of superconductivity in correlated materials. Here we compute the dynamical magnetic susceptibility in the presence of a pair-density-wave ordered state and study its fingerprints on the spin-wave spectrum including the neutron resonance. In contrast to the standard case of d -wave superconductivity, we show that the pair-density-wave phase exhibits neither a spin gap nor a magnetic resonance peak, in agreement with a recent neutron scattering experiment on underdoped La1.905 Ba0.095 CuO4 [Z. Xu et al., Phys. Rev. Lett. 113, 177002 (2014)].

Surface flux density distribution characteristics of bulk high-T{sub c} superconductor in external magnetic field

Energy Technology Data Exchange (ETDEWEB)

Torii, S.; Yuasa, K

2004-10-01

Various magnetic levitation systems using oxide superconductors are developed as strong pinning forces are obtained in melt-processed bulk. However, the trapped flux of superconductor is moved by flux creep and fluctuating magnetic field. Therefore, to examine the internal condition of superconductor, the authors measure the dynamic surface flux density distribution of YBCO bulk. Flux density measurement system has a structure with the air-core coil and the Hall sensors. Ten Hall sensors are arranged in series. The YBCO bulk, which has 25 mm diameter and 13 mm thickness, is field cooled by liquid nitrogen. After that, magnetic field is changed by the air-core coil. This paper describes about the measured results of flux density distribution of YBCO bulk in the various frequencies of air-core coils currents.

Magnetic levitation and its application for education devices based on YBCO bulk superconductors

International Nuclear Information System (INIS)

Yang, W.M.; Chao, X.X.; Guo, F.X.; Li, J.W.; Chen, S.L.

2013-01-01

Highlights: • A small superconducting maglev propeller system has been designed and constructed based on YBCO bulk superconductors. • Several small maglev vehicle models have been designed and constructed based on YBCO bulk superconductors. • The models can be used as experimental or demonstration devices for the magnetic levitation applications. -- Abstract: A small superconducting maglev propeller system, a small spacecraft model suspending and moving around a terrestrial globe, several small maglev vehicle models and a magnetic circuit converter have been designed and constructed. The track was paved by NdFeB magnets, the arrangement of the magnets made us easy to get a uniform distribution of magnetic field along the length direction of the track and a high magnetic field gradient in the lateral direction. When the YBCO bulks mounted inside the vehicle models or spacecraft model was field cooled to LN 2 temperature at a certain distance away from the track, they could be automatically floating over and moving along the track without any obvious friction. The models can be used as experimental or demonstration devices for the magnetic levitation applications

Magnetic levitation and its application for education devices based on YBCO bulk superconductors

Energy Technology Data Exchange (ETDEWEB)

Yang, W.M., E-mail: yangwm@snnu.edu.cn; Chao, X.X.; Guo, F.X.; Li, J.W.; Chen, S.L.

2013-10-15

Highlights: • A small superconducting maglev propeller system has been designed and constructed based on YBCO bulk superconductors. • Several small maglev vehicle models have been designed and constructed based on YBCO bulk superconductors. • The models can be used as experimental or demonstration devices for the magnetic levitation applications. -- Abstract: A small superconducting maglev propeller system, a small spacecraft model suspending and moving around a terrestrial globe, several small maglev vehicle models and a magnetic circuit converter have been designed and constructed. The track was paved by NdFeB magnets, the arrangement of the magnets made us easy to get a uniform distribution of magnetic field along the length direction of the track and a high magnetic field gradient in the lateral direction. When the YBCO bulks mounted inside the vehicle models or spacecraft model was field cooled to LN{sub 2} temperature at a certain distance away from the track, they could be automatically floating over and moving along the track without any obvious friction. The models can be used as experimental or demonstration devices for the magnetic levitation applications.

Time dependence of magnetization of high temperature superconductors

International Nuclear Information System (INIS)

Larkin, A.I.; Geshkenbein, V.B.

1988-10-01

Magnetization of high T c superconductors logarithmically decreases with time. There is a maximum in the temperature dependence of the coefficient at this logarithm. If one assumes that there do exist two kinds of pinning centers, then this dependence can be described in the Anderson theory of thermal creeps of Abrikosov's vortices. The temperature dependence of the critical current is also discussed. (author). 23 refs

Moessbauer study of LaFeAsO and F-doped superconductors in external magnetic fields

International Nuclear Information System (INIS)

Kitao, S; Kobayashi, Y; Higashitaniguchi, S; Kurokuzu, M; Saito, M; Seto, M; Mitsui, T; Kamihara, Y; Hirano, M; Hosono, H

2010-01-01

The iron-based F-doped superconductors LaFeAsO 1-x F x with a transition temperature of 24 K (for x = 0.07) and 26 K (x = 0.11) and its parent material LaFeAsO were studied using 57 Fe Moessbauer spectroscopy. Further investigation was carried out by applying external magnetic fields. F-doped superconductors showed a singlet pattern with no magnetic splitting throughout the temperature range from 4.2 to 298 K. On the other hand, magnetically-split spectra were observed in the parent LaFeAsO below the Neel temperature of about 140 K. The internal magnetic field reached 5.3 T at 4.2 K. The external magnetic fields up to 14 T were applied to the singlet phases, F-doped superconductors and the parent LaFeAsO above the Neel temperature. The induced magnetically-split spectra showed the internal magnetic fields with the comparable value to the applied fields. This fact confirmed that these singlet phases have the paramagnetic feature. The magnetic fields were also applied to the magnetically-ordered phase of LaFeAsO below the Neel temperature. The evolution of the spectra depending on the external magnetic fields was clearly explained by a model with two sublattice spins of the powdered antiferromagnet. This fact confirmed the magnetically-ordered phase is an antiferromagnet. The spin-flop field was also estimated by the model as about 26 T.

Signatures of Majorana bound states in one-dimensional topological superconductors

International Nuclear Information System (INIS)

Pientka, Falko

2014-01-01

experimental manifestation of Majoranas is a zero-bias peak in the differential conductance. Here we show that in multi-subband wires the Majorana conductance peak can be suppressed compared to a strictly one-dimensional system, thereby providing a plausible explanation for recent experimental results. Based on this analysis, we furthermore predict an enhancement of the signature by deliberately introducing disorder, which could establish strong evidence for a Majorana bound state. A very recent proposal to realize a topological superconductor is based on a chain of magnetic impurities on the surface of a conventional superconductor. Here we derive a microscopic model in terms of the Shiba states bound to the individual impurities in the superconductor. Under realistic experimental conditions, the model involves long-range couplings leading to a new kind of topological phase transition and remarkable localization properties of the Majoranas. Finally, we investigate the tunneling spectroscopy of subgap states in superconductors. We develop a theory to describe the differential tunneling conductance from a superconducting tip into a localized quasiparticle state including relaxation processes present at nonzero temperature. Our result are in good agreement with experimental data on Shiba states and give access to properties of the bound state such as the local density of states and the nature of the relevant relaxation processes.

Superconductors

International Nuclear Information System (INIS)

1988-01-01

The chapter 6.3 p. 143 to 153 of this book deals with superconductors 19 items are briefly presented with address of manufacturer or laboratory to contact, mainly in the USA or Japan. In particular magnets, films, high temperature superconductors and various applications are presented [fr

Influence of an ergodic magnetic limiter on the impurity content in a tokamak

International Nuclear Information System (INIS)

Engelhardt, W.; Feneberg, W.

1978-01-01

This work deals with the properties of an ergodic magnetic limiter and presents calculations concerning the reduction of the impurity rate in a tokamak by a boundary sheath with decreased confinement time. The layer is produced by resonant helical windings superposed on an equilibrium magnetic field with closed magnetic surfaces. The transport coefficients in the boundary layer, which yield the temperature and density distribution, are obtained from the movement of particles along a stochastic magnetic field. The resulting line density can be made a factor of ten higher than is expected for a poloidal divertor experiment. From this it is concluded that all impurities coming from the wall will be ionized in the boundary layer. The concentration of the impurities in the plasma center is calculated according to a model which uses an anomalous diffusion coefficient being consistent with the ergodization in the boundary layer. The resulting concentration can be reduced proportional to the factor (nsub(e)Dsub(e)) -1 where nsub(e) and Dsub(e) are electron density and diffusion coefficient in the boundary layer. (Auth.)

Maximum repulsed magnetization of a bulk superconductor with low pulsed field

International Nuclear Information System (INIS)

Tsuchimoto, M.; Kamijo, H.; Fujimoto, H.

2005-01-01

Pulsed field magnetization of a bulk high-T c superconductor (HTS) is important technique especially for practical applications of a bulk superconducting magnet. Full magnetization is not obtained for low pulsed field and trapped field is decreased by reversed current in the HTS. The trapped field distribution by repulsed magnetization was previously reported in experiments with temperature control. In this study, repulsed magnetization technique with the low pulsed field is numerically analyzed under assumption of variable shielding current by the temperature control. The shielding current densities are discussed to obtain maximum trapped field by two times of low pulsed field magnetizations

Magnetic field dependence of ultrasound velocity in high-Tc superconductors

International Nuclear Information System (INIS)

Higgins, M.J.; Goshorn, D.P.; Bhattacharya, S.; Johnston, D.C.

1989-01-01

The magnetic field dependence of ultrasound velocity in the superconductor La 1.8 Sr 0.2 CuO 4-y is studied. The sound velocity anomaly near T c is shown to be unambiguously related to superconductivity. Below T c , the sound velocity is found to be sensitive to the dynamics of a pinned flux lattice. A combination of sound velocity and magnetization measurements suggests three regimes of pinning behavior. A generic pinning ''phase diagram'' is obtained in the superconducting state. An anomalous peak effect in the magnetization is also observed at intermediate field strengths

Theoretical approach to direct resonant inelastic X-ray scattering on magnets and superconductors

Energy Technology Data Exchange (ETDEWEB)

Marra, Pasquale

2015-10-26

The capability to probe the dispersion of elementary spin, charge, orbital, and lattice excitations has positioned resonant inelastic X-ray scattering (RIXS) at the forefront of photon science. In this work, we will investigate how RIXS can contribute to a deeper understanding of the orbital properties and of the pairing mechanism in unconventional high-temperature superconductors. In particular, we show how direct RIXS spectra of magnetic excitations can reveal long-range orbital correlations in transition metal compounds, by discriminating different kind of orbital order in magnetic and antiferromagnetic systems. Moreover, we show how RIXS spectra of quasiparticle excitations in superconductors can measure the superconducting gap magnitude, and reveal the presence of nodal points and phase differences of the superconducting order parameter on the Fermi surface. This can reveal the properties of the underlying pairing mechanism in unconventional superconductors, in particular cuprates and iron pnictides, discriminating between different superconducting order parameter symmetries, such as s,d (singlet pairing) and p wave (triplet pairing).

The effect of magnetic field and donor impurity on electron spectrum in spherical core-shell quantum dot

Science.gov (United States)

Holovatsky, V. A.; Voitsekhivska, O. M.; Yakhnevych, M. Ya

2018-04-01

The effect of homogeneous magnetic field and location of donor impurity on the electron energy spectrum and distribution of its probability density in spherical core-shell quantum dot is investigated. In the framework of the effective mass approximation and rectangular infinitely deep potential well, the solutions of the Schrodinger equation are found using the matrix method. The wave functions are expanded over the complete set of exact functions obtained without the magnetic field and impurity. It is shown that when the induction of magnetic field increases, the ground state of electron in the nanostructure without impurity or on-center impurity is successively formed by the states with m = 0, -1, -2, … (Aharonov-Bohm effect). When donor impurity is located in the shell of the nanostructure the Aharonov-Bohm effect vanishes. The dependences of electron energy spectrum and its wave functions on the location of impurity, placed along the direction of magnetic field or perpendicularly to it, are studied. It is shown, that in the first case, the quantum states are characterized by the certain value of magnetic quantum number m and the expansion contains the wave functions of the states with it only. In the second case, the cylindrical symmetry of the problem is broken and the new quantum states are formed from the states with different values of all three quantum numbers n, l, m and electron energy spectrum weakly depends on the magnetic field induction.

Granular Superconductors and Gravity

Science.gov (United States)

Noever, David; Koczor, Ron

1999-01-01

As a Bose condensate, superconductors provide novel conditions for revisiting previously proposed couplings between electromagnetism and gravity. Strong variations in Cooper pair density, large conductivity and low magnetic permeability define superconductive and degenerate condensates without the traditional density limits imposed by the Fermi energy (approx. 10(exp -6) g cu cm). Recent experiments have reported anomalous weight loss for a test mass suspended above a rotating Type II, YBCO superconductor, with a relatively high percentage change (0.05-2.1%) independent of the test mass' chemical composition and diamagnetic properties. A variation of 5 parts per 104 was reported above a stationary (non-rotating) superconductor. In experiments using a sensitive gravimeter, bulk YBCO superconductors were stably levitated in a DC magnetic field and exposed without levitation to low-field strength AC magnetic fields. Changes in observed gravity signals were measured to be less than 2 parts in 108 of the normal gravitational acceleration. Given the high sensitivity of the test, future work will examine variants on the basic magnetic behavior of granular superconductors, with particular focus on quantifying their proposed importance to gravity.

Kramers non-magnetic superconductivity in LnNiAsO superconductors.

Science.gov (United States)

Li, Yuke; Luo, Yongkang; Li, Lin; Chen, Bin; Xu, Xiaofeng; Dai, Jianhui; Yang, Xiaojun; Zhang, Li; Cao, Guanghan; Xu, Zhu-an

2014-10-22

We investigated a series of nickel-based oxyarsenides LnNiAsO (Ln=La, Ce, Pr, Nd, Sm) compounds. CeNiAsO undergoes two successive anti-ferromagnetic transitions at TN1=9.3 K and TN2=7.3 K; SmNiAsO becomes an anti-ferromagnet below TN≃3.5 K; NdNiAsO keeps paramagnetic down to 2 K but orders anti-ferromagnetically below TN≃1.3 K. Superconductivity was observed only in Kramers non-magnetic LaNiAsO and PrNiAsO with Tc=2.7 K and 0.93 K, respectively. The superconductivity of PrNiAsO is further studied by upper critical field and specific heat measurements, which reveal that PrNiAsO is a weakly coupled Kramers non-magnetic superconductor. Our work confirms that the nickel-based oxyarsenide superconductors are substantially different in mechanism to iron-based ones, and are likely to be described by the conventional superconductivity theory.

Magnetic impurities in single-wall carbon nanotubes and graphene: a review

Czech Academy of Sciences Publication Activity Database

Vejpravová, Jana; Pacáková, Barbara; Kalbáč, Martin

2016-01-01

Roč. 141, č. 9 (2016), s. 2639-2656 ISSN 0003-2654 R&D Projects: GA MŠk LL1301 Institutional support: RVO:68378271 ; RVO:61388955 Keywords : graphene * carbon nanotube * magnetic impurities Subject RIV: BM - Solid Matter Physics ; Magnetism; CF - Physical ; Theoretical Chemistry (UFCH-W) Impact factor: 3.885, year: 2016

Time-reversal breaking and spin transport induced by magnetic impurities in a 2D topological insulator

International Nuclear Information System (INIS)

Derakhshan, V; Ketabi, S A; Moghaddam, A G

2016-01-01

We employed the formalism of bond currents, expressed in terms of non-equilibrium Green’s function to obtain the local currents and transport features of zigzag silicene ribbon in the presence of magnetic impurity. When only intrinsic and Rashba spin–orbit interactions are present, silicene behaves as a two-dimensional topological insulator with gapless edge states. But in the presence of finite intrinsic spin–orbit interaction, the edge states start to penetrate into the bulk of the sample by increasing Rashba interaction strength. The exchange interaction induced by local impurities breaks the time-reversal symmetry of the gapless edge states and influences the topological properties strongly. Subsequently, the singularity of partial Berry curvature disappears and the silicene nanoribbon becomes a trivial insulator. On the other hand, when the concentration of the magnetic impurities is low, the edge currents are not affected significantly. In this case, when the exchange field lies in the x – y plane, the spin mixing around magnetic impurity is more profound rather than the case in which the exchange field is directed along the z -axis. Nevertheless, when the exchange field of magnetic impurities is placed in the x – y plane, a spin-polarized conductance is observed. The resulting conductance polarization can be tuned by the concentration of the impurities and even completely polarized spin transport is achievable. (paper)

Comparative study of magnetization in conventional and high Tc superconductors

International Nuclear Information System (INIS)

Sarkissian, B.V.B.; Grover, A.K.; Balakrishnan, G.; Paulose, P.L.; Vijayaraghavan, R.

1989-01-01

Results of a comparative study of thermomagnetic history effects and anomalous variations in isothermal magnetization hysteresis curves in a High T compound (YBa 2 Cu 3 O 7 ) with two specimens of Nb are presented. They show that the former behaves like any hard type c II superconductor

Conductance of graphene based normal-superconductor junction with double magnetic barriers

Science.gov (United States)

Abdollahipour, B.; Mohebalipour, A.; Maleki, M. A.

2018-05-01

We study conductance of a graphene based normal metal-superconductor junction with two magnetic barriers. The magnetic barriers are induced via two applied magnetic fields with the same magnitudes and opposite directions accompanied by an applied electrostatic potential. We solve Dirac-Bogoliubov-De-Gennes (DBdG) equation to calculate conductance of the junction. We find that applying the magnetic field leads to suppression of the Andreev reflection and conductance for all energies. On the other hand, we observe a crossover from oscillatory to tunneling behavior of the conductance as a function of the applied potential by increasing the magnetic field.

Irreversible magnetization deep in the vortex-liquid state of a 2D superconductor at high magnetic fields

International Nuclear Information System (INIS)

Maniv, T; Zhuravlev, V; Wosnitza, J; Hagel, J

2004-01-01

The remarkable phenomenon of weak magnetization hysteresis loops, observed recently deep in the vortex-liquid state of a nearly two-dimensional (2D) superconductor at low temperatures and high magnetic fields, is shown to reflect the existence of an unusual vortex-liquid state, consisting of collectively pinned crystallites of easily sliding vortex chains. (letter to the editor)

Superconductor-ferromagnet-superconductor nanojunctions from perovskite materials

International Nuclear Information System (INIS)

Štrbík, V.; Beňačka, Š.; Gaži, Š.; Španková, M.; Šmatko, V.; Knoška, J.; Gál, N.; Chromik, Š.; Sojková, M.; Pisarčík, M.

2017-01-01

Highlights: • Superconductor-ferromagnet-superconductor nanojunction. • Nanojunctions prepared by Ga"3"+ focused ion beam patterning. • Indication of triplet Cooper pair component in junction superconducting current. • Qualitative agreement with theoretical model. - Abstract: The lateral superconductor-ferromagnet–superconductor (SFS) nanojunctions based on high critical temperature superconductor YBa_2Cu_3O_x (YBCO) and half-metallic ferromagnet La_0_._6_7Sr_0_._3_3MnO_3 (LSMO) thin films were prepared to investigate a possible presence of long range triplet component (LRTC) of Cooper pairs in the LSMO. We applied Ga"3"+ focused ion beam patterning to create YBCO/LSMO/YBCO lateral type nanojunctions with LSMO length as small as 40 nm. The resistivity vs. temperature, critical current density vs. temperature and resistance vs. magnetic field dependence were studied to recognize the LRTC of Cooper pairs in the LSMO. A non-monotonic temperature dependence of junction critical current density and a decrease of the SFS nanojunction resistance in increased magnetic field were observed. Only weak manifestations of LRTC and some qualitative agreement with theory were found out in SFS nanojunctions realized from the perovskite materials. The presence of equal-spin triplet component of Cooper pairs in half-metallic LSMO ferromagnet is not such apparent as in SFS junctions prepared from low temperature superconductors NbTiN and half-metallic ferromagnet CrO_2.

Notes on analytical study of holographic superconductors with Lifshitz scaling in external magnetic field

International Nuclear Information System (INIS)

Zhao, Zixu; Pan, Qiyuan; Jing, Jiliang

2014-01-01

We employ the matching method to analytically investigate the holographic superconductors with Lifshitz scaling in an external magnetic field. We discuss systematically the restricted conditions for the matching method and find that this analytic method is not always powerful to explore the effect of external magnetic field on the holographic superconductors unless the matching point is chosen in an appropriate range and the dynamical exponent z satisfies the relation z=d−1 or z=d−2. From the analytic treatment, we observe that Lifshitz scaling can hinder the condensation to be formed, which can be used to back up the numerical results. Moreover, we study the effect of Lifshitz scaling on the upper critical magnetic field and reproduce the well-known relation obtained from Ginzburg–Landau theory

Melt processed high-temperature superconductors

CERN Document Server

1993-01-01

The achievement of large critical currents is critical to the applications of high-temperature superconductors. Recent developments have shown that melt processing is suitable for producing high J c oxide superconductors. Using magnetic forces between such high J c oxide superconductors and magnets, a person could be levitated.This book has grown largely out of research works on melt processing of high-temperature superconductors conducted at ISTEC Superconductivity Research Laboratory. The chapters build on melt processing, microstructural characterization, fundamentals of flux pinning, criti

Magnetic torque transferring study for bulk High-Tc superconductors and permanent magnets

International Nuclear Information System (INIS)

Wongsatanawarid, A; Suzuki, A; Seki, H; Murakami, M

2009-01-01

The torque transferring mechanism taking place in a superconducting mixer design has been studied. Several coupling magnetic arrangements were investigated for more details in the engineering design. A bulk superconductor sample was used to study the torque forces for various cooling gaps, and the twist angle dependence was also monitored for the rotational stiffness in stability. The experimental data with four permanent magnet configurations have been studied in the present work. The maximum torque forces are summarized for usage of engineering design with various gaps. The torque/gap characteristics for four configurations were also measured for the optimisation of the torque at a designed operating gap.

Tunable Majorana corner states in a two-dimensional second-order topological superconductor induced by magnetic fields

Science.gov (United States)

Zhu, Xiaoyu

2018-05-01

A two-dimensional second-order topological superconductor exhibits a finite gap in both bulk and edges, with the nontrivial topology manifesting itself through Majorana zero modes localized at the corners, i.e., Majorana corner states. We investigate a time-reversal-invariant topological superconductor in two dimensions and demonstrate that an in-plane magnetic field could transform it into a second-order topological superconductor. A detailed analysis reveals that the magnetic field gives rise to mass terms which take distinct values among the edges, and Majorana corner states naturally emerge at the intersection of two adjacent edges with opposite masses. With the rotation of the magnetic field, Majorana corner states localized around the boundary may hop from one corner to a neighboring one and eventually make a full circle around the system when the field rotates by 2 π . In the end, we briefly discuss physical realizations of this system.

Electronic structure and magnetic properties of dilute U impurities in metals

Science.gov (United States)

Mohanta, S. K.; Cottenier, S.; Mishra, S. N.

2016-05-01

The electronic structure and magnetic moment of dilute U impurity in metallic hosts have been calculated from first principles. The calculations have been performed within local density approximation of the density functional theory using Augmented plane wave+local orbital (APW+lo) technique, taking account of spin-orbit coupling and Coulomb correlation through LDA+U approach. We present here our results for the local density of states, magnetic moment and hyperfine field calculated for an isolated U impurity embedded in hosts with sp-, d- and f-type conduction electrons. The results of our systematic study provide a comprehensive insight on the pressure dependence of 5f local magnetism in metallic systems. The unpolarized local density of states (LDOS), analyzed within the frame work of Stoner model suggest the occurrence of local moment for U in sp-elements, noble metals and f-block hosts like La, Ce, Lu and Th. In contrast, U is predicted to be nonmagnetic in most transition metal hosts except in Sc, Ti, Y, Zr, and Hf consistent with the results obtained from spin polarized calculation. The spin and orbital magnetic moments of U computed within the frame of LDA+U formalism show a scaling behavior with lattice compression. We have also computed the spin and orbital hyperfine fields and a detail analysis has been carried out. The host dependent trends for the magnetic moment, hyperfine field and 5f occupation reflect pressure induced change of electronic structure with U valency changing from 3+ to 4+ under lattice compression. In addition, we have made a detailed analysis of the impurity induced host spin polarization suggesting qualitatively different roles of f-band electrons on moment stability. The results presented in this work would be helpful towards understanding magnetism and spin fluctuation in U based alloys.

Spin polarization of electrons in a magnetic impurity doped ...

Indian Academy of Sciences (India)

Abstract. A theoretical model is presented in this paper for degree of spin polarization in a light emitting diode (LED) whose epitaxial region contains quantum dots doped with magnetic impurity. The model is then used to investigate the effect of electron–phonon interaction on degree of spin polarization at different ...

Spin polarization of electrons in a magnetic impurity doped ...

Indian Academy of Sciences (India)

A theoretical model is presented in this paper for degree of spin polarization in alight emitting diode (LED) whose epitaxial region contains quantum dots doped with magnetic impurity. The model is then used to investigate the effect of electron–phonon interaction on degree of spin polarization at different temperatures and ...

Effects of magnetic impurity scattering on superfluid 3He in aerogel

Science.gov (United States)

Aoyama, Kazushi; Ikeda, Ryusuke

2009-02-01

We investigate impurity effects on superfluid 3He in aerogel whose surface is not coated with 4He, different from most experimental situations. In systems with no 4He coating, spins of solid 3He absorbed on the aerogel surface are active and interact with spins of quasiparticles relevant to superfluidity and, for this reason, such an aerogel is treated as magnetic scatterers. It is found that, in the ABM pairing state affected by magnetic scatterings, not only the l-vector but also the d-vector has no long-ranged orientational order, and that the strong-coupling correction due to impurity scatterings is less suppressed than that in the nonmagnetic case, implying an expansion of the A-like phase region.

Development of Y-Ba-Cu-O Superconductors for Magnetic Bearings

Science.gov (United States)

Selvamanickam, V.; Pfaffenbach, K.; Sokolowski, R. S.; Zhang, Y.; Salama, K.

1996-01-01

The material requirements, material manufacturing and magnetic properties that are relevant to fabrication of High Temperature Superconductor (HTS) magnetic bearings have been discussed. It is found that the seeded-melt-texturing method can be used to fabricate the single domain material that is required to achieve the best magnetic properties. Trapped-field mapping has been used as a non-destructive tool to determine the single-domain nature of the HTS material and quantity of the HTS disks. Both the trapped field and the levitation force of the Y-Ba-Cu-O disks are found to be strongly sensitive to the oxygen content.

Voltage from mechanical stress in type-II superconductors: Depinning of the magnetic flux by moving dislocations

OpenAIRE

Albert, Jaroslav; Chudnovsky, Eugene M.

2008-01-01

Mechanical stress causes motion of defects in solids. We show that in a type-II superconductor a moving dislocation generates a pattern of current that exerts the depinning force on the surrounding vortex lattice. Concentration of dislocations and the mechanical stress needed to produce critical depinning currents are shown to be within practical range. When external magnetic field and transport current are present this effect generates voltage across the superconductor. Thus a superconductor...

Normal state magnetic behavior of (U/sub 1-x/RE/sub x/)Be13 pseudobinaries

International Nuclear Information System (INIS)

Zirngiebl, E.; Thompson, J.D.; Smith, J.L.; Fisk, Z.

1987-01-01

Any impurity doping seems to modify the low temperature properties of UBe 13 in a way rather unusual compared to normal superconductors. So far, however, little attention has been paid to the modification of the normal state properties of impurity doped UB 13 . We have investigated the normal state magnetic behavior of impurity doped (U/sub 1-x/RE/sub x/)Be 13 pseudobinaries (RE = Th, Y, La, Lu, Sc) in the temperature range between 2 K and 380 K for impurity concentrations x ≤ 0.05 to see if there are correlations with T/sub c/(x)

Pinning and creep in superconductors

International Nuclear Information System (INIS)

Ovchinnikov, Yu.N.

1994-01-01

All superconductors can be separated into two large groups: type I and type II. The behaviour of these two groups in a magnetic field is quite different. The superconductors of type I, in a strong magnetic field, enter the intermediate state. Phenomenological picture of this state was given by Landau. The type II superconductors, in strong magnetic fields, form the mixed state (or Shubnikov phase). The microscopic picture of the mixed state was given by Abrikosov on the basis of Ginzburg-Landau equations. In ideal homogeneous superconductors the free energy is not changed if all the vortex structure is shifted on some distance u. The transport current will be proportional, therefore, to the electric field E. All the real superconductors, however, are inhomogeneous. Inhomogeneities interact with vortex lattice and pin it. In this new state the transport current below some critical value does not lead to the motion of the flux lattice and to the energy dissipation. The value of critical current strongly depends on the type of inhomogeneities, on the value of magnetic field and on temperature. In new layered superconductors, the critical current depends also on the orientation of the magnetic field B with respect to the layer planes. Temperature and quantum fluctuations lead to the transition between different metastable states in superconductors with current. As a result, the vortex lattice slowly moves (creep phenomenon). Below we will briefly discuss all these phenomena. (orig.)

Effective equations for the precession dynamics of electron spins and electron–impurity correlations in diluted magnetic semiconductors

International Nuclear Information System (INIS)

Cygorek, M; Axt, V M

2015-01-01

Starting from a quantum kinetic theory for the spin dynamics in diluted magnetic semiconductors, we derive simplified equations that effectively describe the spin transfer between carriers and magnetic impurities for an arbitrary initial impurity magnetization. Taking the Markov limit of these effective equations, we obtain good quantitative agreement with the full quantum kinetic theory for the spin dynamics in bulk systems at high magnetic doping. In contrast, the standard rate description where the carrier–dopant interaction is treated according to Fermi’s golden rule, which involves the assumption of a short memory as well as a perturbative argument, has been shown previously to fail if the impurity magnetization is non-zero. The Markov limit of the effective equations is derived, assuming only a short memory, while higher order terms are still accounted for. These higher order terms represent the precession of the carrier–dopant correlations in the effective magnetic field due to the impurity spins. Numerical calculations show that the Markov limit of our effective equations reproduces the results of the full quantum kinetic theory very well. Furthermore, this limit allows for analytical solutions and for a physically transparent interpretation. (paper)

Turbulent transport of impurities in a magnetized plasma; Transport turbulent d'impuretes dans un plasma magnetise

Energy Technology Data Exchange (ETDEWEB)

Dubuit, N

2006-10-15

This work deals with the transport of impurities in magnetically confined thermonuclear plasmas. The accumulation of impurities in the core of the plasma would imply dramatic losses of energy that may lead to the extinction of the plasma. On the opposite, the injection of impurities in the plasma edge is considered as an efficient means to extract heat without damaging the first wall. The balance between these 2 contradictory constraints requires an accurate knowledge of the impurity transport inside the plasma. The effect of turbulence, the main transport mechanism for impurities is therefore a major issue. In this work, the complete formula of a turbulent flow of impurities for a given fluctuation spectrum has been inferred. The origin and features of the main accumulation processes have been identified. The main effect comes from the compressibility of the electrical shift speed in a plane perpendicular to the magnetic field. This compressibility appears to be linked to the curvature of the magnetic field. A less important effect is a thermal-diffusion process that is inversely proportional to the number of charges and then disappears for most type of impurities except the lightest. This effect implies an impurity flux proportional to the temperature gradient and its direction can change according to the average speed of fluctuations. A new version of the turbulence code TRB has been developed. This new version allows the constraints of the turbulence not by the gradients but by the flux which is more realistic. The importance of the processes described above has been confirmed by a comparison between calculation and experimental data from Tore-supra and the Jet tokamak. The prevailing role of the curvature of the magnetic field in the transport impurity is highlighted. (A.C.)

Equivalent Coil Model for Computing Levitation Forces Between Permanent Magnets and High Temperatures Superconductors; Modelo de Espira Equivalente para el Calculo de Fuerzas de Levitacion Magnetica entre Imanes Permanentes y Superconductores de Alta Temperatura Critica

Energy Technology Data Exchange (ETDEWEB)

Cavia Santos, S; Garcia-Tabares, L

1998-05-01

A new simple theory has been developed for the study of levitation forces between a permanent magnet and a HTc superconductor. This theory is based on the assumption that both, the magnet and the superconductor, can be modelled by an equivalent coil placed on their surface. While the current flowing through the permanent magnet is constant, the equivalent current through the superconductor can be iether corresponding to screen the overall flux or a constant current corresponding to critical current density when the superconductor is saturated. A test facility has been designed and built for measuring levitation forces at variable approaching speeds. Comparison between theoretical and experimental measurements are presented in the report as well as a general description of the test facility. (Author)

Muon spin rotation studies of electronic excitations and magnetism in the vortex cores of superconductors

International Nuclear Information System (INIS)

Sonier, J E

2007-01-01

The focus of this paper is on recent progress in muon spin rotation (μSR) studies of the vortex cores in type-II superconductors. By comparison of μSR measurements of the vortex core size in a variety of materials with results from techniques that directly probe electronic states, the effect of delocalized quasiparticles on the spatial variation of field in a lattice of interacting vortices has been determined for both single-band and multi-band superconductors. These studies demonstrate the remarkable accuracy of what some still consider an exotic technique. In recent years μSR has also been used to search for magnetism in and around the vortex cores of high-temperature superconductors. As a local probe μSR is specially suited for detecting static or quasistatic magnetism having short-range or random spatial correlations. As discussed in this review, μSR experiments support a generic phase diagram of competing superconducting and magnetic order parameters, characterized by a quantum phase transition to a state where the competing order is spatially nonuniform

Superconductor-ferromagnet-superconductor nanojunctions from perovskite materials

Energy Technology Data Exchange (ETDEWEB)

Štrbík, V., E-mail: vladimir.strbik@savba.sk [Institute of Electrical Engineering, SAS, Dúbravská Cesta 9, Bratislava (Slovakia); Beňačka, Š.; Gaži, Š.; Španková, M.; Šmatko, V. [Institute of Electrical Engineering, SAS, Dúbravská Cesta 9, Bratislava (Slovakia); Knoška, J. [Center for Free-Electron Laser Science, DESY, Notkestraße 85, 22607, Hamburg (Germany); Department of Physics, University of Hamburg, Luruper Chaussee 149, 22607, Hamburg (Germany); Gál, N.; Chromik, Š.; Sojková, M.; Pisarčík, M. [Institute of Electrical Engineering, SAS, Dúbravská Cesta 9, Bratislava (Slovakia)

2017-02-15

Highlights: • Superconductor-ferromagnet-superconductor nanojunction. • Nanojunctions prepared by Ga{sup 3+} focused ion beam patterning. • Indication of triplet Cooper pair component in junction superconducting current. • Qualitative agreement with theoretical model. - Abstract: The lateral superconductor-ferromagnet–superconductor (SFS) nanojunctions based on high critical temperature superconductor YBa{sub 2}Cu{sub 3}O{sub x} (YBCO) and half-metallic ferromagnet La{sub 0.67}Sr{sub 0.33}MnO{sub 3} (LSMO) thin films were prepared to investigate a possible presence of long range triplet component (LRTC) of Cooper pairs in the LSMO. We applied Ga{sup 3+} focused ion beam patterning to create YBCO/LSMO/YBCO lateral type nanojunctions with LSMO length as small as 40 nm. The resistivity vs. temperature, critical current density vs. temperature and resistance vs. magnetic field dependence were studied to recognize the LRTC of Cooper pairs in the LSMO. A non-monotonic temperature dependence of junction critical current density and a decrease of the SFS nanojunction resistance in increased magnetic field were observed. Only weak manifestations of LRTC and some qualitative agreement with theory were found out in SFS nanojunctions realized from the perovskite materials. The presence of equal-spin triplet component of Cooper pairs in half-metallic LSMO ferromagnet is not such apparent as in SFS junctions prepared from low temperature superconductors NbTiN and half-metallic ferromagnet CrO{sub 2}.

Response of hard superconductors to crossed magnetic fields: elliptic critical-state model

Energy Technology Data Exchange (ETDEWEB)

Romero-Salazar, C.; Perez-Rodriguez, F

2004-05-01

The behavior of hard superconductors subjected to crossed magnetic fields is theoretically investigated by employing an elliptic critical-state model. Here the anisotropy is induced by flux-line cutting. The model reproduces successfully the collapse of the magnetic moment under the action of a sweeping magnetic field, applied perpendicularly to a dc field, for diamagnetic and paramagnetic initial states. Besides, it explains the transition from the diamagnetic state to the paramagnetic one when the magnitudes of the crossed magnetic fields are of the same order.

Binding energy of impurity states in an inverse parabolic quantum well under magnetic field

International Nuclear Information System (INIS)

Kasapoglu, E.; Sari, H.; Soekmen, I.

2007-01-01

We have investigated the effects of the magnetic field which is directed perpendicular to the well on the binding energy of the hydrogenic impurities in an inverse parabolic quantum well (IPQW) with different widths as well as different Al concentrations at the well center. The Al concentration at the barriers was always x max =0.3. The calculations were performed within the effective mass approximation, using a variational method. We observe that IPQW structure turns into parabolic quantum well with the inversion effect of the magnetic field and donor impurity binding energy in IPQW strongly depends on the magnetic field, Al concentration at the well center and well dimensions

First principles density functional calculation of magnetic moment and hyperfine fields of dilute transition metal impurities in Gd host

International Nuclear Information System (INIS)

Mohanta, S.K.; Mishra, S.N.; Srivastava, S.K.

2014-01-01

We present first principles calculations of electronic structure and magnetic properties of dilute transition metal (3d, 4d and 5d) impurities in a Gd host. The calculations have been performed within the density functional theory using the full potential linearized augmented plane wave technique and the GGA+U method. The spin and orbital contributions to the magnetic moment and the hyperfine fields have been computed. We find large magnetic moments for 3d (Ti–Co), 4d (Nb–Ru) and 5d (Ta–Os) impurities with magnitudes significantly different from the values estimated from earlier mean field calculation [J. Magn. Magn. Mater. 320 (2008) e446–e449]. The exchange interaction between the impurity and host Gd moments is found to be positive for early 3d elements (Sc–V) while in all other cases an anti-ferromagnetic coupling is observed. The trends for the magnetic moment and hyperfine field of d-impurities in Gd show qualitative difference with respect to their behavior in Fe, Co and Ni. The calculated total hyperfine field, in most cases, shows excellent agreement with the experimental results. A detailed analysis of the Fermi contact hyperfine field has been made, revealing striking differences for impurities having less or more than half filled d-shell. The impurity induced perturbations in host moments and the change in the global magnetization of the unit cell have also been computed. The variation within each of the d-series is found to correlate with the d–d hybridization strength between the impurity and host atoms. - Highlights: • Detailed study of transition metal impurities in ferromagnetic Gd has been carried out. • The trends in impurity magnetic moment are qualitatively different from Fe, Co and Ni. • The variation within each of the d-series is found to correlate with the d–d hybridization strength between the impurity and host atoms. • Experimental trend in a hyperfine field has been reproduced successfully

Development of superconductor bulk for superconductor bearing

Energy Technology Data Exchange (ETDEWEB)

Kim, Chan Joong; Jun, Byung Hyuk; Park, Soon Dong (and others)

2008-08-15

Current carrying capacity is one of the most important issues in the consideration of superconductor bulk materials for engineering applications. There are numerous applications of Y-Ba-Cu-O (YBCO) bulk superconductors e.g. magnetic levitation train, flywheel energy storage system, levitation transportation, lunar telescope, centrifugal device, magnetic shielding materials, bulk magnets etc. Accordingly, to obtain YBCO materials in the form of large, single crystals without weak-link problem is necessary. A top seeded melt growth (TSMG) process was used to fabricate single crystal YBCO bulk superconductors. The seeded and infiltration growth (IG) technique was also very promising method for the synthesis of large, single-grain YBCO bulk superconductors with good superconducting properties. 5 wt.% Ag doped Y211 green compacts were sintered at 900 .deg. C {approx} 1200 .deg.C and then a single crystal YBCO was fabricated by an infiltration method. A refinement and uniform distribution of the Y211 particles in the Y123 matrix were achieved by sintering the Ag-doped samples. This enhancement of the critical current density was ascribable to a fine dispersion of the Y211 particles, a low porosity and the presence of Ag particles. In addition, we have designed and manufactured large YBCO single domain with levitation force of 10-13 kg/cm{sup 2} using TSMG processing technique.

Three-dimensionality of field-induced magnetism in a high-temperature superconductor

DEFF Research Database (Denmark)

Lake, B.; Lefmann, K.; Christensen, N.B.

2005-01-01

Many physical properties of high-temperature superconductors are two-dimensional phenomena derived from their square-planar CuO(2) building blocks. This is especially true of the magnetism from the copper ions. As mobile charge carriers enter the CuO(2) layers, the antiferromagnetism of the parent...

Magnetic-Field-Enhanced Incommensurate Magnetic Order in the Underdoped High-Temperature Superconductor YBa2Cu3O6.45

DEFF Research Database (Denmark)

Haug, D.; Hinkov, V.; Suchaneck, A.

2009-01-01

We present a neutron-scattering study of the static and dynamic spin correlations in the underdoped high-temperature superconductor YBa2Cu3O6.45 in magnetic fields up to 15 T. The field strongly enhances static incommensurate magnetic order at low temperatures and induces a spectral-weight shift...

The disordered Bose condensate in two dimensions: application to high-Tc superconductors

International Nuclear Information System (INIS)

Gold, A.

1992-01-01

We calculate the dynamical conductivity for a weakly disordered Bose condensate in two dimensions. The disorder is due to neutral impurities. We compare the asymptotic laws (for small and large frequencies) for neutral impurities with the ones for charged impurities. Universal functions for the dynamical transport properties are derived. The plasmon density of states shows a linear increase with energy for intermediate energies and a peak structure at larger energies. Our theoretical results are compared with experimental results (far-infrared, electron-energy-loss and Raman spectroscopy) found in the high-Tc superconductor YBa 2 Cu 3 O 7-δ . The occurrence of a quasi-gap in a disordered Bose condensate is described and discussed in connection with experiments on high-Tc superconductors. (orig.)

Magnetization reversal of the transverse domain wall confined between two clusters of magnetic impurities in a ferromagnetic planar nanowire

Energy Technology Data Exchange (ETDEWEB)

Toscano, D., E-mail: danilotoscano@fisica.ufjf.br [Departamento de Física, Laboratório de Simulação Computacional, Universidade Federal de Juiz de Fora, Juiz de Fora, Minas Gerais 36036–330 (Brazil); Leonel, S.A., E-mail: sidiney@fisica.ufjf.br [Departamento de Física, Laboratório de Simulação Computacional, Universidade Federal de Juiz de Fora, Juiz de Fora, Minas Gerais 36036–330 (Brazil); Coura, P.Z., E-mail: pablo@fisica.ufjf.br [Departamento de Física, Laboratório de Simulação Computacional, Universidade Federal de Juiz de Fora, Juiz de Fora, Minas Gerais 36036–330 (Brazil); Sato, F., E-mail: sjfsato@fisica.ufjf.br [Departamento de Física, Laboratório de Simulação Computacional, Universidade Federal de Juiz de Fora, Juiz de Fora, Minas Gerais 36036–330 (Brazil); Costa, B.V., E-mail: bvc@fisica.ufmg.br [Departamento de Física, Laboratório de Simulação, Universidade Federal de Minas Gerais, Belo Horizonte, Minas Gerais 30123–970 (Brazil); Vázquez, M., E-mail: mvazquez@icmm.csic.es [Instituto de Ciencia de Materiales de Madrid, CSIC. 28049 Madrid (Spain)

2016-12-01

Numerical simulations have been used to investigate the polarity reversal of the transverse domain wall in rectangular magnetic nanowires and the stabilization of the domain wall position after occurring the polarity reversal. In order to control the wall position we have considered two clusters of magnetic impurities, identical and equidistant from the nanowire width axis. Traps of pinning and blocking for the transverse domain wall can be originated from magnetic impurities, consisting of a local variation of the exchange constant. Under suitable excitation amplitudes it is possible to switch the polarity of the transverse domain wall by applying a nanosecond axial magnetic field pulse in a fast and controllable way. - Highlights: • Traps for pinning and blocking transverse domain walls are proposed. • The traps consisting of localized modifications of the magnetic properties. • The wall polarity can be reversed in a fast and controllable way.

Effect of magnetic field on the impurity binding energy of the excited ...

Indian Academy of Sciences (India)

The effect of external magnetic field on the excited state energies in a spherical quantum dot was studied. The impurity energy and binding energy were calculated using the variational method within the effective mass approximation and finite barrier potential. The results showed that by increasing the magnetic field, the ...

Effect of magnetic field on the impurity binding energy of the excited ...

Indian Academy of Sciences (India)

Abstract. The effect of external magnetic field on the excited state energies in a spher- ical quantum dot was studied. The impurity energy and binding energy were calculated using the variational method within the effective mass approximation and finite barrier potential. The results showed that by increasing the magnetic ...

Property and microstructural nonuniformity in the yttrium-barium-copper-oxide superconductor determined from electrical, magnetic, and ultrasonic measurements

International Nuclear Information System (INIS)

Roth, D.J.

1991-01-01

This dissertation is presented in two major chapters. In the first chapter, the use of ultrasonic velocity for estimating pore fraction in YBCO and other polycrystalline materials is reviewed, modeled, and statistically analyzed. This chapter provides the basis for using ultrasonic velocity to interrogate microstructure. In the second chapter, (1) the effect of pore fraction (0.10-0.25) on superconductor properties of YBCO samples is characterized, (2) spatial (within-sample) variations in microstructure and superconductor properties are investigated and (3) the effect of oxygen content on elastic behavior is examined. Experimental methods used included a.c. susceptibility, electrical, and ultrasonic-velocity measurements. Superconductor properties measured included transition temperature, magnetic transition width, transport and magnetic critical current density, magnetic shielding, a.c. loss, and sharpness of the voltage-current characteristic. Superconductor properties including within-sample uniformity were generally poorest for samples containing the lowest (0.10) pore fraction. Ultrasonic velocity was linearly related to pore fraction thereby allowing sample classification. Changes in superconducting behavior were observed consistent with changes in oxygen content

Costs of magnets for large fusion power reactors: Phase I, cost of superconductors for dc magnets

International Nuclear Information System (INIS)

Powell, J.R.

1972-01-01

Projections are made for dc magnet conductor costs for large fusion power reactors. A mature fusion economy is assumed sometime after 2000 A. D. in which approximately 90,000 MW(e) of fusion reactors are constructed/year. State of the art critical current vs. field characteristics for superconductors are used in these projections. Present processing techniques are used as a basis for the design of large plants sized to produce approximately one-half of the conductor needed for the fusion magnets. Multifilamentary Nb-Ti, Pb-Bi in glass fiber, GE Nb 3 Sn tape, Linde plasma sprayed Nb 3 Sn tape, and V 3 Ga tape superconductors are investigated, together with high purity aluminum cryoconductor. Conductor costs include processing costs [capital (equipment plus buildings), labor, and operating] and materials costs. Conductor costs are compared for two sets of material costs: current (1971 A. D.) costs, and projected (after 2000 A. D.) costs. (U.S.)

Superconductor Dynamics

Energy Technology Data Exchange (ETDEWEB)

Gömöry, F [Bratislava, Inst. Elect. Eng. (Slovakia)

2014-07-01

Superconductors used in magnet technology could carry extreme currents because of their ability to keep the magnetic flux motionless. The dynamics of the magnetic flux interaction with superconductors is controlled by this property. The cases of electrical transport in a round wire and the magnetization of wires of various shapes (circular, elliptical, plate) in an external magnetic field are analysed. Resistance to the magnetic field penetration means that the field produced by the superconducting magnet is no longer proportional to the supplied current. It also leads to a dissipation of electromagnetic energy. In conductors with unequal transverse dimensions, such as flat cables, the orientation with respect to the magnetic field plays an essential role. A reduction of magnetization currents can be achieved by splitting the core of a superconducting wire into fine filaments; however, new kinds of electrical currents that couple the filaments consequently appear. Basic formulas allowing qualitative analyses of various flux dynamic cases are presented.

Magnetization reversal of a type-II superconductor thin disk under the action of a constant magnetic field

International Nuclear Information System (INIS)

Koval'chuk, D.G.; Chornomorets', M.P.

2010-01-01

The applicability of relations obtained by Clem and Sanchez for the ac magnetic susceptibility of type-II superconductor thin films to the case where an additional constant magnetic field is applied perpendicularly to the film has been analyzed in the framework of the critical state model. The issues concerning the sample 'memory' and the influence of the magnetic field change prehistory on the current sample state have been discussed. It has been shown that the ac component of the magnetic moment and, hence, the amplitudes of ac magnetic susceptibility harmonics are established within one period of the ac magnetic field irrespective of the field prehistory.

Modelling and comparison of trapped fields in (RE)BCO bulk superconductors for activation using pulsed field magnetization

Science.gov (United States)

Ainslie, M. D.; Fujishiro, H.; Ujiie, T.; Zou, J.; Dennis, A. R.; Shi, Y.-H.; Cardwell, D. A.

2014-06-01

The ability to generate a permanent, stable magnetic field unsupported by an electromotive force is fundamental to a variety of engineering applications. Bulk high temperature superconducting (HTS) materials can trap magnetic fields of magnitude over ten times higher than the maximum field produced by conventional magnets, which is limited practically to rather less than 2 T. In this paper, two large c-axis oriented, single-grain YBCO and GdBCO bulk superconductors are magnetized by the pulsed field magnetization (PFM) technique at temperatures of 40 and 65 K and the characteristics of the resulting trapped field profile are investigated with a view of magnetizing such samples as trapped field magnets (TFMs) in situ inside a trapped flux-type superconducting electric machine. A comparison is made between the temperatures at which the pulsed magnetic field is applied and the results have strong implications for the optimum operating temperature for TFMs in trapped flux-type superconducting electric machines. The effects of inhomogeneities, which occur during the growth process of single-grain bulk superconductors, on the trapped field and maximum temperature rise in the sample are modelled numerically using a 3D finite-element model based on the H-formulation and implemented in Comsol Multiphysics 4.3a. The results agree qualitatively with the observed experimental results, in that inhomogeneities act to distort the trapped field profile and reduce the magnitude of the trapped field due to localized heating within the sample and preferential movement and pinning of flux lines around the growth section regions (GSRs) and growth sector boundaries (GSBs), respectively. The modelling framework will allow further investigation of various inhomogeneities that arise during the processing of (RE)BCO bulk superconductors, including inhomogeneous Jc distributions and the presence of current-limiting grain boundaries and cracks, and it can be used to assist optimization of

Theory of the upper critical field in antiferromagnetic superconductors

International Nuclear Information System (INIS)

Ro, C.; Levin, K.

1984-01-01

We compute the temperature T dependence of the upper critical field H/sub c/2(T) in antiferromagnetic (AF) superconductors. Using a strong-coupling formalism we explicitly treat the effects of the molecular field H/sub Q/, inelastic and elastic spin-fluctuation scattering and magnetic as well as nonmagnetic impurities. A sum rule is used to relate the T dependence of H/sub Q/ to that of the spin-fluctuation scattering. The decreased pair breaking observed below the Neel temperature in SmRh 4 B 4 and the increased pair breaking seen in the AF Chevrel compounds will both occur in our theory for a reasonable choice of parameters. For larger values of the dimensionless spin-exchange coupling constant N(0)J/sup c/f, spin-fluctuation-scattering effects dominate over those of H/sub Q/ and decreased pair breaking is observed below T/sub N/. For smaller values of the coupling constant, the converse is true. Impurity scattering is treated in a self-consistent fashion. As a consequence, the molecular field H/sub Q/ is altered by nonmagnetic impurities. This leads to important pair-breaking effects in H/sub c/2. A physical manifestation of this pair breaking is a qualitative change in the shape of the H/sub c/2 versus T curve, as nonmagnetic impurities are added. We give detailed predictions for the expected effects of these impurities on H/sub c/2 which can be tested experimentally

Influence of kondo effect on the specific heat jump of anisotropic superconductors

Science.gov (United States)

Yoksan, S.

1986-01-01

A calculation for the specific heat jump of an anisotropic superconductor with Kondo impurities is presented. The impurities are treated within the Matsuura - Ichinose - Nagaoka framework and the anisotropy effect is described by the factorizable model of Markowitz and Kadanoff. We give explicit expressions for the change in specific heat jump due to anisotropy and impurities which can be tested experimentally.

Influence of Kondo effect on the specific heat jump of anisotropic superconductors

International Nuclear Information System (INIS)

Yoksan, S.

1986-01-01

A calculation for the specific heat jump of an anisotropic superconductor with Kondo impurities is presented. The impurities are treated within the Matsuura - Ichinose - Nagaoka framework and the anisotropy effect is described by the factorizable model of Markowitz and Kadanoff. Explicit expressions are given for the change in specific heat jump due to anisotropy and impurities which can be tested experimentally. (author)

Friction in levitated superconductors

International Nuclear Information System (INIS)

Brandt, E.H.

1988-01-01

A type I superconductor levitated above a magnet of low symmetry has a unique equilibrium position about which it may oscillate freely. In contrast, a type II superconductor has a continuous range of stable equilibrium positions and orientations where it floats rigidly without swinging or orbiting as if it were stuck in sand. A strong internal friction conspicuously indicates the existence and unpinning of flux lines in oxide superconductors levitated above liquid nitrogen. It is shown how these effects follow from the hysteretic magnetization curves and how the energy is dissipated

The low-field peak in magnetization loops of uniform and granular superconductors in perpendicular magnetic fields

Czech Academy of Sciences Publication Activity Database

Johansen, T. H.; Shantsev, D. V.; Koblischka, M. R.; Galperin, Y. M.; Nálevka, Petr; Jirsa, Miloš

341-348, - (2000), s. 1443-1444 ISSN 0921-4534. [International Conference on Materials and Mechanism of Superconductivity High Temperature Superconductors /4./. Houston , 20.02.2000-25.02.2000] Institutional research plan: CEZ:AV0Z1010914 Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.489, year: 2000

Field generated within the SSC magnets due to persistant currents in the superconductor

International Nuclear Information System (INIS)

Green, M.A.

1984-01-01

This report presents the results of a number of computer studies of the magnetic fields generated by persistent circulating currents in the superconductor of superconducting dipoles. These magnetic fields are referred to as residual fields throughout this report. Since the field generated by persistent currents have a hysteric behavior, they are analagous to the residual filed found in iron bound conventional solenoids. The residual field calculations presented in this report were done using the LBL SCMAG4 computer code. This code has not been well tested against measured data, but a comparison with measured CBA data given in this report suggests that good agreement is possible. The residual fields generated by persistent superconducting currents are rich in higher multipoles. This is of concern to the accelerator designer for SSC. This report shows the effect of various superconductor parameters and coil parameters on the magnitude and structure of the residual fields. The effect of the magnet charging history on residual fields is aldo discussed. 14 references

Incommensurate magnetic modulations in the magnetic superconductor HoNi2B2C

International Nuclear Information System (INIS)

Schneider, M.; Zaharko, O.; Keller, L.; Allenspach, P.; Kreyssig, A.; Canfield, P.C.

2006-01-01

Full text: The borocarbide HoNi 2 B 2 C is an unconventional superconductor of particular interest, since long-range magnetism coexists and competes with superconductivity on a common energy range [1]. Our study is based on high quality single crystals of 11 B-substituted HoNi 2 B 2 C. The neutron diffraction investigations are devoted to two issues of specific relevance to HoNi 2 B 2 C. Firstly, the near re-entrant phase between 5K 2 B 2 C is more complicated than proposed so fare [2]. Furthermore we performed a spherical neutron polarimetry experiment to determine the two ICM magnetic structures of HoNi 2 B 2 C and neutron spectroscopy investigations to obtain the microscopic magnetic coupling parameters. All these studies resulted in quite a consistent and complete picture of magnetism in HoNi 2 B 2 C, however, we could not find clear evidence for a strong interaction between superconductivity and magnetism. (author)

A Double-Decker Levitation Experiment Using a Sandwich of Superconductors.

Science.gov (United States)

Jacob, Anthony T.; And Others

1988-01-01

Shows that the mutual repulsion that enables a superconductor to levitate a magnet and a magnet to levitate a superconductor can be combined into a single demonstration. Uses an overhead projector, two pellets of "1-2-3" superconductor, Nd-Fe-B magnets, liquid nitrogen, and paraffin. Offers superconductor preparation, hazards, and disposal…

The effect of ac magnetic fields on the lifting power of levitating superconductors

International Nuclear Information System (INIS)

Smolyak, B M; Ermakov, G V; Chubraeva, L I

2007-01-01

This study deals with the decrease in the levitation force under the action of an ac field up to the frequency at which oscillations of the superconducting suspension are limited by inertia. The lifting force was measured as a function of the ac field amplitude and the exposure time. It was shown that the force quickly decreased at the moment the ac field was applied and then continued diminishing, but at a lower rate. A qualitative model was proposed, taking into account two effects of the ac field on the magnetization of the levitating superconductor: a complete destruction of the critical state in some section of the superconductor (to a depth λ ac ) and the initiation of a faster magnetic relaxation in the region where the induction gradient is preserved

Electromagnetic response of non-trivially shaped superconductors in external magnetic fields and with applied currents

International Nuclear Information System (INIS)

Cabral, Leonardo Ribeiro Eulalio; Aguiar, Jose Albino Oliveira de

2002-01-01

Full text: The study of the electromagnetic response of high-T c superconductors is essential for future technological applications. Such materials are hard type II superconductors, where the mixed state (a state characterized by quantized normal flux tubes - also called vortices - immersed in a superconductor phase) occupies most of the phase diagram. Therefore, the electromagnetic properties are dictated by the vortex dynamics in these materials. One has also to consider the presence of structural defects and thermal effects, which turn the vortex dynamics very complex. These difficulties may be overcome throughout a macroscopic description, also known as continuum approximation, of the electromagnetic fields in superconductors, obtained from critical state models and constitutive relations E = E(j) and H = H(B) (where E is the electric field generated by moving vortices, j the current density, B the induction - related to the local density of vortices - and H the reversible magnetic field that is in equilibrium with B). In superconductors with negligible demagnetization factors, such as long cylinders and bars with applied magnetic fields and/or currents along their longer dimensions, the Meissner state and the flux penetration is quite well understood. However, the actual specimen shape plays an important role on the electromagnetic behavior of superconductors. Numerical methods are often employed, since such cases are hard to treat analytically. In this work we studied the electromagnetic response of superconductors with various shapes. The Meissner state is obtained for thin curved strips and long cylinders with arbitrary cross-section, in perpendicular field and with applied currents. The flux penetration is numerically calculated for thin curved strips for the Bean (j c =const.) and the Kim (j c (B) = j c0 /(1 + βB)) models. (author)

The new Fe-based superconductors

International Nuclear Information System (INIS)

Mao, Zhiqiang

2011-01-01

The discovery of unconventional superconductivity in doped iron pnictides has ushered in a new era of high temperature superconductivity. The superconductivity of these materials occurs in close proximity to magnetic instability; superconductivity is achieved by suppressing a long-range antiferromagnetic (AFM) order through charge carrier doping or pressure. In this talk, I will first give a brief overview of the phase diagrams of iron-based superconductors, and then talk about our recent research on iron chalcogenide Fe 1+y (Te 1-x Se x ) superconductors, which is structurally the simplest of the Fe-based superconductors. Although the Fermi surface of iron chalcogenides is similar to iron pnictides, the parent compound Fe 1+y Te exhibits AFM order with in-plane magnetic wave-vector (π, 0). This contrasts the pnictide parent compounds where the magnetic order has an in-plane magnetic wave-vector (π, π) that connects hole and electron parts of the Fermi surface. Despite these differences, both the pnictide and chalcogenide Fe-superconductors exhibit superconducting spin resonances around (π, π), suggesting a common symmetry for their superconducting order parameter. A central question in this burgeoning field is therefore how (π, π) superconductivity can emerge from a (π, 0) magnetic instability. I will address this issue in my talk. I will show the phase diagram of electronic and magnetic properties we recently established for this system and discuss the relationship between magnetic coupling and electronic properties. Our results reveal that the magnetic soft mode evolving from the (π, 0)-type magnetic long-range order is associated with weak charge carrier localization. Bulk superconductivity occurs only as magnetic correlations near (π, 0) are strongly suppressed and the magnetic mode at (π, π) becomes dominant; this suggests a common magnetic origin for superconductivity in iron chalcogenide and pnictide superconductors. (author)

Design of Nb$_{3}$Sn magnetic devices to study the superconductor degradation under variable mechanical load

CERN Document Server

Regis, Federico

2009-01-01

The Large Hadron Collider (LHC) is a two-ring, superconducting synchrotron accelerator and collider installed in a 27 km long tunnel aiming at the discovery of the Higgs particle and the study of rare events with center mass collision energies of up to 14 TeV. The number of collisions per unit of area and time in a collider are evaluated trough the Luminosity function. Inside the LHC, superconducting magnets aligned with a precision of a few tenths of millimeters are used to bend and focus the particle trajectories. The LHC can be considered as the state of the art for superconducting magnets using the Nb-Ti superconductor technology. Therefore, a higher luminosity and beam energy can be achieved in the LHC only by using a more performing superconductor, such as the Nb$_{3}$Sn. This is considered as the most suitable superconductor to be used in high field magnets, allowing peak field of the order of 15 T. Nevertheless, the critical current jc variations in a Nb$_{3}$Sn has been found as strongly dependent on...

Magnetic hyperfine field at a Cd impurity diluted in RCo{sub 2} at finite temperatures

Energy Technology Data Exchange (ETDEWEB)

Oliveira, A.L. de, E-mail: alexandre.oliveira@ifrj.edu.br [Instituto Federal de Educação, Ciência e Tecnologia do Rio de Janeiro, Campus Nilópolis – RJ (Brazil); Chaves, C.M., E-mail: cmch@cbpf.br [Centro Brasileiro de Pesquisas Físicas, Rio de Janeiro (Brazil); Oliveira, N.A. de [Instituto de Física Armando Dias Tavares, Universidade do Estado do Rio de Janeiro, Rio de Janeiro (Brazil); Troper, A. [Centro Brasileiro de Pesquisas Físicas, Rio de Janeiro (Brazil)

2015-06-15

The local magnetic moments and the magnetic hyperfine fields at an s–p Cd impurity diluted in inter-metallic Laves phase compounds RCo{sub 2} (R=Gd, Tb) at finite temperatures are calculated. For other rare earth elements (light or heavy) the pure compounds display a magnetic first order transition and are not describable by our formalism. The host has two coupled lattices (R and Co) both having itinerant d electrons but only the rare earth lattice has localized f electrons. They all contribute to the magnetization of the host and also to the local moment and to the magnetic hyperfine field at the impurity. The investigation of magnetic hyperfine field in these materials then provides valuable information on the d-itinerant electrons and also on the localized (4f) magnetic moments. For the d–d electronic interaction we use the Hubbard–Stratonovich identity thus allowing the employment of functional integral in the static saddle point approximation. Our model reproduces quite well the experimental data. - Highlights: • A functional integral method in the static limit, producing site disorder, is used. • The site disorder is treated with the coherent potential approximation (CPA) • A Friedel sum rule gives a self-consistency condition for the impurity energy. • The experimental curve of hyperfine fields×temperature is very well reproduced.

Disorder and non-linear magnetic response of high Tc superconductors

Energy Technology Data Exchange (ETDEWEB)

Burin, J.P. (Lab. de Physique des Solides, INSA, 35 - Rennes (France)); Fouad, Y. (Lab. de Physique des Solides, INSA, 35 - Rennes (France)); Raboutou, A. (Lab. de Physique des Solides, INSA, 35 - Rennes (France)); Peyral, P. (Lab. de Physique des Solides, INSA, 35 - Rennes (France)); Lebeau, C. (Lab. de Physique des Solides, INSA, 35 - Rennes (France)); Rosenblatt, J. (Lab. de Physique des Solides, INSA, 35 - Rennes (France)); Mokhtari, M. (Lab. de Chimie du Solide et inorganique Moleculaire, Univ. Rennes 1, 35 (France)); Pena, O. (Lab. de Chimie du Solide et inorganique Moleculaire, Univ. Rennes 1, 35 (France)); Perrin, C. (Lab. de Chimie du Solide et inorganique Moleculaire, Univ. Rennes 1, 35 (France))

1993-05-10

We measure the low frequency magnetic response of YBa[sub 2]Cu[sub 3]O[sub 6.7]F[sub x] (0 [<=] x < 0.2) ceramics in a wide range of a.c. fields (10[sup -7] T [<=] [mu][sub 0]H[sub 0] [<=] 10[sup -4]). When changing the amount of disorder (varying x) on the microscopic level we find the same non linear response with field amplitude H[sub 0] as in granular conventional superconductors. The real part of the susceptibility appears as a universal function of H[sub 1](T)/H[sub 0] where H[sub 1](T) is the field of first flux penetration. The power law dependence found for H[sub 1](T) can be understood in the framework of the coherence transition of granular superconductors with random couplings. (orig.)

The influence of impurity concentration and magnetic fields on the superconducting transition of high-purity titanium

Energy Technology Data Exchange (ETDEWEB)

Peruzzi, A.; Gottardi, E.; Peroni, I.; Ponti, G.; Ventura, G

1999-08-01

The influence of impurity concentration c and applied magnetic field H on the superconducting transition of high-purity commercial titanium samples was investigated. The superconductive transition temperature T{sub C} was found to be very sensitive to the impurity concentration (dT{sub C}/dc {approx} -0.6 mK/w.ppm) and to the applied magnetic field (dT{sub C}/dH {approx} -1.1 mK/G). A linear dependence of T{sub C} decrease on impurity concentration, as theoretically predicted by various authors, was observed. In the purest sample, a linear decrease of T{sub C} on the applied magnetic field was found. The run-to-run and sample-to-sample reproducibility of the transition of the same sample was evaluated, and its suitability as a thermometric reference point below 1 K was discussed.

Electromagnetic field analyses of two-layer power transmission cables consisting of coated conductors with magnetic and non-magnetic substrates and AC losses in their superconductor layers

International Nuclear Information System (INIS)

Nakahata, Masaaki; Amemiya, Naoyuki

2008-01-01

Two-dimensional electromagnetic field analyses were undertaken using two representative cross sections of two-layer cables consisting of coated conductors with magnetic and non-magnetic substrates. The following two arrangements were used for the coated conductors between the inner and outer layers: (1) tape-on-tape and (2) alternate. The calculated magnetic flux profile around each coated conductor was visualized. In the case of the non-magnetic substrate, the magnetic field to which coated conductors in the outer layer are exposed contains more perpendicular component to the conductor wide face (perpendicular field component) when compared to that in the inner layer. On the other hand, for the tape-on-tape arrangement of coated conductors with a magnetic substrate, the reverse is true. In the case of the alternate arrangement of the coated conductor with a magnetic substrate, the magnetic field to which the coated conductors in the inner and outer layers are exposed experiences a small perpendicular field component. When using a non-magnetic substrate, the AC loss in the superconductor layer of the coated conductors in the two-layer cables is dominated by that in the outer layer, whereas the reverse is true in the case of a magnetic substrate. When comparing the AC losses in superconductor layers of coated conductors with non-magnetic and magnetic substrates in two-layer cables, the latter is larger than the former, but the influence of the magnetism of substrates on AC losses in superconductor layers is not remarkable

Magnetic excitations in the heavy-Fermion superconductor URu2Si2

DEFF Research Database (Denmark)

Broholm, C.; Lin, H.; Matthews, P.T.

1991-01-01

Antiferromagnetic order and fluctuations in the heavy-fermion superconductor URu2Si2 have been studied by magnetic neutron scattering. Below T(N) = 17.5 K, URu2Si2 is a type-I antiferromagnet with an anomalously small ordered moment of (0.04 +/- 0.01)mu-B polarized along the tetragonal c axis...

Superconductors with low critical temperature for electro-magnets

International Nuclear Information System (INIS)

Devred, A.

2002-07-01

Among the superconductors with low critical temperature that are used to build magnets, NbTi has reached a development state that allows a massive production for big equipment of physics and an industrial production in the domain of medicine imaging. The material that might challenge the supremacy of NbTi is Nb 3 Sn but some technical difficulties have yet to be overcome. This report begins with a review of the different industrial processes used to produce superconducting wires based on the NbTi and Nb 3 Sn materials. The transition from the superconducting state to the resistive normal state is described for both materials, the magnetizing of multi-wire superconducting cables is also presented. The author details the different patterns of wires in cables and proposes a formulary that allows the determination, in some simple cases,of energy losses that are generated in a superconducting cable by a variable magnetic field. (A.C.)

Magnetism without magnetic impurities in oxides ZrO.sub.2./sub. and TiO.sub.2./sub..

Czech Academy of Sciences Publication Activity Database

Máca, František; Kudrnovský, Josef; Drchal, Václav; Bouzerar, G.

2008-01-01

Roč. 88, 18-20 (2008), s. 2755-2764 ISSN 1478-6435 R&D Projects: GA ČR GA202/07/0456; GA MŠk OC 150; GA AV ČR IAA100100616 Institutional research plan: CEZ:AV0Z10100520 Keywords : magnetism * impurity * oxides * density functional calculations Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.384, year: 2008

Distribution of magnetic field in type II superconductors

International Nuclear Information System (INIS)

Castro, J.L. de.

1986-09-01

The magnetie field penetration profile, in type II superconductor, has studied in specially designed cylindrical samples. The samples consist of alternated thick layers ( > 30 μm ) of niobium and copper deposited, by electron-beam evaporation or electro-chemical deposition, on cylindric core of either niobium or copper. The magnetization curves, the magnetic susceptibility and the differential susceptibility for small hysteresis loop ( H c1 c2 ) were measured for all the samples between 4. 2 and 9.5 K. These measurements, done with flux pinned and without, show some peculiar descontinuities and inflections which seems to resemble the samples shape. A simple phenonenological extension of Bean's critical state model was applied to these results, giving a resonable qualitative agreement. Also, a more elaborated theoretical model was improve which could give more quantitative fitting. (author) [pt

Nematicity and Magnetism in FeSe and Other Families of Fe-Based Superconductors

Directory of Open Access Journals (Sweden)

Youichi Yamakawa

2016-06-01

Full Text Available Nematicity and magnetism are two key features in Fe-based superconductors, and their interplay is one of the most important unsolved problems. In FeSe, the magnetic order is absent below the structural transition temperature T_{str}=90  K, in stark contrast to the fact that the magnetism emerges slightly below T_{str} in other families. To understand such amazing material dependence, we investigate the spin-fluctuation-mediated orbital order (n_{xz}≠n_{yz} by focusing on the orbital-spin interplay driven by the strong-coupling effect, called the vertex correction. This orbital-spin interplay is very strong in FeSe because of the small ratio between the Hund’s and Coulomb interactions (J[over ¯]/U[over ¯] and large d_{xz}, d_{yz}-orbital weight at the Fermi level. For this reason, in the FeSe model, the orbital order is established irrespective of the fact that the spin fluctuations are very weak, so the magnetism is absent below T_{str}. In contrast, in the LaFeAsO model, the magnetic order appears just below T_{str} both experimentally and theoretically. Thus, the orbital-spin interplay due to the vertex correction is the key ingredient in understanding the rich phase diagram with nematicity and magnetism in Fe-based superconductors in a unified way.

Macroscopic theory of superconductors

International Nuclear Information System (INIS)

Carr, W.J. Jr.

1981-01-01

A macroscopic theory for bulk superconductors is developed in the framework of the theory for other magnetic materials, where ''magnetization'' current is separated from ''free'' current on the basis of scale. This contrasts with the usual separation into equilibrium and nonequilibrium currents. In the present approach magnetization, on a large macroscopic scale, results from the vortex current, while the Meissner current and other surface currents are surface contributions to the Maxwell j. The results are important for the development of thermodynamics in type-II superconductors. The advantage of the description developed here is that magnetization becomes a local concept and its associated magnetic field can be given physical meaning

Experimental Set-Up for Evaluation of Electro-Magnetic Characteristics of High-Tc Superconductors Cooled by Liquid Hydrogen

OpenAIRE

Shirai, Yasuyuki; Hikawa, Kyosuke; Shiotsu, Masahiro; Tatsumoto, Hideki; Hata, Koichi; Kobayashi, Hiroaki; Nonaka, Satoshi; Naruo, Yoshihiro; Inatani, Yoshifumi

2013-01-01

Liquid hydrogen (LH2) has excellent properties as a coolant, such as large latent heat, low viscosity coefficient, etc. Not only MgB2 but also other high-Tc superconductors are expected to have excellent properties when cooled by LH2. It is necessary for a stability design of a high-Tc superconductor cooled by LH2 to make an electro-magnetic characteristic clear. However, due to the handling difficulties of LH2, there are only few papers on the properties of LH2-cooled superconductors, especi...

Prospects of High Temperature Superconductors for fusion magnets and power applications

International Nuclear Information System (INIS)

Fietz, Walter H.; Barth, Christian; Drotziger, Sandra; Goldacker, Wilfried; Heller, Reinhard; Schlachter, Sonja I.; Weiss, Klaus-Peter

2013-01-01

Highlights: • An overview of HTS application in fusion is given. • BSCCO application for current leads is discussed. • Several approaches to come to a high current HTS cable are shown. • Open issues and benefits of REBCO high current HTS cables are discussed. -- Abstract: During the last few years, progress in the field of second-generation High Temperature Superconductors (HTS) was breathtaking. Industry has taken up production of long length coated REBCO conductors with reduced angular dependency on external magnetic field and excellent critical current density jc. Consequently these REBCO tapes are used more and more in power application. For fusion magnets, high current conductors in the kA range are needed to limit the voltage during fast discharge. Several designs for high current cables using High Temperature Superconductors have been proposed. With the REBCO tape performance at hand, the prospects of fusion magnets based on such high current cables are promising. An operation at 4.5 K offers a comfortable temperature margin, more mechanical stability and the possibility to reach even higher fields compared to existing solutions with Nb 3 Sn which could be interesting with respect to DEMO. After a brief overview of HTS use in power application the paper will give an overview of possible use of HTS material for fusion application. Present high current HTS cable designs are reviewed and the potential using such concepts for future fusion magnets is discussed

pi-phase magnetism in ferromagnetic-superconductor superlattices

CERN Document Server

Khusainov, M G; Proshin, Y N

2001-01-01

The Larkin-Ovchinnikov-Fylde-Ferrel new 0 pi- and pi pi-states are forecasted for the ferromagnetic metal/superconductor superlattices with antiferromagnetic magnetization orientation in the neighbouring layers. The above-mentioned states are characterized under certain conditions by higher critical temperature T sub c as compared to the earlier known LOFF 00- and pi 0-states with the FM-layers ferromagnetic ordering. It is shown that the nonmonotonous behavior of the T sub c of the FM/S superlattices by the thickness of the S-layers lower than the d sub s suppi value is connected with the cascades of the 0 pi-pi pi-0 pi phase transitions. The character of the T sub c oscillations by the d sub s > d sub s suppi is related to the 00-pi 0-00 transitions. The logical elements of the new type, combining the advantages of the superconducting and magnetic information recording in one sample are proposed on the basis of the FM/S superlattices

Magnetic properties of metallic impurities with strongly correlated electrons

Czech Academy of Sciences Publication Activity Database

Janiš, Václav; Ringel, Matouš

2009-01-01

Roč. 115, č. 1 (2009), s. 30-35 ISSN 0587-4246 R&D Projects: GA ČR GA202/07/0644 Institutional research plan: CEZ:AV0Z10100520 Keywords : And erson impurity * strong electron correlations * spin-polarized solution * three-channel parquet equations * magnetic field Subject RIV: BE - Theoretical Physics Impact factor: 0.433, year: 2009 http://przyrbwn.icm.edu.pl/APP/ABSTR/115/a115-1-5.html

Influence of soft ferromagnetic sections on the magnetic flux density profile of a large grain, bulk Y–Ba–Cu–O superconductor

International Nuclear Information System (INIS)

Philippe, M P; Wéra, L; Fagnard, J-F; Vanderheyden, B; Vanderbemden, P; Ainslie, M D; Dennis, A R; Shi, Y-H; Cardwell, D A

2015-01-01

Bulk, high temperature superconductors have significant potential for use as powerful permanent magnets in a variety of practical applications due to their ability to trap record magnetic fields. In this paper, soft ferromagnetic sections are combined with a bulk, large grain Y–Ba–Cu–O high temperature superconductor to form superconductor/ferromagnet hybrid structures. We study how the ferromagnetic sections influence the shape of the profile of the trapped magnetic induction at the surface of each structure and report the surface magnetic flux density measured by Hall probe mapping. These configurations have been modelled using a 2D axisymmetric finite element method based on the H-formulation and the results show excellent qualitative and quantitative agreement with the experimental measurements. The model has also been used to study the magnetic flux distribution and predict the behaviour for other constitutive laws and geometries. The results show that the ferromagnetic material acts as a magnetic shield, but the flux density and its gradient are enhanced on the face opposite to the ferromagnet. The thickness and saturation magnetization of the ferromagnetic material are important and a characteristic ferromagnet thickness d* is derived: below d*, saturation of the ferromagnet occurs, and above d*, a weak thickness-dependence is observed. The influence of the ferromagnet is observed even if its saturation magnetization is lower than the trapped flux density of the superconductor. Conversely, thin ferromagnetic discs can be driven to full saturation even though the outer magnetic field is much smaller than their saturation magnetization. (paper)

Magnetic tunable confinement of the superconducting condensate in superconductor/ferromagnet hybrids

International Nuclear Information System (INIS)

Aladyshkin, A.Yu.; Gillijns, W.; Silhanek, A.V.; Moshchalkov, V.V.

2008-01-01

The effect of a nonuniform magnetic field induced by a ferromagnet on the magnetoresistance of thin-film superconductor/ferromagnet hybrid structures was investigated experimentally. Two different magnetic textures with out-of-plane magnetization were considered: a plain ferromagnetic film with bubble domains and a regular array of ferromagnetic dots. The stray fields of the structures are able to affect the spatial profile of the superconducting condensate, leading to a modification of the dependence of the critical temperature T c on an external magnetic field H. We showed how the standard linear T c (H) dependence with a single maximum at H=0 can be continuously transformed into so-called reentrant phase boundary with two T c peaks. We demonstrated that both domain-wall superconductivity and field-induced superconductivity are different manifestations of the magnetic confinement effect in various magnetic patterns

Calculation of the magnetic flux density distribution in type-II superconductors with finite thickness and well-defined geometry

International Nuclear Information System (INIS)

Forkl, A.; Kronmueller, H.

1995-01-01

The distribution of the critical current density j c (r) in hard type-II superconductors depends strongly on their sample geometry. Rules are given for the construction of j c (r). Samples with homogeneous thickness are divided into cakelike regions with a unique current direction. The spatial magnetic flux density distribution and the magnetic polarization of such a cakelike unit cell with homogeneous current density are calculated analytically. The magnetic polarization and magnetic flux density distribution of a superconductor in the mixed state is then given by an adequate superposition of the unit cell solutions. The theoretical results show good agreement with magneto-optically determined magnetic flux density distributions of a quadratic thin superconducting YBa 2 Cu 3 O 7-x film. The current density distribution is discussed for several sample geometries

Measurement of the magnetic field inside the holes of a drilled bulk high-Tc superconductor

Science.gov (United States)

Lousberg, Gregory P.; Fagnard, Jean-François; Noudem, Jacques G.; Ausloos, Marcel; Vanderheyden, Benoit; Vanderbemden, Philippe

2009-04-01

We use macroscopic holes drilled in a bulk YBCO superconductor to probe its magnetic properties in the volume of the sample. The sample is subjected to an AC magnetic flux with a density ranging from 30 to 130 mT and the flux in the superconductor is probed by miniature coils inserted in the holes. In a given hole, three different penetration regimes can be observed: (i) the shielded regime, where no magnetic flux threads the hole; (ii) the gradual penetration regime, where the waveform of the magnetic field has a clipped sine shape whose fundamental component scales with the applied field; and (iii) the flux concentration regime, where the waveform of the magnetic field is nearly a sine wave, with an amplitude exceeding that of the applied field by up to a factor of two. The distribution of the penetration regimes in the holes is compared with that of the magnetic flux density at the top and bottom surfaces of the sample, and is interpreted with the help of optical polarized light micrographs of these surfaces. We show that the measurement of the magnetic field inside the holes can be used as a local characterization of the bulk magnetic properties of the sample.

Effect of axial strain on the critical current of Ag-sheathed Bi-based superconductors in magnetic fields up to 25 T

International Nuclear Information System (INIS)

Ekin, J.W.; Finnemore, D.K.; Li, Q.; Tenbrink, J.; Carter, W.

1992-01-01

The irreversible strain limit ε irrev for the onset of permanent axial strain damage to Ag-sheathed Bi 2 Sr 2 Ca 1 Cu 2 O 8+x and Bi 2 Sr 2 Ca 2 Cu 3 O 10+x superconductors has been measured to be in the range of 0.2%--0.35%. This strain damage onset is about an order of magnitude higher than for bulk sintered Y-, Bi-, or Tl-based superconductors and is approaching practical values for magnet design. The measurements show that the value of ε irrev is not dependent on magnetic field, nor does the critical current depend on strain below ε irrev at least up to 25 T at 4.2 K. Both of these factors indicate that the observed strain effect in Ag-sheathed Bi-based superconductors is not intrinsic to the superconductor material. Rather, the effect is extrinsic and arises from superconductor fracture. Thus, the damage onset is amenable to further enhancement. Indeed, the data suggest that subdividing the superconductor into fine filaments or adding Ag to the superconductor powder prior to processing significantly enhances the damage threshold ε irrev to above 0.6%

The fluctuation Hall conductivity and the Hall angle in type-II superconductor under magnetic field

Energy Technology Data Exchange (ETDEWEB)

Tinh, Bui Duc, E-mail: tinhbd@hnue.edu.vn [Institute of Research and Development, Duy Tan University, K7/25 Quang Trung, Danang (Viet Nam); Department of Physics, Hanoi National University of Education, 136 Xuan Thuy, Cau Giay, Hanoi (Viet Nam); Hoc, Nguyen Quang; Thu, Le Minh [Department of Physics, Hanoi National University of Education, 136 Xuan Thuy, Cau Giay, Hanoi (Viet Nam)

2016-02-15

Highlights: • The time-dependent Ginzburg–Landau was used to calculate fluctuation Hall conductivity and Hall angle in type-II superconductor in 2D and 3D. • We obtain analytical expressions for the fluctuation Hall conductivity and the Hall angle summing all Landau levels without need to cutoff higher Landau levels to treat arbitrary magnetic field. • The results were compared to the experimental data on YBCO. - Abstract: The fluctuation Hall conductivity and the Hall angle, describing the Hall effect, are calculated for arbitrary value of the imaginary part of the relaxation time in the frame of the time-dependent Ginzburg–Landau theory in type II-superconductor with thermal noise describing strong thermal fluctuations. The self-consistent Gaussian approximation is used to treat the nonlinear interaction term in dynamics. We obtain analytical expressions for the fluctuation Hall conductivity and the Hall angle summing all Landau levels without need to cutoff higher Landau levels to treat arbitrary magnetic field. The results are compared with experimental data on high-T{sub c} superconductor.

Impurity scattering effect on charge transport in high-Tc cuprate junctions

International Nuclear Information System (INIS)

Tanaka, Y.; Asano, Y.; Kashiwaya, S.

2004-01-01

It is known that the zero-bias conductance peak (ZBCP) is expected in tunneling spectra of normal-metal/high-Tc cuprate junctions because of the formation of the midgap Andreev resonant states (MARS) at junction interfaces. In the present review, we report the recent theoretical study of impurity scattering effects on the tunneling spectroscopy. In the former part of the present paper, we discuss impurity effects in normal metal. We calculate tunneling conductance for diffusive normal metal (DN)/high Tc cuprate junctions based on the Keldysh Green's function technique. Besides the ZBCP due to the MARS, we can expect ZBCP caused by the different origin, i.e., the coherent Andreev reflection (CAR) assisted by the proximity effect in DN. Their relative importance depends on the angle a between the interface normal and the crystal axis of high-Tc superconductors. At α = 0, we find the ZBCP by the CAR for low transparent junctions with small Thouless energies in DN; this is similar to the case of diffusive normal metal/insulator/s-wave superconductor junctions. Under increase of α from zero to π/4, the contribution of MARS to ZBCP becomes more prominent and the effect of the CAR is gradually suppressed. Such complex spectral features would be observable in conductance spectra of high-Tc junctions at very low temperatures. In the latter part of our paper, we study impurity effects in superconductors. We consider impurities near the junction interface on the superconductor side. The conductance is calculated from the Andreev and the normal reflection coefficients which are estimated by using the single-site approximation in an analytic calculation and by the recursive Green function method in a numerical simulation. We find splitting of the ZBCP in the presence of the time reversal symmetry. Thus the zero-field splitting of ZBCP in the experiment does not perfectly prove an existence of broken time reversal symmetry state

On the interplay of superconductivity and magnetism

International Nuclear Information System (INIS)

Powell, Benjamin James

2002-01-01

We explore the exchange field dependence of the Hubbard model with a attractive, effective, pairwise, nearest neighbour interaction via the Hartree-Fock-Gorkov approximation. We derive a Ginzburg-Landau theory of spin triplet superconductivity in an exchange field. For microscopic parameters which lead to ABM phase superconductivity in zero field, the Ginzburg-Landau theory allows both an axial (A, A 1 or A 2 ) solution with the vector order parameter, d(k), perpendicular to the field, H, and an A phase solution with d(k) parallel to H. We study the spin-generalised Bogoliubov-de Gennes (BdG) equations for this model with parameters suitable for strontium ruthenate (Sr 2 RuO 4 ). The A 2 phase is found to be stable in a magnetic field. However, in the real material, spin-orbit coupling could pin the order parameter to the crystallographic c-axis which would favour the A phase for fields parallel to the c-axis. We show that the low temperature thermodynamic behaviour in a magnetic field could experimentally differentiate between these two possible behaviours. Further we show that this pinning could cause a Freedericksz (Frederiks) transition in bulk Sr 2 RuO 4 (Freedericksz transitions have only previously been seen in confined geometries.) We calculate the superconducting critical temperature, T C , of ZrZn 2 in the presence of non-magnetic impurity scattering from the Abrikosov-Gorkov formula. Residual resistivity experiments indicate that the transition temperature in the absence of impurity scattering, T CO = 1.15 ± 0.15 K, while de Haas-van Alphen experiments give T CO ∼ 3 K. We discuss this disagreement and conclude that the former estimate is the more reliable. We derive the equal spin pairing (ESP) gap equations for a ferromagnetic superconductor, which we solve for parameters chosen for ZrZn 2 . We show that for ESP states in a ferromagnetic superconductor, in the absence of spin flip processes, the two spin states are separate subsystems due to exchange

The effect of magnet size on the levitation force and attractive force of single-domain YBCO bulk superconductors

International Nuclear Information System (INIS)

Yang, W M; Chao, X X; Bian, X B; Liu, P; Feng, Y; Zhang, P X; Zhou, L

2003-01-01

The levitation forces between a single-domain YBCO bulk and several magnets of different sizes have been measured at 77 K to investigate the effect of the magnet size on the levitation force. It is found that the levitation force reaches a largest (peak) value when the size of the magnet approaches that of the superconductor when the other conditions are fixed. The absolute maximum attractive force (in the field-cooled state) increases with the increasing of the magnet size, and is saturated when the magnet size approaches that of the superconductor. The maximum attractive force in the field-cooled (FC) state is much higher than that of the maximum attractive force in the zero field-cooled (ZFC) state. The results indicate that the effects of magnetic field distribution on the levitation force have to be considered during the designing and manufacturing of superconducting devices

Effects of glucose doping on the MgB{sub 2} superconductors using cheap crystalline boron

Energy Technology Data Exchange (ETDEWEB)

Parakkandy, Jafar Meethale [Department of Physics and Astronomy, College of Science, PO Box 2455, King Saud University, Riyadh 11451,Saudi Arabia (Saudi Arabia); Shahabuddin, Mohammed, E-mail: mshahab@ksu.edu.sa [Department of Physics and Astronomy, College of Science, PO Box 2455, King Saud University, Riyadh 11451,Saudi Arabia (Saudi Arabia); Shah, M. Shahabuddin; Alzayed, Nasser S.; Qaid, Salem A.S.; Madhar, Niyaz Ahmad; Ramay, Shahid M. [Department of Physics and Astronomy, College of Science, PO Box 2455, King Saud University, Riyadh 11451,Saudi Arabia (Saudi Arabia); Shar, Muhammad Ali [Mechanical Engineering Department, College of Engineering, P.O. Box 800, King Saud University, Riyadh 11421 (Saudi Arabia)

2015-12-15

Highlights: • First report on glucose doped MgB{sub 2} superconductor by single step dry mixing approach. • Cheap crystalline boron used for the sample preparation. • Microstructure and superconducting properties of the superconductors are discussed. • Less degradation in low field critical current density observed. • MgB{sub 2} with 2 at. % glucose doped showed the highest J{sub c}, ≈ 2 × 10{sup 4}A/cm{sup 2} for 20 K at 3 T. - Abstract: We report the effect of glucose (C{sub 6}H{sub 12}O{sub 6}) doping on the structural and electromagnetic properties of MgB{sub 2} superconductor fabricated by dry mixing using planetary ball milling. Herein, as-prepared bulk polycrystalline Mg (B{sub 1–x}C{sub x}) {sub 2} samples with different doping levels (x = 0, 2, 4, and 6 at. %) were systematically studied by X-ray diffraction, magnetic and resistivity measurements, and microstructure analysis. When carbon doped, the reduction in critical transition temperature and shrinkage in a-lattice were obviously observed. This resulted in structural distortion of the MgB{sub 2} lattice, and thereby, enhanced an impurity scattering. In addition to these, upper critical field and high-field critical current densities were also enhanced. On the other hand, both pinning force and low-field critical current density are decreased. The high field enhancement and low field degradation are due to increase in impurity scattering and decrease in pinning force respectively.

Magneto-optical imaging of magnetic flux distribution in high-Tc superconductors

International Nuclear Information System (INIS)

Ueno, K.; Murakamia, H.; Kawayama, I.; Doda, Y.; Tonouchi, M.; Chikumoto, N.

2004-01-01

Prototype systems of home-made magneto-optical microscopes were fabricated, and preliminary studies were carried out using Bi 2 Sr 2 CaCu 2 O 8+δ single crystals and an YBa 2 Cu 3 O 7-δ superconductor vortex flow transistor. In the study using BSCCO crystals, we succeeded in the observation of magnetic flux penetration into half-peeled thin flake region on the crystal surface, and it was found that the magnetic fluxes penetrate in characteristic one-dimensional alignment almost along the crystal a-axis. On the other hand, in the study using the YBCO device clear changes in the generated magnetic field distribution could be detected corresponding to the current direction

Magnetic levitation on a type-I superconductor as a practical demonstration experiment for students

OpenAIRE

Osorio, M. R.; Lahera, D. E.; Suderow, H.

2012-01-01

We describe and discuss an experimental set-up which allows undergraduate and graduate students to view and study magnetic levitation on a type-I superconductor. The demonstration can be repeated many times using one readily available 25 liter liquid helium dewar. We study the equilibrium position of a magnet that levitates over a lead bowl immersed in a liquid hand-held helium cryostat. We combine the measurement of the position of the magnet with simple analytical calculations. This provide...

Levitation force and magnetization in bulk and thin film high Tc superconductors

International Nuclear Information System (INIS)

Riise, A.B

1998-04-01

The authors present high-resolution measurements of the repulsive vertical force and its associated stiffness between a Nd-B-Fe magnet and a YBa 2 Cu 3 O 7-δ superconductor in cylindrical geometry. The results are compared with theoretical predictions. The calculations are based on a model in which the superconductor is assumed to be either a sintered granular material or consisting of grains embedded in a nonactive matrix so that only intragranular currents are important. The critical state model is applied to each grain individually and closed form expressions for both vertical force F z and stiffness are obtained in a configuration with cylindrical symmetry. The model explains all features of the experimental results in a consistent way. A good quantitative agreement has been obtained using only three adjustable parameters. Several central aspects of the phenomenon of magnetic levitation with high-T c superconductors are presented. High-resolution measurements are made of the repulsive vertical force and its associated stiffness as well as the horizontal stabilizing force and the stiffness governing lateral vibrations. The results obtained at 77 K using a granular YBa 2 Cu 3 O 7-δ sample and Nd-Fe-B magnet in a rectangular levitation configuration are compared with theoretical predictions. The calculations, which are based on the critical state model with the assumption that it applies to the grins individually, give closed-form expressions for all the measured quantities. It is concluded that the present model explains all features of the observations in a consistent way. Using only three adjustable parameters a good agreement exists also at a quantitative level. Experimental studies and theoretical modelling of the levitation force on a permanent magnet placed above a superconducting thin film are offered. It is shown that measurements of the levitation force is a simple and precise method to determine the critical current density in thin films

Impurity bound states in mesoscopic topological superconducting loops

Science.gov (United States)

Jin, Yan-Yan; Zha, Guo-Qiao; Zhou, Shi-Ping

2018-06-01

We study numerically the effect induced by magnetic impurities in topological s-wave superconducting loops with spin-orbit interaction based on spin-generalized Bogoliubov-de Gennes equations. In the case of a single magnetic impurity, it is found that the midgap bound states can cross the Fermi level at an appropriate impurity strength and the circulating spin current jumps at the crossing point. The evolution of the zero-energy mode can be effectively tuned by the located site of a single magnetic impurity. For the effect of many magnetic impurities, two independent midway or edge impurities cannot lead to the overlap of zero modes. The multiple zero-energy modes can be effectively realized by embedding a single Josephson junction with impurity scattering into the system, and the spin current displays oscillatory feature with increasing the layer thickness.

Majorana spin in magnetic atomic chain systems

Science.gov (United States)

Li, Jian; Jeon, Sangjun; Xie, Yonglong; Yazdani, Ali; Bernevig, B. Andrei

2018-03-01

In this paper, we establish that Majorana zero modes emerging from a topological band structure of a chain of magnetic atoms embedded in a superconductor can be distinguished from trivial localized zero energy states that may accidentally form in this system using spin-resolved measurements. To demonstrate this key Majorana diagnostics, we study the spin composition of magnetic impurity induced in-gap Shiba states in a superconductor using a hybrid model. By examining the spin and spectral densities in the context of the Bogoliubov-de Gennes (BdG) particle-hole symmetry, we derive a sum rule that relates the spin densities of localized Shiba states with those in the normal state without superconductivity. Extending our investigations to a ferromagnetic chain of magnetic impurities, we identify key features of the spin properties of the extended Shiba state bands, as well as those associated with a localized Majorana end mode when the effect of spin-orbit interaction is included. We then formulate a phenomenological theory for the measurement of the local spin densities with spin-polarized scanning tunneling microscopy (STM) techniques. By combining the calculated spin densities and the measurement theory, we show that spin-polarized STM measurements can reveal a sharp contrast in spin polarization between an accidental-zero-energy trivial Shiba state and a Majorana zero mode in a topological superconducting phase in atomic chains. We further confirm our results with numerical simulations that address generic parameter settings.

Effects of seed geometry on the crystal growth and the magnetic properties of single grain REBCO bulk superconductors

Energy Technology Data Exchange (ETDEWEB)

Lee, Hwi Joo; Lee, Hee Gyoun [Korea Polytechnic University, Siheung (Korea, Republic of); Park, Soon Dong; Jun, Bung Hyack; Kim, Chan Joong [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

2017-09-15

This study presents that the orientation and the geometry of seed affect on the growth behavior of melt processed single grain REBCO bulk superconductor and its magnetic properties. The effects of seed geometry have been investigated for thin 30mm x 30mm rectangular powder compacts. Single grain REBCO bulk superconductors have been grown successfully by a top seed melt growth method for 8-mm thick vertical thin REBCO slab. Asymmetric structures have been developed at the front surface and at the rear surface of the specimen. Higher magnetic properties have been obtained for the specimen that c-axis is normal to the specimen surface. The relationships between microstructure, grain growth and magnetic properties have been discussed.

Magnetically dead layers at sp-impurity-decorated grain boundaries and surfaces in nickel

Czech Academy of Sciences Publication Activity Database

Všianská, Monika; Šob, Mojmír

2011-01-01

Roč. 84, č. 1 (2011), Art.n. 014418 ISSN 1098-0121 R&D Projects: GA AV ČR IAA100100920; GA ČR GD106/09/H035 Institutional research plan: CEZ:AV0Z20410507 Keywords : magnetically dead layers * sp-impurity-decorated grain boundaries and surfaces * nickel Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.691, year: 2011

Possibilities of development photodynamic therapy under high temperature superconductor magnetic field

International Nuclear Information System (INIS)

Sen, Mihir

1996-01-01

After a long extensive research work neutron photon therapy for treatment of acquired immuno-deficiency syndrome (AIDS) was developed. High temperature superconductor magnet was developed and fitted in magnetic resonance imaging system to guide the patient. By this neutron-photon therapy AIDS effected cells are identified prominently. Patient is then injected with light sensitive drug molecules, which only AIDS cell retain. Light from photon (laser) then energizes the drug, which passes that energy to oxygen, which then leads a biochemical attack on the AIDS cells. If all goes well, the AIDS affected cells die. 10 refs., 1 fig

Development of superconductor application technology - Flywheel energy storage system using superconducting magnetic bearing

Energy Technology Data Exchange (ETDEWEB)

Lee, Soo Hun; Oh, Hueng Kuk; Yun, Keyng Reyl; Lee, Jeung Kun [Ahju University, Suwon (Korea, Republic of)

1996-06-01

Electricity must be used simultaneously with its generation. Existing storage methods either are dependent on special geography, are too expensive,= or are too inefficient. Electricity demand changes by as much as 30% over a 12-hour period and result in significant costs for utilities as power output get adjusted to meet these changes. The purpose of HTS FES is to store unused nighttime electricity until it is needed during the daytime. If every element of a rotating flywheel is stressed to a prescribed allowable value, the flywheel material will clearly be used in most efficient manner. The uniformlt stressed flywheel is about 25% stronger than a flat disk. The gap between superconductor and permanent magnet was 1.85 mm, and using bearing connector with the values, joining superconductor to permanent magnet Using bolt connector, joining permanent magnet to flywheel. Joined system is excited by exciting function that magnitude is 1, range is 0 up to 4000 HZ. 3 rd and 4 th natural frequency, 1857 HZ and 2340 HZ, in X direction and 2 nd natural frequency, 28.57 HZ, are avoided to prevent resonance. 15 refs., 11 tabs., 53 figs. (author)

Topological phase, electronic, magnetic and optical properties of ScPdBi compound with Gd, Np and Cm impurities

Energy Technology Data Exchange (ETDEWEB)

Narimani, Mitra; Nourbakhsh, Zahra, E-mail: z.nourbakhsh@sci.ui.ac.ir

2017-07-15

Highlights: • Gd, Np and Cm impurities induce the magnetic moment in ScPdBi compound. • ScPdBi compound with Gd, Np and Cm impurities has normal band order. • The ε(0) and R(0) increase by increasing the atomic number of X atom. - Abstract: The electronic, magnetic and optical properties of X-doped ScPdBi (X = Gd, Np, Cm) are investigated in the framework of density functional theory. The exchange-correlation potential is treated using generalized gradient approximation with Coulomb interaction parameter. The band order and energy band gap of X-doped ScPdBi are investigated by calculation of band structure. The effect of doping impurity on magnetic properties of ScPdBi compound is studied by calculation of total and partial magnetic moments of X-doped ScPdBi compound. Furthermore, the optical properties of X-doped ScPdBi are calculated and compared in the energy range of 0–25 eV.

Interaction of ultra soft magnetic materials with the high-T{sub c} superconductor YBCO

Energy Technology Data Exchange (ETDEWEB)

Stahl, Claudia; Treiber, Sebastian; Schuetz, Gisela [Max Planck Institute for Intelligent Systems, Heisenbergstrasse 3, 70569 Stuttgart (Germany); Walker, Patrick [Max Planck Institute for Intelligent Systems, Heisenbergstrasse 3, 70569 Stuttgart (Germany); Aalen University, Beethovenstrasse 1, 73430 Aalen (Germany); Albrecht, Joachim [Aalen University, Beethovenstrasse 1, 73430 Aalen (Germany)

2013-07-01

We have grown bilayers of optimally doped YBa{sub 2}Cu{sub 3}O{sub 7-δ} (YBCO) and ferromagnetic CoFeB on single-crystalline substrates by pulsed laser deposition and sputtering. These heterostructures are typically composed of about 100 nm YBCO and several 10 nm of CoFeB. Regarding the superconductor, the properties of the YBCO film change as a consequence of the vicinity of the ferromagnet. In detail we investigated the critical current density as a function of temperature, applied field and time as well as the transition temperature by SQUID magnetization measurements and quantitative magneto-optical measurements. The amorphous material CoFeB exhibits an in plane anisotropy and a very low coercivity. From magneto-optical images we find that the flux line lattice of the superconductor is mapped into the magnet and still visible as significant magnetic out-of-plane contrast at room temperature. We discuss this phenomenon as a new route to high-resolution mapping of the flux line distribution on a nanometer scale.

Development of high temperature superconductors for magnetic field applications

International Nuclear Information System (INIS)

Larbalestier, D.C.

1991-01-01

The key requirement for magnetic field applications of high temperature superconductor (HTS) materials is to have conductors with high transport critical current density available for magnet builders. After 3 or 4 years of being without any such object, conductor makers have had recent success in producing simple conductor prototypes. These have permitted the construction of simple HTS magnets having self fields exceeding 1 tesla at 4K. Thus the scientific feasibility of making powerful HTS magnets has been demonstrated. Attention to the technological aspects of making HTS conductors for magnets with strong flux pinning and reduced superconducting granularity is now sensible and attractive. However, extrinsic defects such as filament sausaging, cracking, misaligned grains and other perturbations to long range current flow must be controlled at a low level if the benefit of intrinsic improvements to the critical current density is to be maintained in the conductor form. Due to the great complexity of HTS materials, there is sometimes confusion as to whether a given sample has an intrinsically or extrinsically limited critical current density. Systematic microstructure variation experiments and resistive transition analysis are shown to be particularly helpful in this phase of conductor development

Spinning rate decay of levitated high-Tc superconductors in rotational magnetic field

Energy Technology Data Exchange (ETDEWEB)

Terentiev, A.N.; Kutukova, E.O.; Kuznetsov, A.A. (Inst. of Chemical Physics, Academy of Sciences, Moscow (Russia)); Mozhaev, A.P. (Moscow State Univ., Dept. of Chemistry (Russia))

1992-04-01

The rotation damping of a levitated superconductor was examined in the static field of a ring-shaped magnet and in the rotating field of coils. It was demonstrated that the pinning force mainly contributed to magnetic friction while the influence of a viscous component was negligible. The rotating magnetic field created a torque, reducing the angular deceleration under relaxation. Dependence of the rotational field-induced torque on the field-intensity was step-like. A relationship between the step-like behavior of rotational field-induced torque and pinning center distribution is discussed. The origins of friction torque and rotational field-produced torque are discussed. (orig.).

Superconductors with excess quasiparticles

International Nuclear Information System (INIS)

Elesin, V.F.; Kopaev, Y.V.

1981-01-01

This review presents a systematic kinetic theory of nonequilibrium phenomena in superconductors with excess quasiparticles created by electromagnetic or tunnel injection. The energy distributions of excess quasiparticles and of nonequilibrium phonons, dependence of the order parameter on the power and frequency (or intensity) of the electromagnetic field, magnetic properties of nonequilibrium superconductors, I-V curves of superconductor-insulator-superconductor junctions, and other properties are described in detail. The stability of superconducting states far from thermodynamic equilibrium is investigated and it is shown that characteristic instabilities leading to the formation of nonuniform states of a new type or phase transitions of the first kind are inherent to superconductors with excess quasiparticles. The results are compared with experimental data

Impurities in the heavy-fermion superconductor UBe13 (invited)

International Nuclear Information System (INIS)

Smith, J.L.; Fisk, Z.; Willis, J.O.; Batlogg, B.; Ott, H.R.

1984-01-01

Small amounts of Sc, Lu, Gd, Np, Ce, Th, La, and Ba have been substituted for uranium in UBe 13 to observe their effects on the superconducting and normal state properties. The thorium, which was the most complete study, resulted in an extremely unusual nonmonotonic depression of the transition temperature for a nonmagnetic impurity. This comes from an interplay that exists between the lowest temperature resistivity peak and the transition temperature, as the peak is depressed. These results suggest that heavy Fermion superconductivity is only one of the possible ground states for heavy mass electron systems. All of the impurities tested resulted in a transition temperature depression

Vibration measurements and analyses for a magnet-superconductor levitated system

International Nuclear Information System (INIS)

Wen Zheng; Liu Yu; Yang Wenjiang; Qiu Ming

2007-01-01

Magnetic levitation technology, having the characteristics of low cost and high quality, has been considered a preferable option for the next generation of launcher systems. A world-wide research design on the conceptual level has been carried out on the highly reusable space transportation systems by applying magnetic levitation to the launch assistance. Recently, a research plan has been implemented in our laboratory by constructing a scale-model suspension system with high temperature superconductor (HTS henceforth) bulks over a 7 m Nd-Fe-B permanent-magnet (PM henceforth) track for the launch assistance. An experimental platform was built to investigate the dynamic responses of the PM-HTS interaction at different field-cooled positions. The critical frequencies and amplitudes which lead to the instability of levitation drift were investigated. The stiffness and the vibration damping were also discussed at the zero-field-cooled position

Levitation performance of high-T{sub c} superconductor in sinusoidal guideway magnetic field

Energy Technology Data Exchange (ETDEWEB)

Liu, W. [Applied Superconductivity Laboratory, Southwest Jiaotong University, Chengdu 610031 (China)], E-mail: asclab@asclab.cn; Wang, J.S.; Jing, H.; Jiang, M.; Zheng, J.; Wang, S.Y. [Applied Superconductivity Laboratory, Southwest Jiaotong University, Chengdu 610031 (China)

2008-12-01

The vertical component of the Halbach array's magnetic field exhibits a sinusoid distribution because of the closed magnetic flux area between two neighbouring poles, so this field can be regarded as the sinusoidal magnetic field. This article mainly discusses the influence of the closed flux region on the levitation performance of the bulk high-temperature superconductor (HTS). Moreover, the levitation performance is compared between the closed and diverging region of magnetic flux. The experimental results can be analyzed by the magnetic circuit theory and the frozen-image model. The analysis indicates that the closed region of magnetic flux can influence the levitation performance of bulk HTS obviously and provide an extra useful guidance force. These conclusions are helpful to optimize the HTS Maglev system.

Magnetic behavior of light rare earth ions in (Nd,Eu,Gd)-123 superconductors

Czech Academy of Sciences Publication Activity Database

Jirsa, Miloš; Rameš, Michal; Marcenat, C.; Wolf, T.

2013-01-01

Roč. 26, č. 4 (2013), s. 901-905 ISSN 1557-1939 R&D Projects: GA MŠk(CZ) ME10069 Institutional support: RVO:68378271 Keywords : high- T c superconductors * cuprates * thermodynamic properties * LRE-123 * paramagnetic ions Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 0.930, year: 2013

Method and apparatus to trigger superconductors in current limiting devices

Science.gov (United States)

Yuan, Xing; Hazelton, Drew Willard; Walker, Michael Stephen

2004-10-26

A method and apparatus for magnetically triggering a superconductor in a superconducting fault current limiter to transition from a superconducting state to a resistive state. The triggering is achieved by employing current-carrying trigger coil or foil on either or both the inner diameter and outer diameter of a superconductor. The current-carrying coil or foil generates a magnetic field with sufficient strength and the superconductor is disposed within essentially uniform magnetic field region. For superconductor in a tubular-configured form, an additional magnetic field can be generated by placing current-carrying wire or foil inside the tube and along the center axial line.

Electromechanical properties of superconductors for DOE/OFE applications. Final report

International Nuclear Information System (INIS)

Ekin, J.W.; Bray, S.L.

1998-01-01

In many superconductor applications, especially large magnets, the superconductor is required to perform while under the influence of strong mechanical forces. These forces are commonly due to residual fabrication stress, differential thermal contraction of dissimilar materials, and electromagnetic forces generated within an energized magnet coil. Thorough knowledge of a superconductor's electrical performance under the influence of these forces (electromechanical properties) is required for successful magnet engineering. This report presents results of research conducted during the period from august 1993 through March 1997 on the electromechanical properties of superconductors for DOE/OFE fusion applications

Iron pnictide superconductors

International Nuclear Information System (INIS)

Tegel, Marcus Christian

2011-01-01

The scope of this dissertation therefore has not only been the synthesis of various new superconducting and non-superconducting iron pnictides of several structural families but also their in-depth crystallographic and physical characterisation. In Chapters 3 - 6, the family of the ZrCuSiAs-type (1111) compounds is subject of discussion. The solid solution series La(Co x Fe 1-x )PO is analysed regarding magnetic and superconducting properties and the new compounds EuMnPF and REZnPO, as well as the new superconductor parent compound SrFeAsF are presented. Chapters 7 - 9 are dedicated to the new iron arsenide superconductors of the ThCr 2 Si 2 -type (122 family). Therein, also the discovery of the first superconductor in this structural family, Ba 0.6 K 0.4 Fe 2 As 2 , is unveiled. A detailed examination of the complete solid solution series (Ba 1-x K x )Fe 2 As 2 is presented. Moreover, the crystallographic phase transitions of the closely related compounds SrFe 2 As 2 and EuFe 2 As 2 are characterised and the superconductors Sr 1-x K x Fe 2 As 2 and Ca 1-x Na x Fe 2 As 2 are examined for magnetic and phononic excitations. In Chapter 10, the redetermined crystal structure of the superconductor Fe(Se 1-x Te x ) (11-type) is presented from a chemist's point of view. Chapters 11 - 14 look into the superconducting and non-superconducting iron arsenides of more complex structural families (32522-type and 21311-type). Therein, crystallographic and magnetic details of Sr 3 Sc 2 O 5 Fe 2 As 2 are presented and Ba 2 ScO 3 FeAs and Sr 2 CrO 3 FeAs, the first two members of the new 21311-type are portrayed. Sr 2 CrO 3 FeAs is looked at in close detail with various methods, so e.g. the spin structure of the magnetically ordered compound is solved and a possible reason for the absence of superconductivity in this compound is given. Finally, the superconductor Sr 2 VO 3 FeAs is scrutinised and necessary prerequisites for superconductivity in this compound are suggested. (orig.)

Magnetic sheath effect on the gross and net erosion rates due to impurities

Science.gov (United States)

Mellet, N.; Pégourié, B.; Martin, C.; Gunn, J. P.; Bufferand, H.; Roubin, P.

2016-02-01

Simulations of impurity trajectories in deuterium plasmas in the vicinity of the surface are performed by taking into account the magnetic sheath in conditions relevant for ITER and WEST. We show that the magnetic sheath has a strong effect on the average impact angle of impurities in divertor conditions and that it can lead to an increase of ≈ 60% at the gross erosion maximum for neon (Ne+4) compared to the case when only the cyclotron motion is considered. The evaluation of the net erosion has been undertaken by retaining local redeposition of tungsten (W). We investigate how it is affected by the sheath magnetic potential profile. The largest effect is however observed when an energy distribution is considered. In this case the number of particles that manage to exit the sheath is larger as it is dominated by the more energetic particles. The comparison with other work is also discussed. The application to a scenario of the WEST project is finally performed, which exhibits a moderate, however non negligible, erosion of the plasma facing components.

Magnetic oscillations and quasiparticle band structure in the mixed state of type-II superconductors

International Nuclear Information System (INIS)

Norman, M.R.; MacDonald, A.H.; Akera, H.

1995-01-01

We consider magnetic oscillations due to Landau quantization in the mixed state of type-II superconductors. Our work is based on a previously developed formalism which allows the mean-field gap equations of the Abrikosov state to be conveniently solved in a Landau-level representation. We find that the quasiparticle band structure changes qualitatively when the pairing self-energy becomes comparable to the Landau-level separation. For small pairing self-energies, Landau-level mixing due to the superconducting order is weak and magnetic oscillations survive in the superconducting state although they are damped. We find that the width of the quasiparticle Landau levels in this regime varies approximately as Δ 0 n μ -1/4 where Δ 0 is proportional to the magnitude of the order parameter and n μ is the Landau-level index at the Fermi energy. For larger pairing self-energies, the lowest energy quasiparticle bands occur in pairs which are nearly equally spaced from each other and evolve with weakening magnetic field toward the bound states of an isolated vortex core. These bands have a weak magnetic field dependence and magnetic oscillations vanish rapidly in this regime. We discuss recent observations of the de Haas--van Alphen effect in the mixed state of several type-II superconductors in light of our results

A theoretical study of the influence of superconductor and magnet dimensions on the levitation force and stability of maglev systems

International Nuclear Information System (INIS)

Del-Valle, Nuria; Sanchez, Alvaro; Navau, Carles; Chen Duxing

2008-01-01

The levitation force and stability of superconducting levitation devices are strongly dependent on both the geometry and dimensions of the components and the cooling process of the superconductor. In this work we study these effects in levitating systems consisting of an infinitely long superconductor and a guideway of different arrangements of infinitely long parallel permanent magnets. Using a model based on the critical-state model and a magnetic-energy minimization procedure, taking into account the demagnetization fields, we analyze the influence of parameters of the system such as the width and height of the superconductor and those of the permanent magnets on the levitation force and stability for two different cooling processes, field cooling and zero-field cooling. The theoretical predictions are compared with existing experimental data. From the results obtained, we provide some general trends on how the dimensions of the components of maglev systems could be chosen to improve both the levitation force and the stability.

A theoretical study of the influence of superconductor and magnet dimensions on the levitation force and stability of maglev systems

Energy Technology Data Exchange (ETDEWEB)

Del-Valle, Nuria; Sanchez, Alvaro; Navau, Carles; Chen Duxing [Grup d' Electromagnetisme, Departament de Fisica, Universitat Autonoma Barcelona, 08193 Bellaterra (Barcelona), Catalonia (Spain)

2008-12-15

The levitation force and stability of superconducting levitation devices are strongly dependent on both the geometry and dimensions of the components and the cooling process of the superconductor. In this work we study these effects in levitating systems consisting of an infinitely long superconductor and a guideway of different arrangements of infinitely long parallel permanent magnets. Using a model based on the critical-state model and a magnetic-energy minimization procedure, taking into account the demagnetization fields, we analyze the influence of parameters of the system such as the width and height of the superconductor and those of the permanent magnets on the levitation force and stability for two different cooling processes, field cooling and zero-field cooling. The theoretical predictions are compared with existing experimental data. From the results obtained, we provide some general trends on how the dimensions of the components of maglev systems could be chosen to improve both the levitation force and the stability.

Coulomb Impurity Problem of Graphene in Strong Coupling Regime in Magnetic Fields.

Science.gov (United States)

Kim, S C; Yang, S-R Eric

2015-10-01

We investigate the Coulomb impurity problem of graphene in strong coupling limit in the presence of magnetic fields. When the strength of the Coulomb potential is sufficiently strong the electron of the lowest energy boundstate of the n = 0 Landau level may fall to the center of the potential. To prevent this spurious effect the Coulomb potential must be regularized. The scaling function for the inverse probability density of this state at the center of the impurity potential is computed in the strong coupling regime. The dependence of the computed scaling function on the regularization parameter changes significantly as the strong coupling regime is approached.

Flux flow and flux dynamics in high-Tc superconductors

International Nuclear Information System (INIS)

Bennett, L.H.; Turchinskaya, M.; Swartzendruber, L.J.; Roitburd, A.; Lundy, D.; Ritter, J.; Kaiser, D.L.

1991-01-01

Because high temperature superconductors, including BYCO and BSSCO, are type 2 superconductors with relatively low H(sub c 1) values and high H(sub c 2) values, they will be in a critical state for many of their applications. In the critical state, with the applied field between H(sub c 1) and H(sub c 2), flux lines have penetrated the material and can form a flux lattice and can be pinned by structural defects, chemical inhomogeneities, and impurities. A detailed knowledge of how flux penetrates the material and its behavior under the influence of applied fields and current flow, and the effect of material processing on these properties, is required in order to apply, and to improve the properties of these superconductors. When the applied field is changed rapidly, the time dependence of flux change can be divided into three regions, an initial region which occurs very rapidly, a second region in which the magnetization has a 1n(t) behavior, and a saturation region at very long times. A critical field is defined for depinning, H(sub c,p) as that field at which the hysteresis loop changes from irreversible to reversible. As a function of temperature, it is found that H(sub c,p) is well described by a power law with an exponent between 1.5 and 2.5. The behavior of H(sub c,p) for various materials and its relationship to flux flow and flux dynamics are discussed

Simulation and measurement of ferromagnetic impurities in non-magnetic aeroengine turbine disks using fluxgate magnetometers

OpenAIRE

Sebastian Hantscher; Ruixin Zhou; Albert Seidl; Johann Hinken; Christian Ziep

2015-01-01

In this paper, ferromagnetic impurities in paramagnetic aeroengine turbine disks are investigated. Because such inclusions represent a significant threat in aviation, a detailed analysis is required for impured turbine disks. For this purpose, sensitive fluxgate magnetometers are used. After a premagnetisation, this sensor is able to detect small ferromagnetic particles by recording the variation of the magnetic flux density while the disk rotates below the sensor head. This trajectory create...

Proposed Spontaneous Generation of Magnetic Fields by Curved Layers of a Chiral Superconductor

Science.gov (United States)

Kvorning, T.; Hansson, T. H.; Quelle, A.; Smith, C. Morais

2018-05-01

We demonstrate that two-dimensional chiral superconductors on curved surfaces spontaneously develop magnetic flux. This geometric Meissner effect provides an unequivocal signature of chiral superconductivity, which could be observed in layered materials under stress. We also employ the effect to explain some puzzling questions related to the location of zero-energy Majorana modes.

Neutron scattering observations on the magnetic phases of rareearth ternary superconductors

International Nuclear Information System (INIS)

Moncton, D.E.

1979-01-01

A number of ternary compounds become superconducting even though they contain a chemically ordered sublattice of magnetic rare-earth ions. Studies of the physical properties of these materials have revealed anomalies below T/sub c/ which have been attributed to magentic ordering transitions. Usng neutron spectrometers at the Brookhaven National Laboratory, a group of us has demonstrated that simple magnetic structures with long-range order do occur, and we have solved some of the magnetic structures of these superconductors. Specifically, we have found that in DyMo 6 S 8 and TbMo 6 S 8 an antiferromagnetic structure coexists with superconductivity. In two other compounds, ErRh 4 B 4 and HoMo 6 S 8 we have found that the development of ferromagnetism is responsible for the quenching of superconductivity. A study of the critical magnetic neutron scattering near the superconducting → ferromagnetic transitions shows the presence of fluctuations into a state with an oscillatory magnetization of wave length lambda = 100A

Growth and Structural, Magnetic, and Magnetooptical Properties of ZnO Films Doped with a Fe57 3 d Impurity

Science.gov (United States)

Mezdrogina, M. M.; Aglikov, A. S.; Semenov, V. G.; Kozhanova, Yu. V.; Nefedov, S. G.; Shelukhin, L. A.; Pavlov, V. V.

2018-03-01

ZnO films obtained by high-frequency magnetron sputtering and doped with a Fe57 metallic 3 d impurity by the diffusion method are studied. The type of local environment of Fe57 impurity atoms on varying the deposition parameters of ZnO films is determined by Mössbauer spectroscopy. It is established that the ground state of Fe57 impurity atoms corresponds to metallic iron in the magnetically ordered state and there is a small fraction of Fe57 atoms with a local environment corresponding to the complex oxide Fe3O4, having the magnetically ordered state; there is also a fraction of iron atoms in the paramagnetic state. The magnetic and magnetooptical parameters of the films were measured using magnetooptic Kerr effect. The spectral dependences of the polar magnetooptic Kerr effect in ZnO(Fe57) films are measured in a photon energy range of 1.5-4.5 eV and simulated by the effective-medium method. It is established that ZnO(Fe57) possess an easy-plane magnetic anisotropy with a magnetization lying in the film plane.

Damping and non-linearity of a levitating magnet in rotation above a superconductor

International Nuclear Information System (INIS)

Druge, J; Jean, C; Laurent, O; Méasson, M-A; Favero, I

2014-01-01

We study the dissipation of moving magnets in levitation above a superconductor. The rotation motion is analyzed using optical tracking techniques. It displays a remarkable regularity together with long damping time up to several hours. The magnetic contribution to the damping is investigated in detail by comparing 14 distinct magnetic configurations and points towards amplitude-dependent dissipation mechanisms. The non-linear dynamics of the mechanical rotation motion is also revealed and described with an effective Duffing model. The magnetic mechanical damping is consistent with measured hysteretic cycles M(H) that are discussed within a modified critical state model. The obtained picture of the coupling of levitating magnets to their environment sheds light on their potential as ultra-low dissipation mechanical oscillators for high precision physics. (paper)

Trapped field recovery of bulk superconductor magnets by static field magnetization

Science.gov (United States)

Deng, Z.; Tsuzuki, K.; Miki, M.; Felder, B.; Hara, S.; Izumi, M.

2011-11-01

Thanks to the trapped field of bulk high-temperature superconductors, they can be used as field-pole magnets in the high temperature superconducting (HTS) rotating machines. For example, an output power of 10 kW at 720 rpm was realized by an average trapped field of 0.56 T of eight melt-textured GdBa2Cu3Oy (Gd-123) bulks at liquid nitrogen temperature in TUMSAT in 2004. Similarly to the HTS machines involving 1G or 2G wires, the trapped field of the bulk is possibly sensitive and even can be attenuated by the AC component field during the operation. Hence, it is necessary to recover the trapped field once being decreased to some extent in the practical application. From this point, we have investigated the trapped field recovery of HTS bulk magnets by static field magnetization in the paper. A series of different initial trapped fields after zero-field-cooling or field-cooling magnetization are used to simulate the attenuated trapped field. By comparing the trapped field peak and its distribution, the trapped field was found to be able to recover by the static field magnetization method with a stronger excitation field and the initial trapped flux inside the bulk also has an influence on the recovery process. The optimum recovery field was found to be about 2.5 times the saturated trapped field of the bulk at liquid nitrogen temperature, by which the bulk can regain the former best trapped field performance.

Donor impurity in nanotube with two GaAs/GaAlAs quantum wells: Magnetic field effects

Energy Technology Data Exchange (ETDEWEB)

Gonzalez, J D; Escorcia, R; Sierra-Ortega, J, E-mail: jdavid0831@gmail.co [Grupo de Investigacion en teorIa de la Materia Condensada, Universidad del Magdalena, A.A. 731, Santa Marta (Colombia)

2009-05-01

Micro-tubes containing two GaAs/GaAlAs quantum wells (QWs) in a section of the tube layer has been fabricated and optical properties of the embedded QWs has been studied. The ground state binding energy of an off-axis donor in a cylindrical nanotube, containing two GaAs/GaAlAs quantum wells (QWs) in the presence of a uniform magnetic field is calculated as a function of the donor location as well as the density of states. A trial function for describing the asymmetric electron charge distribution is taken as a product of the combination of 1s and 2p{sub x,y} subband wave functions and an unknown function that depends only on electron-ion separation. We found that the increasing the magnetic field the increasing the binding energy while the impurity is located in the QW1, whereas the opposite occurs when the impurity is located in the QW2. Two peaks in the curves of the binding energy, as a function of the impurity position, are also found as well as in the density of impurity states.

Magnetic field and force analysis of high Tc superconductor with flux flow and creep

International Nuclear Information System (INIS)

Yoshida, Yoshikatsu; Uesaka, Mitsuru; Miya, Kenzo

1994-01-01

This paper describes a new method for the magnetic force analysis of high T c superconductor based on the flux flow and creep model. The introduction of the artificial conductivity, which is used in the conventional method, is not needed. The CPU time requirement of the calculations is considerably lower than that in the case of the conventional method. Thereby the vibration of a levitated permanent magnet was numerically analyzed by taking into account the flux flow and creep

Measuring condensate fraction in superconductors

International Nuclear Information System (INIS)

Chakravarty, Sudip; Kee, Hae-Young

2000-01-01

An analysis of off-diagonal long-range order in superconductors shows that the spin-spin correlation function is significantly influenced by the order if the order parameter is anisotropic on a microscopic scale. Thus, magnetic neutron scattering can provide a direct measurement of the condensate fraction of a superconductor. It is also argued that recent measurements in high-temperature superconductors come very close to achieving this goal. (c) 2000 The American Physical Society

Scanning X-ray microscopy of superconductor/ferromagnet bilayers

Energy Technology Data Exchange (ETDEWEB)

Stahl, Claudia; Ruoss, Stephen; Weigand, Markus; Schuetz, Gisela [Max Planck Institute for Intelligent Systems, Stuttgart (Germany); Zahn, Patrick; Bayer, Jonas [Max Planck Institute for Intelligent Systems, Stuttgart (Germany); Research Institute for Innovative Surfaces, FINO, Aalen University (Germany); Albrecht, Joachim [Research Institute for Innovative Surfaces, FINO, Aalen University (Germany)

2016-07-01

The magnetic flux distribution arising from a high-T{sub c} superconductor is detected and visualized with high spatial resolution using scanning x-ray microscopy (SXM). Therefore, we introduce a sensor layer, namely, an amorphous, soft-magnetic CoFeB cover layer. The magnetic stray fields of the supercurrents lead to a local reorientation of the magnetic moments in the ferromagnet, which is visualized using the large x-ray magnetic circular dichroism (XMCD) effect of the Co and Fe L3-edge. We show that the XMCD contrast in the sensor layer corresponds to the in-plane magnetic flux distribution of the superconductor and can hence be used to image magnetic structures in superconductors with high spatial resolution. Using the total electron yield (TEY) mode the surface structure and the magnetic domains can be imaged simultaneously and can be correlated. The measurements are carried out at our scanning x-ray microscope MAXYMUS at Bessy II, Berlin with the new low temperature setup.

Effects of Exponential Nonlinear Electrodynamics and External Magnetic Field on Holographic Superconductors

Science.gov (United States)

Sheykhi, A.; Abdollahzadeh, Z.

2018-03-01

We investigate the effects of an external magnetic field as well as exponential nonlinear electrodynamics on the properties of s-wave holographic superconductors. Our strategy for this study is the matching method, which is based on the match of the solutions near the horizon and on the boundary at some intermediate point. When the magnetic field is turned off, we obtain the critical temperature as well as the condensation operator and show that the critical exponent is still 1/2, which is the universal value in the mean field theory. Then, we turn on the magnetic field and obtain the critical magnetic field, B c , in order to study its behavior in terms of the temperature. Interestingly enough, we find that in the presence of exponential nonlinear electrodynamics, the critical temperature decreases, while the critical magnetic field increases compared to the Maxwell case. We also observe that the critical magnetic field increases with increasing the nonlinear parameter b.

Trapped field recovery of bulk superconductor magnets by static field magnetization

Energy Technology Data Exchange (ETDEWEB)

Deng, Z., E-mail: zigang@kaiyodai.ac.jp [Laboratory of Applied Physics, Department of Marine Electronics and Mechanical Engineering, Tokyo University of Marine Science and Technology, Tokyo 135-8533 (Japan); Tsuzuki, K.; Miki, M.; Felder, B.; Hara, S.; Izumi, M. [Laboratory of Applied Physics, Department of Marine Electronics and Mechanical Engineering, Tokyo University of Marine Science and Technology, Tokyo 135-8533 (Japan)

2011-11-15

A series of initial trapped fields after ZFC or FC magnetization are used to simulate the attenuated trapped field. It is possible and easy to recover the lost trapped field and regain the best trapped field performance as before. In the re-magnetization process, the initial magnetic flux inside the bulk magnets will help to recover the trapped field. The optimum recovery field is recommended to be 2.5 times the saturation field of the bulk at LN2 temperature. Thanks to the trapped field of bulk high-temperature superconductors, they can be used as field-pole magnets in the high temperature superconducting (HTS) rotating machines. For example, an output power of 10 kW at 720 rpm was realized by an average trapped field of 0.56 T of eight melt-textured GdBa{sub 2}Cu{sub 3}O{sub y} (Gd-123) bulks at liquid nitrogen temperature in TUMSAT in 2004. Similarly to the HTS machines involving 1G or 2G wires, the trapped field of the bulk is possibly sensitive and even can be attenuated by the AC component field during the operation. Hence, it is necessary to recover the trapped field once being decreased to some extent in the practical application. From this point, we have investigated the trapped field recovery of HTS bulk magnets by static field magnetization in the paper. A series of different initial trapped fields after zero-field-cooling or field-cooling magnetization are used to simulate the attenuated trapped field. By comparing the trapped field peak and its distribution, the trapped field was found to be able to recover by the static field magnetization method with a stronger excitation field and the initial trapped flux inside the bulk also has an influence on the recovery process. The optimum recovery field was found to be about 2.5 times the saturated trapped field of the bulk at liquid nitrogen temperature, by which the bulk can regain the former best trapped field performance.

Spin power and efficiency in an Aharnov-Bohm ring with an embedded magnetic impurity quantum dot

Energy Technology Data Exchange (ETDEWEB)

Yang, Xi; Guo, Yong, E-mail: guoy66@tsinghua.edu.cn [Department of Physics and State Key Laboratory of Low-Dimensional Quantum Physics, Tsinghua University, Beijing 100084 (China); Collaborative Innovation Center of Quantum Matter, Beijing (China); Zheng, Jun [College of New Energy, Bohai University, Jinzhou 121013 (China); Chi, Feng [School of Physical Science and Technology, Inner Mongolia University, Huhehaote 010023 (China)

2015-05-11

Spin thermoelectric effects in an Aharnov-Bohm ring with a magnetic impurity quantum dot (QD) are theoretically investigated by using the nonequilibrium Green's function method. It is found that due to the exchange coupling between the impurity and the electrons in QD, spin output power, and efficiency can be significant and be further modulated by the gate voltage. The spin thermoelectric effect can be modulated effectively by adjusting the Rashba spin-orbit interaction (RSOI) and the magnetic flux. The spin power and efficiency show zigzag oscillations, and thus spin thermoelectric effect can be switched by adjusting the magnetic flux phase factor and RSOI ones. In addition, the spin efficiency can be significantly enhanced by the coexistence of the RSOI and the magnetic flux, and the maximal value of normalized spin efficiency η{sub max}/η{sub C} = 0.35 is obtained. Our results show that such a QD ring device may be used as a manipulative spin thermoelectric generator.

Flux pinning and critical current in layered type-II superconductors in parallel magnetic fields

International Nuclear Information System (INIS)

Prokic, V.; Davidovic, D.; Dobrosavljevic-Grujic, L.

1995-01-01

We have shown, within the Ginzburg-Landau theory, that the interaction between vortices and normal-metal layers in high-T c superconductor--normal-metal superlattices can cause high critical-current densities j c . The interaction is primarily magnetic, except at very low temperatures T, where the core interaction is dominant. For a lattice of vortices commensurate with an array of normal-metal layers in a parallel magnetic field H, strong magnetic pinning is obtained, with a nonmonotonic critical-current dependence on H, and with j c of the order of 10 7 --10 8 A/cm 2

Magnetic field modulated microwave spectroscopy across phase transitions and the search for new superconductors

International Nuclear Information System (INIS)

Ramírez, Juan Gabriel; Basaran, Ali C; De la Venta, J; Pereiro, Juan; Schuller, Ivan K

2014-01-01

This article introduces magnetic field modulated microwave spectroscopy (MFMMS) as a unique and high-sensitivity technique for use in the search for new superconductors. MFMMS measures reflected microwave power as a function of temperature. The modulation induced by the external ac magnetic field enables the use of phase locked detection with the consequent sensitivity enhancement. The MFMMS signal across several prototypical structural, magnetic, and electronic transitions is investigated. A literature review on microwave absorption across superconducting transitions is included. We show that MFMMS can be used to detect superconducting transitions selectively with very high sensitivity. (report on progress)

FY 1998 report on the results of the research and development of fundamental technologies for superconductor applications; 1998 nendo chodendo oyo kiban gijutsu kenkyukaihatsu seika hokokusho. Chodendo oyo kiban gijutsu keknyu kaihatsu

Energy Technology Data Exchange (ETDEWEB)

NONE

1999-05-01

As to the research on the superconductor manifestation mechanism, Y123 monocrystal which was partially replaced with Zn and Ni was manufactured, and it was made clear that the addition of these impurities greatly change anisotropy of superconductors. It was made clear that instability of lattice and magnetism is included in high temperature superconductor. Also made clear was an important role in the Nb/Ba replacement in existence of magnetic flux melting phase transfer and the magnetic field induced pinning effect. The manufacture of Y123 bicrystal membrane was successful by the liquid phase epitaxy method. The manufacture of non-copper base K-Bi-O new superconductor was successful by the ultra-high pressure synthesis method. The stabilized process was established for large size crystals of 15-20mm square in Y base and of 20-25mm square in Nd base. Also successful was the growth by LPE method of crystal with thick membrane of 20mm x 20mm x 10{mu}m on the MgO monocrystal substrate. The non-bicrystalization of Y base Nd base monocrystal was successful, and the peak phenomenon control in Jc-H was found out. By neutron irradiation, the acquisition magnetic field of 3.7T at 77K was achieved using bulk Y base 123 material with diameter of 3cm. And, the critical current density of 60,000 A/cm{sup 2} was achieved at 77K and 3T. (NEDO)

Magnetic hysteresis and complex susceptibility as measures of ac losses in a multifilamentary NbTi superconductor

International Nuclear Information System (INIS)

Goldfarb, R.B.; Clark, A.F.

1985-01-01

Magnetization and ac susceptibility of a standard NbTi superconductor were measured as a function of longitudinal dc magnetic field. The ac-field-amplitude and frequency dependences of the complex susceptibility are examined. The magnetization is related to the susceptibility by means of a theoretical derivation based on the field dependence of the critical current density. Hysteresis losses, obtained directly from dc hysteresis loops and derived theoretically from ac susceptibility and critical current density, were in reasonable agreement

Magnetism and superconductivity in a heavy-fermion superconductor, CePt3Si

International Nuclear Information System (INIS)

Takeuchi, T; Hashimoto, S; Yasuda, T; Shishido, H; Ueda, T; Yamada, M; Obiraki, Y; Shiimoto, M; Kohara, H; Yamamoto, T; Sugiyama, K; Kindo, K; Matsuda, T D; Haga, Y; Aoki, Y; Sato, H; Settai, R; Onuki, Y

2004-01-01

We have studied the magnetic and thermal properties of a single crystal of CePt 3 Si, which is a recently reported heavy-fermion superconductor with a superconducting transition temperature T c = 0.75 K and a Neel temperature T N = 2.2 K. The overall experimental data are principally explained on the basis of the crystalline electric field (CEF) scheme. Even in the antiferromagnetic state, the CEF model applies well to the characteristic features in the magnetization curve. These results indicate the existence of a localized magnetic moment at the Ce site, with a considerably reduced ordered moment of 0.16 μ B /Ce, and the strongly correlated conduction electrons are condensed into the superconducting state. We have also constructed the magnetic phase diagram including the superconducting phase for H parallel [110] and [001]. (letter to the editor)

Cooling achieved by rotating an anisotropic superconductor in a constant magnetic field: A new perspective

Directory of Open Access Journals (Sweden)

Manh-Huong Phan

2016-12-01

Full Text Available A new type of rotary coolers based on the temperature change (ΔTrot of an anisotropic superconductor when rotated in a constant magnetic field is proposed. We show that at low temperature the Sommerfeld coefficient γ(B,Θ of a single crystalline superconductor, such as MgB2 and NbS2, sensitively depends on the applied magnetic field (B and the orientation of the crystal axis (Θ, which is related to the electronic entropy (SE and temperature (T via the expression: SE=γT. A simple rotation of the crystal from one axis to one another in a constant magnetic field results in a change in γ and hence SE: ΔSE=ΔγT. A temperature change −ΔTrot ∼ 0.94 K from a bath temperature of 2.5 K is achieved by simply rotating the single crystal MgB2 by 90° with respect to the c-axis direction in a fixed field of 2 T. ΔTrot can be tuned by adjusting the strength of B within a wide magnetic field range. Our study paves the way for development of new materials and cryogenic refrigerators that are potentially more energy-efficient, simplified, and compact.

Influence of iron impurities on defected graphene

Energy Technology Data Exchange (ETDEWEB)

Faccio, Ricardo; Pardo, Helena [Centro NanoMat, Cryssmat-Lab, DETEMA, Polo Tecnológico de Pando, Facultad de Química, Universidad de la República, Cno. Saravia s/n, CP 91000 Pando (Uruguay); Centro Interdisciplinario en Nanotecnología, Química y Física de Materiales, Espacio Interdisciplinario, Universidad de la República, Montevideo (Uruguay); Araújo-Moreira, Fernando M. [Materials and Devices Group, Department of Physics, Universidade Federal de São Carlos, SP 13565-905 (Brazil); Mombrú, Alvaro W., E-mail: amombru@fq.edu.uy [Centro NanoMat, Cryssmat-Lab, DETEMA, Polo Tecnológico de Pando, Facultad de Química, Universidad de la República, Cno. Saravia s/n, CP 91000 Pando (Uruguay); Centro Interdisciplinario en Nanotecnología, Química y Física de Materiales, Espacio Interdisciplinario, Universidad de la República, Montevideo (Uruguay)

2015-03-01

Highlights: • The interaction among a multivacancy graphene system and iron impurities is studied. • The studied iron impurities were single atom and tetrahedral and octahedral clusters. • DFT calculations using the VASP code were performed. • The embedding of Fe affects the structure and electronic behavior in the graphene. • Half metal or semimetal behavior can be obtained, depending on the Fe impurities. - Abstract: The aim of this work is to study the interaction of selected iron cluster impurities and a multivacancy graphene system, in terms of the structural distortion that the impurities cause as well as their magnetic response. While originally, the interaction has been limited to vacancies and isolated metallic atoms, in this case, we consider small iron clusters. This study was undertaken using Density Functional Theory (DFT) calculations. The influence of the iron impurities in the electronic structure of the vacant graphene system is discussed. The main conclusion of this work is that the presence of iron impurities acts lowering the magnetic signal due to the occurrence of spin pairing between carbon and iron, instead of enhancing the possible intrinsic carbon magnetism.

Influence of iron impurities on defected graphene

International Nuclear Information System (INIS)

Faccio, Ricardo; Pardo, Helena; Araújo-Moreira, Fernando M.; Mombrú, Alvaro W.

2015-01-01

Highlights: • The interaction among a multivacancy graphene system and iron impurities is studied. • The studied iron impurities were single atom and tetrahedral and octahedral clusters. • DFT calculations using the VASP code were performed. • The embedding of Fe affects the structure and electronic behavior in the graphene. • Half metal or semimetal behavior can be obtained, depending on the Fe impurities. - Abstract: The aim of this work is to study the interaction of selected iron cluster impurities and a multivacancy graphene system, in terms of the structural distortion that the impurities cause as well as their magnetic response. While originally, the interaction has been limited to vacancies and isolated metallic atoms, in this case, we consider small iron clusters. This study was undertaken using Density Functional Theory (DFT) calculations. The influence of the iron impurities in the electronic structure of the vacant graphene system is discussed. The main conclusion of this work is that the presence of iron impurities acts lowering the magnetic signal due to the occurrence of spin pairing between carbon and iron, instead of enhancing the possible intrinsic carbon magnetism

Neutron Depolarization in Superconductors

Science.gov (United States)

Zhuchenko, N. K.

1995-04-01

The dependences of neutron depolarization on applied magnetic field are deduced along the magnetization hysteresis loop in terms of the Bean model of the critical state. The depolarization in uniaxial superconductors with the reversible magnetization, including uniaxial magnetic superconductors, is also considered. A strong depolarization is expected if the neutrons travel along the vortex lines. On calcule la dépendance en champ magnétique de la dépolarisation des neutrons le long du cycle d'hystérésis en termes du modèle critique de Bean. On considère aussi la dépolarisation dans les supraconducteurs uniaxiaux en fonction de l'aimantation réversible, y compris pour les supraconducteurs magnétiques. On attend une forte dépolarisation si les neutrons se propagent le long des vortex.

Levitation force and magnetization in bulk and thin film high T{sub c} superconductors

Energy Technology Data Exchange (ETDEWEB)

Riise, A.B

1998-04-01

The authors present high-resolution measurements of the repulsive vertical force and its associated stiffness between a Nd-B-Fe magnet and a YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} superconductor in cylindrical geometry. The results are compared with theoretical predictions. The calculations are based on a model in which the superconductor is assumed to be either a sintered granular material or consisting of grains embedded in a nonactive matrix so that only intragranular currents are important. The critical state model is applied to each grain individually and closed form expressions for both vertical force F{sub z} and stiffness are obtained in a configuration with cylindrical symmetry. The model explains all features of the experimental results in a consistent way. A good quantitative agreement has been obtained using only three adjustable parameters. Several central aspects of the phenomenon of magnetic levitation with high-T{sub c} superconductors are presented. High-resolution measurements are made of the repulsive vertical force and its associated stiffness as well as the horizontal stabilizing force and the stiffness governing lateral vibrations. The results obtained at 77 K using a granular YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} sample and Nd-Fe-B magnet in a rectangular levitation configuration are compared with theoretical predictions. The calculations, which are based on the critical state model with the assumption that it applies to the grins individually, give closed-form expressions for all the measured quantities. It is concluded that the present model explains all features of the observations in a consistent way. Using only three adjustable parameters a good agreement exists also at a quantitative level. Experimental studies and theoretical modelling of the levitation force on a permanent magnet placed above a superconducting thin film are offered. It is shown that measurements of the levitation force is a simple and precise method to determine the

Collective impurity effects in the Heisenberg triangular antiferromagnet

International Nuclear Information System (INIS)

Maryasin, V S; Zhitomirsky, M E

2015-01-01

We theoretically investigate the Heisenberg antiferromagnet on a triangular lattice doped with nonmagnetic impurities. Two nontrivial effects resulting from collective impurity behavior are predicted. The first one is related to presence of uncompensated magnetic moments localized near vacancies as revealed by the low-temperature Curie tail in the magnetic susceptibility. These moments exhibit an anomalous growth with the impurity concentration, which we attribute to the clustering mechanism. In an external magnetic field, impurities lead to an even more peculiar phenomenon lifting the classical ground-state degeneracy in favor of the conical state. We analytically demonstrate that vacancies spontaneously generate a positive biquadratic exchange, which is responsible for the above degeneracy lifting

Small magnetic energy storage systems using high temperature superconductors

International Nuclear Information System (INIS)

Kumar, B.

1991-01-01

This paper reports on magnetic energy storage for power systems that has been considered for commercial utility power, air and ground mobile power sources, and spacecraft applications. Even at the current technology limits of energy storage (100 KJ/Kg*), superconducting magnetic energy storage inductors do not offer a strong advantage over state-of-the-art batteries. The commercial utility application does not have a weight and volume limitation, and is under intense study in several countries for diurnal cycle energy storage and high power delivery. The advent of high temperature superconductors has reduced one of the penalties of superconducting magnetic energy storage in that refrigeration and cryocontainers become greatly simplified. Still, structural and current density issues that limit the energy density and size of superconducting inductors do not change. Cold weather starting of aircraft engines is an application where these limitations are not as significant, and where current systems lack performance. The very cold environments make it difficult to achieve high power densities in state-of-the-art batteries and hydraulically activated starters. The same cold environments make it possible to cool superconducting systems for weeks using a single charge of liquid nitrogen. At the same, the ground carts can handle the size and weight of superconducting magnetic storage (SMES) devices

Pinning and creep in high-Tc superconductors

International Nuclear Information System (INIS)

Ovchinnikov, Yu.N.; Ivlev, B.I.

1992-01-01

The angular and magnetic field dependence of a critical current parallel to the layers in the layered superconductors is studied. The critical current value is found for a superconductor with strong pinning centers. Quantum flux creep in sufficiently perfect layered high-Tc superconductors is discussed. The cross-over temperature between activated and quantum creep is found. (orig.)

GGA+U investigations of impurity d-electrons effects on the electronic and magnetic properties of ZnO

KAUST Repository

Ul Haq, Bakhtiar

2014-08-01

Stimulation of novel features in ZnO by impurity electrons has attracted a remarkable attention of researchers from the past decade. Consequently, ZnO has found several applications in the field of spintronics and optoelectronics. We report, the effect of 3d-(V, Ag) electrons on the properties of ZnO in stable wurtzite (WZ) and metastable zincblende (ZB) phase using the density functional theory. Introduction of V-3d electrons was found to induce a high magnetic moment value of 5.22 in WZ and 3.26 in the ZB phase, and moreover transform the semiconductor character of ZnO into a metallic nature. Ag-d electrons result in the p-type half-metallic nature of ZnO with a weak ferromagnetic background. Our calculations for ground-state magnetic ordering show that ZnO in the presence of impure 3d-(V, Ag) electrons favors ferromagnetic ordering, and obey the double exchange mechanism. However, impurity atoms have very marginal effect on the lattice parameters of ZnO, thereby exposing its potential to absorb the impurity atoms in high concentration. © 2014 Elsevier B.V. All rights reserved.

Influence of Magnetic Ordering between Cr Adatoms on the Yu-Shiba-Rusinov States of the β -Bi2Pd Superconductor

Science.gov (United States)

Choi, Deung-Jang; Fernández, Carlos García; Herrera, Edwin; Rubio-Verdú, Carmen; Ugeda, Miguel M.; Guillamón, Isabel; Suderow, Hermann; Pascual, José Ignacio; Lorente, Nicolás

2018-04-01

We show that the magnetic ordering of coupled atomic dimers on a superconductor is revealed by their intragap spectral features. Chromium atoms on the superconductor β -Bi2Pd surface display Yu-Shiba-Rusinov bound states, detected as pairs of intragap excitations in tunneling spectra. By means of atomic manipulation with a scanning tunneling microscope's tip, we form Cr dimers with different arrangements and find that their intragap features appear either shifted or split with respect to single atoms. These spectral variations are associated with the magnetic coupling, ferromagnetic or antiferromagnetic, of the dimer, as confirmed by density functional theory simulations. The striking qualitative differences between the observed tunneling spectra prove that intragap Shiba states are extremely sensitive to the magnetic ordering on the atomic scale.

The Superconductors that Magnets Really Want: What Stands in the Way? (Superconductors for Accelerator Use: What Next and How Close is the Ideal Conductor?)

International Nuclear Information System (INIS)

Larbalestier, David

2009-01-01

There are over 5000 superconducting materials but only about 5 have ever been useful for applications in magnets, while HEP, which has been so vital for the development of superconducting magnet technology has made virtually every magnet out of just one, the simple bcc alloy Nb-Ti with Tc of 9 K and upper critical field ∼ 14T (at 2K). Significant demonstrations of the capability of the brittle intermetallic Nb3Sn have shown that fields of more than 15 T can be generated in dipole form. But Nb-Ti and Nb3Sn are staid, conventional superconductors, far from the cutting edge of superconducting science research where cuprates like YBa2Cu3O7-x and Bi2Sr2CaCu2Ox remain at the scientific forefront and in 2008 were joined by the recently discovered Fe-As pnictide superconductors. What could it mean to have materials for magnets with 10 times the Tc of Nb-Ti (90-120 K) and 3 or more times the critical field (100-240 T)? One enormous barrier is that higher Tc so far always means more complexity and a more localized superconducting interaction which is sensitive to local loss of superconductivity. The issue that has made the cuprate high temperature superconductors so hard to apply is that grain boundaries which form a 3D network in any practical wire form, easily acquire degraded superconducting properties. But conductors can now be made with extreme texture so that grain boundaries are minimized. Moreover almost practical conductors of Bi2Sr2CaCu2Ox and YBa2Cu3O7-x are now are in production and in late 2008 we were, at the Magnet Lab, able to make small solenoids operating at high current density in fields of 32 and almost 34 T respectively. Within the HEP community, there is enthusiasm to embrace HTS conductors for new very high field machines that could, like the Muon Collider, use fields of 30-50 T. In my talk I would like to explore the underlying science controlling such potential applications.

Ceramic high temperature superconductor levitating motor with laser commutator

International Nuclear Information System (INIS)

Roslan Abd Shukor; Lee Keng Heong

1996-01-01

The design of a magnetically levitating motor using a ceramic high temperature superconductor with laser commutator is discussed. A YBa sub 2 Cu sub 3 O sub 7-δ high temperature superconductor with 25 mm diameter and 6 mm thickness is used to levitate a Nd-Fe-B magnet (19.0 mm diameter and 4.8 mm thickness) which is attached symmetrically to a 150 mm long graphite rod. A smaller magnet (5.5 mm diameter and 2.0 mm thickness) is attached at each end of the rod with the appropriate poles arrangements. A suitable laser beam chopper is used to optically drive a solenoid which repels the smaller magnets thus driving the motor. A simple and efficient liquid nitrogen supply system is designed to cool the superconductor. The stability of the bearing is provided by the flux pinning in this type-II superconductor. Some characteristics of the motor are discussed

Reversible and irreversible magnetization of the Chevrel-phase superconductor PbMo6S8

International Nuclear Information System (INIS)

Zheng, D.N.; Ramsbottom, H.D.; Hampshire, D.P.

1995-01-01

Magnetic measurements have been carried out on the hot-isostatically-pressed Chevrel-phase superconductor PbMo 6 S 8 at temperatures from 4.2 K to T c and for magnetic fields up to 12 T. The results show that for the PbMo 6 S 8 compound there is a wide magnetically reversible region, between the irreversibility field B irr and the upper critical field B c2 , on the isothermal magnetic hysteresis curves. The B irr (T) line, i.e., the irreversibility line, was found to obey a power-law expression: B irr =B * (1-T/T c ) α with α∼1.5. Magnetic relaxation measurements revealed that the flux-creep effect in the material studied is substantial and is greater than those observed in conventional metallic alloys, but smaller than in high-temperature superconductors. The existence of the irreversibility line and pronounced flux-creep effect in PbMo 6 S 8 is attributed to the short coherence length of the material. From the reversible magnetization data, the values of the penetration depth, the coherence length, and the critical fields are obtained together with the Ginzburg-Landau parameter κ. At 4.2 K, the critical current density J c is 10 9 A m -2 at zero field, and decreases to 2x10 8 A m -2 at 10 T. Pinning force curves measured at different temperatures obey a Kramer-scaling law of the form: F p (=J c xB)∝b 1/2 (1-b) 2 , which indicates that the J c is limited by one predominant flux-pinning mechanism

Rigid levitation, flux pinning, thermal depinning, and fluctuation in high-Tc superconductors

International Nuclear Information System (INIS)

Brandt, E.H.

1991-01-01

Here, the author shows that the strong velocity-independent frictional force on a levitating superconductor and on any type-II superconductor moving in a homogeneous magnetic field is caused by pinning and depinning of the magnetic flux lines in its interior. Levitation may thus be used to investigate the pinning properties of a superconductor, and friction in a superconductor bearing may be minimized by choosing appropriate materials and geometries

Boron, nitrogen, and nickel impurities in GeC nanoribbons: A first-principles investigation

Energy Technology Data Exchange (ETDEWEB)

Xu, Zhuo; Li, Yangping, E-mail: liyp@nwpu.edu.cn; Liu, Zhengtang

2017-07-01

Highlights: • The impurities preferentially substitutes the Ge atom at the ribbon edge. • The impurities could result in a reduction of the band gap of 7-AGeCNR. • The impurities turns the metallic behavior of 4-ZGeCNR into semiconductor. • The impurities could change the magnetic moment of 4-ZGeCNR. • The impurities could introduce magnetic moments into the non-magnetic 7-AGeCNR. - Abstract: Using first-principles calculations based on the density functional theory we investigated the structural, electronic and magnetic properties of substitutional boron, nitrogen, and nickel impurities in germanium carbide (GeC) nanoribbons. Hydrogen terminated GeC ribbons with armchair and zigzag edges are considered here. We observed that all three impurities preferentially substitutes the Ge atom at the ribbon edge. In addition, the electronic band structures of the doped systems indicate that (i) the impurities could introduce impurity bands in the band gap and resulting in a reduction of the band gap of 7-AGeCNR, (ii) the metallic behavior of 4-ZGeCNR turns into semiconductor because of the incorporation of the impurities, (iii) the impurities could change the magnetic moment of 4-ZGeCNR and even introduce magnetic moment into the non-magnetic 7-AGeCNR.

Influence of lateral displacement on the levitation performance of a magnetized bulk high-Tc superconductor magnet

International Nuclear Information System (INIS)

Liu, W.; Wang, J.S.; Ma, G.T.; Zheng, J.; Tuo, X.G.; Li, L.L.; Ye, C.Q.; Liao, X.L.; Wang, S.Y.

2012-01-01

Compared with the permanent magnet, the magnetized bulk high-T c superconductor magnet (MBSCM) can trap higher magnetic field due to its strong flux pinning ability, so it is a good candidate to improve the levitation performance of high-T c superconductive (HTS) maglev system. The trapped magnetic flux of a MBSCM is sustained by the inductive superconducting current produced by the magnetizing process and is susceptible to the current intensity as well as configuration. In the HTS maglev system, the lateral displacement is an important process to change the superconducting current within a MBSCM and then affects its levitation performance, which is essential for the traffic ability in curve-way, the loading capacity of lateral impact and so on. The research about influence of lateral displacement on the levitation performance of MBSCM is necessary when MBSCM is applied on the HTS maglev vehicle. The experimental investigations about the influence of lateral displacement on the levitation performance of a MBSCM with different trapped fluxes and applied fields are processed in this article. The analyses and conclusions of this article are useful for the practical application of MBSCM in HTS maglev system.

Impurity band Mott insulators: a new route to high Tc superconductivity

Directory of Open Access Journals (Sweden)

Ganapathy Baskaran

2008-01-01

Full Text Available Last century witnessed the birth of semiconductor electronics and nanotechnology. The physics behind these revolutionary developments is certain quantum mechanical behaviour of 'impurity state electrons' in crystalline 'band insulators', such as Si, Ge, GaAs and GaN, arising from intentionally added (doped impurities. The present article proposes that certain collective quantum behaviour of these impurity state electrons, arising from Coulomb repulsions, could lead to superconductivity in a parent band insulator, in a way not suspected before. Impurity band resonating valence bond theory of superconductivity in boron doped diamond, recently proposed by us, suggests possibility of superconductivity emerging from impurity band Mott insulators. We use certain key ideas and insights from the field of high-temperature superconductivity in cuprates and organics. Our suggestion also offers new possibilities in the field of semiconductor electronics and nanotechnology. The current level of sophistication in solid state technology and combinatorial materials science is very well capable of realizing our proposal and discover new superconductors.

Trace impurity analyzer

International Nuclear Information System (INIS)

Schneider, W.J.; Edwards, D. Jr.

1979-01-01

The desirability for long-term reliability of large scale helium refrigerator systems used on superconducting accelerator magnets has necessitated detection of impurities to levels of a few ppM. An analyzer that measures trace impurity levels of condensable contaminants in concentrations of less than a ppM in 15 atm of He is described. The instrument makes use of the desorption temperature at an indicated pressure of the various impurities to determine the type of contaminant. The pressure rise at that temperature yields a measure of the contaminant level of the impurity. A LN 2 cryogenic charcoal trap is also employed to measure air impurities (nitrogen and oxygen) to obtain the full range of contaminant possibilities. The results of this detector which will be in use on the research and development helium refrigerator of the ISABELLE First-Cell is described

Intermodulation distortion and surface resistance in impurity-doped YBCO and MgB{sub 2}

Energy Technology Data Exchange (ETDEWEB)

Agassi, Y.D. [Naval Surface Warfare Center, Carderock Division, Bethesda, MD 20817 (United States); Oates, D.E., E-mail: oates@ll.mit.edu [MIT-Lincoln Laboratory, Lexington, MA 02420 (United States)

2014-11-15

Highlights: • Calculations of impurity-doping effects on surface resistance and intermodulation distortion. • The calculations are compared with previously published measurements in YBCO and MgB{sub 2}. • Excellent agreement between calculations and experiments are shown. • The effects of the symmetry of the energy gap are presented and discussed. - Abstract: Calculations of the microwave intermodulation distortion (IMD) and surface resistance of impurity-doped YBCO, MgB{sub 2} and Nb are presented. These are qualitatively distinct superconductors due to their energy-gap symmetries, d-wave (ℓ = 2), i-wave (ℓ = 6) and s-wave (ℓ = 0), respectively. The calculations are compared with previously published IMD and surface-resistance measurements of impurity-doped YBCO and Nb. The agreement between the data and fitted calculations is excellent in all cases. In the absence of IMD and surface-resistance measurements for doped MgB{sub 2}, we present representative predictions. The calculations are based on a Green’s-function approach that yields analytical expressions for the penetration depth and the nonlinear kernel in the constitutive relation. This penetration-depth expression reproduces the measured T{sup 2} low-temperature variation for doped superconductors and the surface-resistance reduction over that of the pure material. Regarding the IMD in superconductors with a nodal energy gap, the effect of doping is to enhance its magnitude and suppress its low-temperature 1/T{sup 2} divergence predicted by the nonlinear Meissner effect.

On the force relaxation in the magnetic levitation system with a high-Tc superconductor

International Nuclear Information System (INIS)

Smolyak, B M; Zakharov, M S

2014-01-01

The effect of magnetic flux creep on the lift force in a magnet/superconductor system was studied. It was shown experimentally that in the case of real levitation (when a levitating object bears only on a magnetic field) the suspension height and consequently the lift force did not change over a long period of time. When the levitating object is fixed for some time (i.e. a rigid constraint is imposed on it), the levitation height decreases after removal of the external constraint. It is assumed that free oscillations of the levitating object slow down the flux creep process, which is activated when these oscillations are suppressed. (paper)

The electronic, magnetic and optical properties of ZnO doped with doubles impurities (Cr, Fe): An LDA-SIC and Monte Carlo study

Energy Technology Data Exchange (ETDEWEB)

Salmani, El Mehdi, E-mail: elmehdisalmani@gmail.com [LMPHE, Faculté des Sciences, Université Mohammed V, Rabat (Morocco); Laghrissi, Ayoub; Lamouri, Rachida; Ez-Zahraouy, Hamid [LMPHE, Faculté des Sciences, Université Mohammed V, Rabat (Morocco); Benyoussef, Abdelilah [Institute for Nanomaterials and Nanotechnologies, MAScIR, Rabat (Morocco); Académie Hassan II des Sciences et Techniques, Rabat (Morocco)

2017-01-15

Electronic structure, magnetic and optical properties of ZnO doped with single and double impurities Zn{sub 1−x}Cr{sub x}O, Zn{sub 1−x}Fe{sub x}O, and Zn{sub 1−2x}Cr{sub x}Fe{sub x}O (x=0.03 and 0.06) are investigated using first-principles calculations. Based on the Korringa–Kohn–Rostoker method combined with the coherent potential approximation, we investigated the half-metallic ferromagnetic behavior of doubles impurities (Cr, Fe) doped ZnO. To support our results, we apply the self-interaction-corrected local density approximation (SIC-LDA) to study the electronic structure, optical and magnetic properties of Co-doped ZnO with doubles impurities (Cr, Fe) showing that the half-metallic ferromagnetic state still persists. The stability of the ferromagnetic state compared with the spin-glass state is investigated by comparing their total energies. The exchange interactions obtained from first principle calculations and used in a classical Ising model by a Monte Carlo approach resulted in ferromagnetic states with high Neel temperature. - Highlights: • The electronic structure calculations for ZnO doped with doubles impurities (Cr, Fe) have been discussed. • The half-metallic aspect was proven to take place for doubles impurities (Cr, Fe) codoped ZnO. • The doubles impurities (Cr, Fe)impurities are shown to introduce the necessary magnetic moment that makes ZnO good candidates for spintronic applications.

Iron pnictide superconductors

Energy Technology Data Exchange (ETDEWEB)

Tegel, Marcus Christian

2011-03-22

The scope of this dissertation therefore has not only been the synthesis of various new superconducting and non-superconducting iron pnictides of several structural families but also their in-depth crystallographic and physical characterisation. In Chapters 3 - 6, the family of the ZrCuSiAs-type (1111) compounds is subject of discussion. The solid solution series La(Co{sub x}Fe{sub 1-x})PO is analysed regarding magnetic and superconducting properties and the new compounds EuMnPF and REZnPO, as well as the new superconductor parent compound SrFeAsF are presented. Chapters 7 - 9 are dedicated to the new iron arsenide superconductors of the ThCr{sub 2}Si{sub 2}-type (122 family). Therein, also the discovery of the first superconductor in this structural family, Ba{sub 0.6}K{sub 0.4}Fe{sub 2}As{sub 2}, is unveiled. A detailed examination of the complete solid solution series (Ba{sub 1-x}K{sub x})Fe{sub 2}As{sub 2} is presented. Moreover, the crystallographic phase transitions of the closely related compounds SrFe{sub 2}As{sub 2} and EuFe{sub 2}As{sub 2} are characterised and the superconductors Sr{sub 1-x}K{sub x}Fe{sub 2}As{sub 2} and Ca{sub 1-x}Na{sub x}Fe{sub 2}As{sub 2} are examined for magnetic and phononic excitations. In Chapter 10, the redetermined crystal structure of the superconductor Fe(Se{sub 1-x}Te{sub x}) (11-type) is presented from a chemist's point of view. Chapters 11 - 14 look into the superconducting and non-superconducting iron arsenides of more complex structural families (32522-type and 21311-type). Therein, crystallographic and magnetic details of Sr{sub 3}Sc{sub 2}O{sub 5}Fe{sub 2}As{sub 2} are presented and Ba{sub 2}ScO{sub 3}FeAs and Sr{sub 2}CrO{sub 3}FeAs, the first two members of the new 21311-type are portrayed. Sr{sub 2}CrO{sub 3}FeAs is looked at in close detail with various methods, so e.g. the spin structure of the magnetically ordered compound is solved and a possible reason for the absence of superconductivity in this compound is

Iron pnictide superconductors

Energy Technology Data Exchange (ETDEWEB)

Tegel, Marcus Christian

2011-03-22

The scope of this dissertation therefore has not only been the synthesis of various new superconducting and non-superconducting iron pnictides of several structural families but also their in-depth crystallographic and physical characterisation. In Chapters 3 - 6, the family of the ZrCuSiAs-type (1111) compounds is subject of discussion. The solid solution series La(Co{sub x}Fe{sub 1-x})PO is analysed regarding magnetic and superconducting properties and the new compounds EuMnPF and REZnPO, as well as the new superconductor parent compound SrFeAsF are presented. Chapters 7 - 9 are dedicated to the new iron arsenide superconductors of the ThCr{sub 2}Si{sub 2}-type (122 family). Therein, also the discovery of the first superconductor in this structural family, Ba{sub 0.6}K{sub 0.4}Fe{sub 2}As{sub 2}, is unveiled. A detailed examination of the complete solid solution series (Ba{sub 1-x}K{sub x})Fe{sub 2}As{sub 2} is presented. Moreover, the crystallographic phase transitions of the closely related compounds SrFe{sub 2}As{sub 2} and EuFe{sub 2}As{sub 2} are characterised and the superconductors Sr{sub 1-x}K{sub x}Fe{sub 2}As{sub 2} and Ca{sub 1-x}Na{sub x}Fe{sub 2}As{sub 2} are examined for magnetic and phononic excitations. In Chapter 10, the redetermined crystal structure of the superconductor Fe(Se{sub 1-x}Te{sub x}) (11-type) is presented from a chemist's point of view. Chapters 11 - 14 look into the superconducting and non-superconducting iron arsenides of more complex structural families (32522-type and 21311-type). Therein, crystallographic and magnetic details of Sr{sub 3}Sc{sub 2}O{sub 5}Fe{sub 2}As{sub 2} are presented and Ba{sub 2}ScO{sub 3}FeAs and Sr{sub 2}CrO{sub 3}FeAs, the first two members of the new 21311-type are portrayed. Sr{sub 2}CrO{sub 3}FeAs is looked at in close detail with various methods, so e.g. the spin structure of the magnetically ordered compound is solved and a possible reason for the absence of superconductivity in this compound

Room temperature superconductors

International Nuclear Information System (INIS)

Sleight, A.W.

1995-01-01

If the Holy Grail of room temperature superconductivity could be achieved, the impact on could be enormous. However, a useful room temperature superconductor for most applications must possess a T c somewhat above room temperature and must be capable of sustaining superconductivity in the presence of magnetic fields while carrying a significant current load. The authors will return to the subject of just what characteristics one might seek for a compound to be a room temperature superconductor. 30 refs., 3 figs., 1 tab

Impurity concentration limits and activation in fusion reactor structural materials

International Nuclear Information System (INIS)

Zucchetti, M.

1991-01-01

This paper examines waste management problems related to impurity activation in first-wall, shield, and magnet materials for fusion reactors. Definitions of low activity based on hands-on recycling, remote recycling, and shallow land burial waste management criteria are discussed. Estimates of the impurity concentration in low-activation materials (elementally substituted stainless steels and vanadium alloys) are reported. Impurity activation in first-wall materials turns out to be critical after a comparison of impurity concentration limits and estimated levels. Activation of magnet materials is then considered: Long-term activity is not a concern, while short-term activity is. In both cases, impurity activation is negligible. Magnet materials, and all other less flux-exposed materials, have no practical limitation on impurities in terms of induced radioactivity

Static Properties of Superconductor Journal Bearing Substator for Superconductor Flywheel Energy Storage System

International Nuclear Information System (INIS)

Park, B. J.; Jung, S. Y.; Lee, J. P.; Park, B. C.; Jeong, N. H.; Sung, T. H.; Han, Y. H.

2008-01-01

A Superconductor Flywheel Energy Storage System(SFES) mainly consists of a pair of non-contacting High Temperature Superconductor(HTS) bearings that provide very low frictional losses, a composite flywheel with high energy storage density. The HTS bearings, which offer dynamic stability without active control, are the key technology that distinguishes the SFES from other flywheel energy storage devices, and great effort is being put into developing this technology. The Superconductor Journal Bearing(SJB) mainly consists of HTS bulks and a stator, which holds the HTS bulks and also acts as a cold head. Static properties of HTS bearings provide data to solve problems which may occur easily in a running system. Since stiffness to counter vibration is the main parameter in designing an HTS bearing system, we investigate SJB magnetic force through static properties between the Permanent Magnet(PM) and HTS. We measure stiffness in static condition and the results are used to determine the optimal number of HTS bulks for a 100kWh SFES.

Pair breaking and density of states in disordered superconductors

International Nuclear Information System (INIS)

Weinkauf, A.; Zittartz, J.

1975-01-01

It is shown that pair breaking occurs in a disordered superconductor due to spatial variations of the order parameter, although the system is time reversal invariant. The pair breaking effect is reflected by the occurence of some interesting fine structure in the one particle density of states. Discrete bound states and split-off impurity bands show up in the single impurity case and for very dilute alloys, respectively. For finite alloy concentrations the calculations are done within the CPA. Although principally important, the fine structure is concentrated in an energy range too narrow to be detected experimentally. (orig.) [de

Magnetic uni- and tri-axial grain-orientation in superconductors with layered structures

International Nuclear Information System (INIS)

Horii, S.; Yamaki, M.; Ogino, H.; Maeda, T.; Shimoyama, J.

2010-01-01

We report the grain-orientation effects under a modulated rotation magnetic field for Y-based cuprate superconductors and LaFeAsO (La1111). Tri-axial orientation has been successfully achieved only for orthorhombic Y 2 Ba 4 Cu 7 O y and YBa 2 Cu 4 O 8 powders without a twin microstructure, while separation of three crystallographic axes could not be observed in twinned YBa 2 Cu 3 O y (Y123) and tetragonal La1111 powders. The morphology of grains, in addition to the symmetry of crystal structures, seriously affects the degrees of tri-axial orientation, which means that the control of twin microstructures is required for the tri-axial magnetic orientation in Y123.

Signature of magnetic-dependent gapless odd frequency states at superconductor / ferromagnet interfaces

Energy Technology Data Exchange (ETDEWEB)

Robinson, Jason [Department of Materials Science, 27 Charles Babbage Road, Cambridge, CB30FS (United Kingdom)

2015-07-01

The theory of superconductivity developed by Bardeen, Cooper, and Schrieffer (BCS) explains the stabilisation of electron pairs into a spin-singlet, even frequency, state by the formation of an energy gap below which the density of states (DoS) is zero. At a superconductor interface with an inhomogeneous ferromagnet, a gapless odd frequency superconducting state is predicted in which the Cooper pairs are in a spin-triplet state. Although indirect evidence for such a state has been obtained, the gap structure and pairing symmetry have not so far been determined. In this talk I will present scanning tunnelling spectroscopy of Nb superconducting films proximity coupled to epitaxial Ho. These measurements reveal pronounced changes to the Nb sub-gap superconducting DoS on driving the Ho through a metamagnetic transition from a helical antiferromagnetic to a homogeneous ferromagnetic state for which a BCS-like gap is recovered. The results verify odd frequency spin-triplet superconductivity at superconductor / inhomogeneous magnet interfaces.

Impurity coupled to an artificial magnetic field in a Fermi gas in a ring trap

Science.gov (United States)

Ünal, F. Nur; Hetényi, B.; Oktel, M. Ã.-.

2015-05-01

The dynamics of a single impurity interacting with a many-particle background is one of the central problems of condensed-matter physics. Recent progress in ultracold-atom experiments makes it possible to control this dynamics by coupling an artificial gauge field specifically to the impurity. In this paper, we consider a narrow toroidal trap in which a Fermi gas is interacting with a single atom. We show that an external magnetic field coupled to the impurity is a versatile tool to probe the impurity dynamics. Using a Bethe ansatz, we calculate the eigenstates and corresponding energies exactly as a function of the flux through the trap. Adiabatic change of flux connects the ground state to excited states due to flux quantization. For repulsive interactions, the impurity disturbs the Fermi sea by dragging the fermions whose momentum matches the flux. This drag transfers momentum from the impurity to the background and increases the effective mass. The effective mass saturates to the total mass of the system for infinitely repulsive interactions. For attractive interactions, the drag again increases the effective mass which quickly saturates to twice the mass of a single particle as a dimer of the impurity and one fermion is formed. For excited states with momentum comparable to number of particles, effective mass shows a resonant behavior. We argue that standard tools in cold-atom experiments can be used to test these predictions.

Bearing design for flywheel energy storage using high-TC superconductors

Science.gov (United States)

Hull, John R.; Mulcahy, Thomas M.

2000-01-01

A high temperature superconductor material bearing system (38) This system (38) includes a rotor (50) having a ring permanent magnet (60), a plurality of permanent magnets (16, 20 and 70) for interacting to generate levitation forces for the system (38). This group of magnets are a push/pull bearing (75). A high temperature superconductor structure (30) interacts with the ting permanent magnet (60) to provide stabilizing forces for the system (38).

Theory of the upper critical field in layered superconductors

International Nuclear Information System (INIS)

Klemm, R.A.; Luther, A.; Beasley, M.R.

1975-01-01

The upper critical field H/subc/ 2 in layered superconductors is calculated from a microscopic theory in which the electrons are assumed to propagate freely within the individual layers subject to scattering off impurities and to propagate via tunneling between the layers. For the magnetic field parallel to the layers, there is a temperature T* 2 /sub parallel/ is thus determined by the combined effects of Pauli paramagnetism and spin-orbit scattering, and for sufficiently strong spin-orbit scattering rates, H/subc/ 2 /sub parallel/(T =0) can greatly exceed the Chandrasekhar-Clogston Pauli limiting field H/subP/. This unusual behavior is found to be most pronounced in the dirty limit for the electron propagation within the layers and when the electrons scatter many times in a given layer before tunneling to an adjacent layer. Our results are also discussed in light of the available experimental data. (auth)

High temperature superconductor micro-superconducting-quantum-interference-device magnetometer for magnetization measurement of a microscale magnet.

Science.gov (United States)

Takeda, Keiji; Mori, Hatsumi; Yamaguchi, Akira; Ishimoto, Hidehiko; Nakamura, Takayoshi; Kuriki, Shinya; Hozumi, Toshiya; Ohkoshi, Shin-ichi

2008-03-01

We have developed a high temperature superconductor (HTS) micrometer-sized dc superconducting quantum interference device (SQUID) magnetometer for high field and high temperature operation. It was fabricated from YBa2Cu3O7-delta of 92 nm in thickness with photolithography techniques to have a hole of 4x9 microm2 and 2 microm wide grain boundary Josephson junctions. Combined with a three dimensional magnetic field coil system, the modulation patterns of critical current Ic were observed for three different field directions. They were successfully used to measure the magnetic properties of a molecular ferrimagnetic microcrystal (23x17x13 microm3), [Mn2(H2O)2(CH3COO)][W(CN)8]2H2O. The magnetization curve was obtained in magnetic field up to 0.12 T between 30 and 70 K. This is the first to measure the anisotropy of hysteresis curve in the field above 0.1 T with an accuracy of 10(-12) J T(-1) (10(-9) emu) with a HTS micro-SQUID magnetometer.

Evaluating superconductors for microwave applications

International Nuclear Information System (INIS)

Hammond, B.; Bybokas, J.

1989-01-01

It is becoming increasingly obvious that some of the earliest applications for high Tc superconductors will be in the microwave market. While this is a major opportunity for the superconductor community, it also represents a significant challenge. At DC or low frequencies a superconductor can be easily characterized by simple measurements of resistivity and magnetic susceptibility versus temperature. These parameters are fundamental to superconductor characterization and various methods exist for measuring them. The only valid way to determine the microwave characteristics of a superconductor is to measure it at microwave frequencies. It is for this reason that measuring microwave surface resistance has emerged as one of the most demanding and telling tests for materials intended for high frequency applications. In this article, the theory of microwave surface resistance is discussed. Methods for characterizing surface resistance theoretically and by practical implementation are described

Field-induced interplanar magnetic correlations in the high-temperature superconductor La1.88Sr0.12CuO4

DEFF Research Database (Denmark)

Rømer, A. T.; Jensen, P.; Jacobsen, H.

2015-01-01

We present neutron-scattering studies of the interplanar magnetic correlations in the high-temperature superconductor La1.88Sr0.12CuO4 (Tc=27 K). The correlations are studied both in a magnetic field applied perpendicular to the CuO2 planes, and in zero field under different cooling conditions. We...

Studies of the interaction between a magnet and a High Tc Superconductor

International Nuclear Information System (INIS)

Yang, Z.

1991-01-01

This dissertation consists of two parts. The last part is eight research papers which involve topics related to High T c superconductor (HTSC) studies. The main topic describes the interaction between a permanent magnet and a HTSC studied by a mechanical pendulum. The first part of the dissertation has two purposes. One is to give a brief introduction and background to the research papers, and the other is to outline the scientific findings from the HTSC studies. 94 refs., 2 figs

Computer modelling of high-temperature superconductors using an A-V formulation

Energy Technology Data Exchange (ETDEWEB)

Ruiz-Alonso, D; Coombs, T; Campbell, A M [Cambridge University Engineering Department, Trumpington Street, Cambridge, CB2 1PZ (United Kingdom)

2004-05-01

Numerical methods for calculating the current and field distribution in high-temperature superconductors under non-uniform time-varying fields are being investigated. The highly non-linear behaviour of superconductors makes them difficult to analyse and computationally expensive. This non-linear behaviour is often accounted for through a non-linear E-J constitutive law. This paper proposes a fast method based on the finite element method to solve 2D and axially symmetric problems that contain superconducting materials. An E-J power law together with an A-V formulation is used to calculate the induction of currents in the superconductor due to time-varying external magnetic fields or forced transport current. Experimental data of a magnet-above-superconductor system is obtained in order to validate the model. In the experimental set-up a magnet is brought towards a superconducting puck at different speed rates and is also vibrated on top of it. The force between the magnet and the superconductor is measured and is found to vary with both time and frequency of excitation.

Computer modelling of high-temperature superconductors using an A-V formulation

International Nuclear Information System (INIS)

Ruiz-Alonso, D; Coombs, T; Campbell, A M

2004-01-01

Numerical methods for calculating the current and field distribution in high-temperature superconductors under non-uniform time-varying fields are being investigated. The highly non-linear behaviour of superconductors makes them difficult to analyse and computationally expensive. This non-linear behaviour is often accounted for through a non-linear E-J constitutive law. This paper proposes a fast method based on the finite element method to solve 2D and axially symmetric problems that contain superconducting materials. An E-J power law together with an A-V formulation is used to calculate the induction of currents in the superconductor due to time-varying external magnetic fields or forced transport current. Experimental data of a magnet-above-superconductor system is obtained in order to validate the model. In the experimental set-up a magnet is brought towards a superconducting puck at different speed rates and is also vibrated on top of it. The force between the magnet and the superconductor is measured and is found to vary with both time and frequency of excitation

Superconductor stability, 1983: a review

International Nuclear Information System (INIS)

Dresner, L.

1983-01-01

Three main topics have been discussed in this paper, namely, internally cooled superconductors, cooling by superfluid helium, and metastable magnets. The discussion of each has centered around a dominant idea, and it is fitting to highlight these ideas by way of conclusion. With regard to internally cooled superconductors, most of what we have learned in the last few years centers on the strong motion caused by the thermal expansion of helium. How naive were our early calculations that treated the helium as though it were incompressible. Our discussion of He-II was organized around the Gorter-Mellink relation and the solutions of the nonlinear diffusion equation it gives rise to. And our discussion of metastable magnets revolved around the fruitful concept of the MPZ. These three ideas are sturdy trunks that support much of the thought about superconductor stability that has flowered in the past several years

The impurity transport in HT-6B tokamak

International Nuclear Information System (INIS)

Huang Rong; Xie Jikang; Li Linzhong; He Yexi; Wang Shuya; Deng Chuanbao; Li Guoxiang; Qiu Lijian

1992-06-01

The quasi-stationary profiles of the impurity ionization stages in HT-6B tokamak were determined by monitoring the VUV (vacuum ultraviolet) and visible line emissions from impurities. An impurity transport code was set up. The impurity transport coefficients and other parameters of impurities in that device were simulated and determined. From the measurement of impurity emission profiles and simulation analysis, it is concluded that the impurity confinement is improved and the impurity recycling is reduced by the slow magnetic compression. Some characteristics of impurity transport in that device are also discussed

Type-I and type-II topological nodal superconductors with s -wave interaction

Science.gov (United States)

Huang, Beibing; Yang, Xiaosen; Xu, Ning; Gong, Ming

2018-01-01

Topological nodal superconductors with protected gapless points in momentum space are generally realized based on unconventional pairings. In this work we propose a minimal model to realize these topological nodal phases with only s -wave interaction. In our model the linear and quadratic spin-orbit couplings along the two orthogonal directions introduce anisotropic effective unconventional pairings in momentum space. This model may support different nodal superconducting phases characterized by either an integer winding number in BDI class or a Z2 index in D class at the particle-hole invariant axes. In the vicinity of the nodal points the effective Hamiltonian can be described by either type-I or type-II Dirac equations, and the Lifshitz transition from type-I nodal phases to type-II nodal phases can be driven by external in-plane magnetic fields. We show that these nodal phases are robust against weak impurities, which only slightly renormalizes the momentum-independent parameters in the impurity-averaged Hamiltonian, thus these phases are possible to be realized in experiments with real semi-Dirac materials. The smoking-gun evidences to verify these phases based on scanning tunneling spectroscopy method are also briefly discussed.

Performance boundaries in Nb3Sn superconductors

NARCIS (Netherlands)

Godeke, A.

2005-01-01

Superconducting magnets for High Energy Physics, Fusion, Magnetic Resonance Imaging (NMR) and Nuclear Magnetic Resonance, benefit from the extremely high current densities that can be achieved in superconductors compared to normal conducting materials. These magnets are usually constructed starting

Temperature dependence of the magnetic hyperfine field at an s–p impurity diluted in RNi_2

International Nuclear Information System (INIS)

Oliveira, A.L. de; Chaves, C.M.; Oliveira, N.A. de; Troper, A.

2016-01-01

We study the formation of local magnetic moments and magnetic hyperfine fields at an s–p impurity diluted in intermetallic Laves phase compounds RNi_2 (R=Nd, Sm, Gd, Tb, Dy) at finite temperatures. We start with a clean host and later the impurity is introduced. The host has two-coupled (R and Ni) sublattice Hubbard Hamiltonians but the Ni sublattice can be disregarded because its d band, being full, is magnetically ineffective. Also, the effect of the 4f electrons of R is represented by the polarization they produce on the d band. This leaves us with a lattice of effective rare earth R-ions with polarized electrons. For the dd electronic interaction we use the Hubbard–Stratonovich identity in a functional integral approach in the static saddle point approximation. - Highlights: • Functional integral method in the static limit, producing site disorder, is used. • The site disorder is treated with the Coherent Potential Approximation (CPA). • Non magnetic Ni generates an effective lattice with only a polarized R d band. • The effective R lattice differ from the pure R metal: Results and Discussions. • The experimental curve of hyperfine fields × temperature are very well reproduced.

Flux motion in Y-Ba-Cu-O bulk superconductors during pulse field magnetization

International Nuclear Information System (INIS)

Yoshizawa, K; Nariki, S; Sakai, N; Murakami, M; Hirabayasi, I; Takizawa, T

2004-01-01

We have studied the relationship between the magnetization and temperature change in Y-Ba-Cu-O bulk superconductor during pulse field magnetization (PFM). The flux motion was monitored using both Hall sensors and pick-up coils that are placed on a surface of a Y-Ba-Cu-O disc having dimensions of 15 mm in diameter and 0.95 mm in thickness. The peak value of the field was varied from 0.2 to 0.8 T. The effect of the static bias field was also studied in the range of 0-3 T. The temperature of the sample surface was measured using a resistance temperature sensor. The temperature increased with the magnitude of the applied pulsed magnetic field, and the amount of temperature rise decreased with increasing static bias field

Hyperfine magnetic fields for 5d impurities in iron: pre-equilibrium effects, texture and the Aharoni effect

International Nuclear Information System (INIS)

Stuchbery, A.E.; Bezakova, E.

1998-01-01

Static magnetic hyperfine fields acting on impurities recoil-implanted into ferromagnetic hosts following heavy-ion induced reactions have been studied using the implantation perturbed angular correlation (IMPAC) technique to determine the magnetic moments of subnanosecond excited states in neutron-deficient nuclei. Problems, which in time-integral measurements cannot always be treated independently were studied and include: (i) corrections for the transient field effect, (ii) whether the hyperfine field is parallel to the applied field, (iii) whether the implanted nuclei all experience the same magnetic interaction, (iv) the time the static field takes to reach equilibrium after implantation. The focus here is on pre-equilibrium phenomena associated with the implantation process and the direction of the internal magnetic field at implanted impurities after equilibrium is reached. It was found that the internal field does become increasingly misaligned with respect to external field direction at fields below 0.08 T. This is due to the incomplete saturation of the foil and not to the microscopic effect as proposed by Aharoni

Pulsed-Field Magnetization Properties of Bulk Superconductors by Employment of Vortex-Type Coils

Science.gov (United States)

Deng, Z.; Shinohara, N.; Miki, M.; Felder, B.; Tsuzuki, K.; Watasaki, M.; Kawabe, S.; Taguchi, R.; Izumi, M.

Vortex-type magnetizing coils are gaining more and more attention to activate bulk superconductors in pulsed-field magnetization (PFM) studies, compared with solenoid-type ones. Following existing reports, we present experimental results of the different penetration patterns of magnetic flux between the two kinds of coils. It was found that the magnetic flux will primarily penetrate inside the bulk from the upper and lower surfaces by using vortex coils, rather than from the periphery in the case of solenoid coils. Moreover, the bulk submitted to a small pulsed-field excitation exhibits a similar field profile as the excitation field (convex or concave shape); a phenomenon named field memory effect. The use of vortex- or solenoid-type coils in PFM will pose an influence on the initial flux penetration patterns during the flux trapping processes, but both coils can finally excite the best conical trapped field shape of the bulk.

Quantum theory of an atom in proximity to a superconductor

Science.gov (United States)

Le Dall, Matthias; Diniz, Igor; Dias da Silva, Luis G. G. V.; de Sousa, Rogério

2018-02-01

The impact of superconducting correlations on localized electronic states is important for a wide range of experiments in fundamental and applied superconductivity. This includes scanning tunneling microscopy of atomic impurities at the surface of superconductors, as well as superconducting-ion-chip spectroscopy of neutral ions and Rydberg states. Moreover, atomlike centers close to the surface are currently believed to be the main source of noise and decoherence in qubits based on superconducting devices. The proximity effect is known to dress atomic orbitals in Cooper-pair-like states known as Yu-Shiba-Rusinov (YSR) states, but the impact of superconductivity on the measured orbital splittings and optical-noise transitions is not known. Here we study the interplay between orbital degeneracy and particle-number admixture in atomic states, beyond the usual classical spin approximation. We model the atom as a generalized Anderson model interacting with a conventional s -wave superconductor. In the limit of zero on-site Coulomb repulsion (U =0 ), we obtain YSR subgap energy levels that are identical to the ones obtained from the classical spin model. When Δ is large and U >0 , the YSR spectra are no longer quasiparticle-like, and the highly degenerate orbital subspaces are split according to their spin, orbital, and number-parity symmetry. We show that U >0 activates additional poles in the atomic Green's function, suggesting an alternative explanation for the peak splittings recently observed in scanning tunneling microscopy of orbitally-degenerate impurities in superconductors. We describe optical excitation and absorption of photons by YSR states, showing that many additional optical channels open up in comparison to the nonsuperconducting case. Conversely, the additional dissipation channels imply increased electromagnetic noise due to impurities in superconducting devices.

Critical current enhancement by Lorentz force reduction in superconductor-ferromagnet nanocomposites

International Nuclear Information System (INIS)

Blamire, M G; Dinner, R B; Wimbush, S C; MacManus-Driscoll, J L

2009-01-01

Ferromagnetic pinning centres in superconductors form much deeper potential wells than equivalent insulating or metallic non-superconducting inclusions. However, the resultant pinning forces arising from magnetic inclusions are low because the magnetic interaction takes place over the length scale of the magnetic penetration depth which is large in technological superconductors. Nonetheless, we show that a magnetic inclusion can also reduce the Lorentz force on a vortex, yielding a substantially enhanced critical current density for a given pinning force. We calculate this enhancement for a single vortex pinned by a paramagnetic cylinder as well as a vortex lattice interacting with magnetic inclusions, and find that the inclusion of ferromagnetic particles or rods offers a practical means of enhancing the critical currents in oxide high temperature superconductors.

Critical Current Properties in Longitudinal Magnetic Field of YBCO Superconductor with APC

Science.gov (United States)

Kido, R.; Kiuchi, M.; Otabe, E. S.; Matsushita, T.; Jha, A. K.; Matsumoto, K.

The critical current density (Jc) properties of the Artificial Pinning Center (APC) introduced YBa2Cu3O7 (YBCO) films in the longitudinal magnetic field were measured. Y2O3 or Y2BaCuO5 (Y211) was introduced as APCs to YBCO, and YBCO films with APC were fabricated on SrTiO3 single crystal substrate. The sizes of Y2O3 and Y211 were 5-10 nm and 10-20 nm, respectively. As a result, Jc enhancement in the longitudinal magnetic field was observed in Y2O3 introduced YBCO films. However, it was not observed in Y211 introduced YBCO films. Therefore, it was considered that Jc properties in the longitudinal magnetic field were affected by introducing of small size APC, and it was necessary that APC does not disturb the current pathway in the superconductor.

The superconductor revolutions and the (slow) applications evolution

International Nuclear Information System (INIS)

Foner, S.

1990-01-01

The discovery in the 1960's of type 2 superconductors with high critical current densities in high magnetic fields (and the development of NbTi in particular) led to the first revolution. The discovery of high temperature superconductors (HTS) started the second revolution. At this stage ceramists became involved with superconductors. I will assess the status of various superconductor applications, progress of HTS and their possible applications at 4.2K, and near-term needs for superconducting materials operating at 30T in specialized facilities. Reasons for the slow growth of superconductor applications will be reviewed

Microwave impedance of epitaxial high-temperature superconductor films

International Nuclear Information System (INIS)

Melkov, G.A.; Malyshev, V.Yu.; Bagada, A.V.

1995-01-01

In the 3 cm band dependences of the epitaxial HTS film surface resistance on the magnitude of ac and dc magnetic fields have been measured. YBa 2 Cu 3 O 7-σ films on sapphire were investigated. It was established that alternating magnetic field produces a stronger impact on the surface resistance than dc field. To explain experimental results the assumption is made that a HTS film is not an ideal superconductor and consists of series-connected sections of various types: sections of an ideal superconductor, sections of low and large resistance intragranular Josephson junctions, shunted by the ideal superconductor, and finally, sections of intergranular Josephson junctions few for epitaxial films. In these conditions the dependences of the surface resistance on dc magnetic field are caused by Abrikosov's vortices moving in ideal superconductive sections, and dependences on the amplitude of ac magnetic field are caused by switching of large resistance junctions to a low resistance state

The dynamics of magnetic vortices in type II superconductors with pinning sites studied by the time dependent Ginzburg–Landau model

Energy Technology Data Exchange (ETDEWEB)

Sørensen, Mads Peter, E-mail: mpso@dtu.dk [Department of Applied Mathematics and Computer Science, Richard Petersens Plads, Bldg. 324, Technical University of Denmark, Kongens Lyngby DK-2800 (Denmark); Pedersen, Niels Falsig [Department of Applied Mathematics and Computer Science, Richard Petersens Plads, Bldg. 324, Technical University of Denmark, Kongens Lyngby DK-2800 (Denmark); Ögren, Magnus [School of Science and Technology, Örebro University, Örebro SE-70182 (Sweden)

2017-02-15

We investigate the dynamics of magnetic vortices in type II superconductors with normal state pinning sites using the Ginzburg–Landau equations. Simulation results demonstrate hopping of vortices between pinning sites, influenced by external magnetic fields and external currents. The system is highly nonlinear and the vortices show complex nonlinear dynamical behaviour.

Magnetically leviated superconducting bearing

Science.gov (United States)

Weinberger, Bernard R.; Lynds, Jr., Lahmer

1993-01-01

A magnetically levitated superconducting bearing includes a magnet (2) mounted on a shaft (12) that is rotatable around an axis of rotation and a Type II superconductor (6) supported on a stator (14) in proximity to the magnet (2). The superconductor (6) is positioned so that when it is cooled to its superconducting state in the presence of a magnetic field, it interacts with the magnet (2) to produce an attractive force that levitates the magnet (2) and supports a load on the shaft (12). The interaction between the superconductor (6) and magnet(2) also produces surface screening currents (8) that generate a repulsive force perpendicular to the load. The bearing also has means for maintaining the superconductor at a temperature below its critical temperature (16, 18). The bearing could also be constructed so the magnet (2) is supported on the stator (14) and the superconductor (6) is mounted on the shaft (12). The bearing can be operated by cooling the superconductor (6) to its superconducting state in the presence of a magnetic field.

High temperature superconductor current leads

International Nuclear Information System (INIS)

Zeimetz, B.; Liu, H.K.; Dou, S.X.

1996-01-01

Full text: The use of superconductors in high electrical current applications (magnets, transformers, generators etc.) usually requires cooling with liquid Helium, which is very expensive. The superconductor itself produces no heat, and the design of Helium dewars is very advanced. Therefore most of the heat loss, i.e. Helium consumption, comes from the current lead which connects the superconductor with its power source at room temperature. The current lead usually consists of a pair of thick copper wires. The discovery of the High Temperature Superconductors makes it possible to replace a part of the copper with superconducting material. This drastically reduces the heat losses because a) the superconductor generates no resistive heat and b) it is a very poor thermal conductor compared with the copper. In this work silver-sheathed superconducting tapes are used as current lead components. The work comprises both the production of the tapes and the overall design of the leads, in order to a) maximize the current capacity ('critical current') of the superconductor, b) minimize the thermal conductivity of the silver clad, and c) optimize the cooling conditions

Nonlocal electrodynamics and low-temperature magnetization of clean high-κ superconductors

International Nuclear Information System (INIS)

Kogan, V.G.; Gurevich, A.; Cho, J.H.; Johnston, D.C.; Xu, M.; Thompson, J.R.; Martynovich, A.

1996-01-01

We show that magnetic properties of clean superconductors with a large Ginzburg-Landau parameter κ at low temperatures are affected by the nonlocality of the microscopic current-field relation and can be described by modified London equations. We argue that for clean materials at low temperatures, the standard London formula for the reversible magnetization in intermediate fields, M∼ln(H c2 /B), should contain the field H 0 ∼φ 0 /ρ 2 instead of H c2 ∼φ 0 /ξ 2 (T), with ρ being the nonlocality range on the order of ξ 0 , the zero-T coherence length. Since ρ depends weakly on T, the magnetization should exhibit an approximate scaling M(T,B)=X(T)Y(B) as observed in Bi- and Tl-based compounds in a broad temperature domain well below T c . Our expression for the magnetization reduces to the standard London result near T c and at any temperature for the dirty case. Implications of our results for interpretation of neutron scattering data and for procedures of extracting the penetration depth are discussed. copyright 1996 The American Physical Society

Symmetry transition via tetravalent impurity and investigations on magnetic properties of Li0.5Fe2.5O4

Science.gov (United States)

Kounsalye, Jitendra S.; Kharat, Prashant B.; Chavan, Apparao R.; Humbe, Ashok V.; Borade, R. M.; Jadhav, K. M.

2018-04-01

The present study, deals with the phase symmetry transformation of lithium ferrite after introducing tetravalent (Ti4+) impurity. The sol-gel auto combustion technique was adopted for the synthesis of nanoparticle samples with generic chemical formula Li0.5Fe2.5O4 and Li0.55Ti0.10Fe2.35O4. The synthesized nanoparticles were characterized by X-ray diffraction (XRD) technique for structural analysis. The XRD patterns show the single phase cubic structure without any impurity phase but the P4332 to Fd-3m transformation was observed after introducing Ti4+ impurity. The Nano size of the synthesized particles was confirmed by crystallite size ( 20nm) calculated using Debye-Scherrer's formula. The Fourier transform infrared spectroscopy (FTIR) studies shows shifting of band frequencies which reflect the structural changes after tetravalent substitutional impurities. The magnetic properties were studied through pulse field hysteresis loop (M-H loop) technique at room temperature, the M-H loops showdecrease in magnetic properties afternonmagnetic Ti4+ ion substitution. This is attributed to transition of inverse spinel structure of lithium ferrite to random spinel structure.

Spatial Distortion of Vibration Modes via Magnetic Correlation of Impurities

Science.gov (United States)

Krasniqi, F. S.; Zhong, Y.; Epp, S. W.; Foucar, L.; Trigo, M.; Chen, J.; Reis, D. A.; Wang, H. L.; Zhao, J. H.; Lemke, H. T.; Zhu, D.; Chollet, M.; Fritz, D. M.; Hartmann, R.; Englert, L.; Strüder, L.; Schlichting, I.; Ullrich, J.

2018-03-01

Long wavelength vibrational modes in the ferromagnetic semiconductor Ga0.91 Mn0.09 As are investigated using time resolved x-ray diffraction. At room temperature, we measure oscillations in the x-ray diffraction intensity corresponding to coherent vibrational modes with well-defined wavelengths. When the correlation of magnetic impurities sets in, we observe the transition of the lattice into a disordered state that does not support coherent modes at large wavelengths. Our measurements point toward a magnetically induced broadening of long wavelength vibrational modes in momentum space and their quasilocalization in the real space. More specifically, long wavelength vibrational modes cannot be assigned to a single wavelength but rather should be represented as a superposition of plane waves with different wavelengths. Our findings have strong implications for the phonon-related processes, especially carrier-phonon and phonon-phonon scattering, which govern the electrical conductivity and thermal management of semiconductor-based devices.

Correction between B and H, and the analysis of the magnetization into uniaxial superconductor in the limit at large values of B

International Nuclear Information System (INIS)

Oliveira, I.G. de.

1994-04-01

Using the London theory, a correction is obtained between the direction of the magnetic induction B and the applied magnetic field H in superconductors with uniaxial anisotropy when the Ginsburg-Landau constant is not so large. One analysis of the magnetization as function of angle α is made. (author). 5 refs, 2 figs

Correction between B and H, and the analysis of the magnetization into uniaxial superconductor in the limit at large values of B

Energy Technology Data Exchange (ETDEWEB)

Oliveira, I.G. de

1994-04-01

Using the London theory, a correction is obtained between the direction of the magnetic induction B and the applied magnetic field H in superconductors with uniaxial anisotropy when the Ginsburg-Landau constant is not so large. One analysis of the magnetization as function of angle {alpha} is made. (author). 5 refs, 2 figs.

Development of superconducting magnetic bearing using superconducting coil and bulk superconductor

Energy Technology Data Exchange (ETDEWEB)

Seino, H; Nagashima, K; Arai, Y [Railway Technical Research Institute, Hikari-cho 2-8-38, Kokubunji-shi, Tokyo (Japan)], E-mail: seino@rtri.or.jp

2008-02-01

The authors conducted a study on superconducting magnetic bearing, which consists of superconducting rotor and stator to apply the flywheel energy-storage system for railways. In this study, high temperature bulk superconductor (HTS bulk) was combined with superconducting coils to increase the load capacity of the bearing. In the first step of the study, the thrust rolling bearing was selected for application by using liquid nitrogen cooled HTS bulk. 60mm-diameter HTS bulks and superconducting coil which generated a high gradient of magnetic field by cusp field were adopted as a rotor and a stator for superconducting magnetic bearing, respectively. The results of the static load test and the rotation test, creep of the electromagnetic forces caused by static flux penetration and AC loss due to eccentric rotation were decreased to the level without any problems in substantial use by using two HTS bulks. In the result of verification of static load capacity, levitation force (thrust load) of 8900N or more was supportable, and stable static load capacity was obtainable when weight of 460kg was levitated.

Development of superconducting magnetic bearing using superconducting coil and bulk superconductor

International Nuclear Information System (INIS)

Seino, H; Nagashima, K; Arai, Y

2008-01-01

The authors conducted a study on superconducting magnetic bearing, which consists of superconducting rotor and stator to apply the flywheel energy-storage system for railways. In this study, high temperature bulk superconductor (HTS bulk) was combined with superconducting coils to increase the load capacity of the bearing. In the first step of the study, the thrust rolling bearing was selected for application by using liquid nitrogen cooled HTS bulk. 60mm-diameter HTS bulks and superconducting coil which generated a high gradient of magnetic field by cusp field were adopted as a rotor and a stator for superconducting magnetic bearing, respectively. The results of the static load test and the rotation test, creep of the electromagnetic forces caused by static flux penetration and AC loss due to eccentric rotation were decreased to the level without any problems in substantial use by using two HTS bulks. In the result of verification of static load capacity, levitation force (thrust load) of 8900N or more was supportable, and stable static load capacity was obtainable when weight of 460kg was levitated

Magnetic relaxation induced by transverse flux shaking in MgB{sub 2} superconductors

Energy Technology Data Exchange (ETDEWEB)

Luzuriaga, J; Nieva, G; Serquis, A; Serrano, G [Centro Atomico Bariloche, CNEA, Instituto Balseiro, UNC (Argentina); BadIa-Majos, A [Departamento de Fisica de la Materia Condensada-ICMA, Universidad de Zaragoza-CSIC (Spain); Giordano, J L [Departamento de Ciencias de la IngenierIa, Universidad de Talca (Chile); Lopez, C [Departamento de Matematicas, Universidad de Alcala de Henares (Spain)], E-mail: luzuriag@cab.cnea.gov.ar

2009-01-15

We report on measurements and numerical simulations of the behavior of MgB{sub 2} superconductors when magnetic field components are applied along mutually perpendicular directions. By closely matching the geometry in simulations and measurements, full quantitative agreement is found. The critical state theory and a single phenomenological law, i.e. the field dependence of the critical current density J{sub c}(B), are sufficient for a full quantitative description of the measurements. These were performed in thick strips of carbon nanotube doped MgB{sub 2} samples. Magnetization was measured in two orthogonal directions using a SQUID magnetometer. Magnetic relaxation effects induced by the application of an oscillatory perpendicular field were observed and simulated numerically. The measurements confirm the numerical predictions, that two relaxation regimes appear, depending on the amplitude of the applied magnetic field. The overall agreement constitutes a convincing validation of the critical state model and the numerical procedures used.

Superfluid response in heavy fermion superconductors

Science.gov (United States)

Zhong, Yin; Zhang, Lan; Shao, Can; Luo, Hong-Gang

2017-10-01

Motivated by a recent London penetration depth measurement [H. Kim, et al., Phys. Rev. Lett. 114, 027003 (2015)] and novel composite pairing scenario [O. Erten, R. Flint, and P. Coleman, Phys. Rev. Lett. 114, 027002 (2015)] of the Yb-doped heavy fermion superconductor CeCoIn5, we revisit the issue of superfluid response in the microscopic heavy fermion lattice model. However, from the literature, an explicit expression for the superfluid response function in heavy fermion superconductors is rare. In this paper, we investigate the superfluid density response function in the celebrated Kondo-Heisenberg model. To be specific, we derive the corresponding formalism from an effective fermionic large- N mean-field pairing Hamiltonian whose pairing interaction is assumed to originate from the effective local antiferromagnetic exchange interaction. Interestingly, we find that the physically correct, temperature-dependent superfluid density formula can only be obtained if the external electromagnetic field is directly coupled to the heavy fermion quasi-particle rather than the bare conduction electron or local moment. Such a unique feature emphasizes the key role of the Kondo-screening-renormalized heavy quasi-particle for low-temperature/energy thermodynamics and transport behaviors. As an important application, the theoretical result is compared to an experimental measurement in heavy fermion superconductors CeCoIn5 and Yb-doped Ce1- x Yb x CoIn5 with fairly good agreement and the transition of the pairing symmetry in the latter material is explained as a simple doping effect. In addition, the requisite formalism for the commonly encountered nonmagnetic impurity and non-local electrodynamic effect are developed. Inspired by the success in explaining classic 115-series heavy fermion superconductors, we expect the present theory will be applied to understand other heavy fermion superconductors such as CeCu2Si2 and more generic multi-band superconductors.

Influence of lateral displacement on the levitation performance of a magnetized bulk high-T{sub c} superconductor magnet

Energy Technology Data Exchange (ETDEWEB)

Liu, W., E-mail: tonny-violet@163.com [College of Nuclear Technology and Automation Engineering, Chengdu University of Technology, Chengdu 610059 (China) and Applied Superconductivity Laboratory, Southwest Jiaotong University, Chengdu 610031 (China); Wang, J.S.; Ma, G.T.; Zheng, J. [Applied Superconductivity Laboratory, Southwest Jiaotong University, Chengdu 610031 (China); State Key Laboratory of Traction Power, Southwest Jiaotong University, Chengdu 610031 (China); National Laboratory of Rail Transit, Chengdu, 610031 (China); Tuo, X.G.; Li, L.L. [College of Nuclear Technology and Automation Engineering, Chengdu University of Technology, Chengdu 610059 (China); Ye, C.Q.; Liao, X.L. [Applied Superconductivity Laboratory, Southwest Jiaotong University, Chengdu 610031 (China); National Laboratory of Rail Transit, Chengdu, 610031 (China); Wang, S.Y. [Applied Superconductivity Laboratory, Southwest Jiaotong University, Chengdu 610031 (China); State Key Laboratory of Traction Power, Southwest Jiaotong University, Chengdu 610031 (China); National Laboratory of Rail Transit, Chengdu, 610031 (China)

2012-03-15

Compared with the permanent magnet, the magnetized bulk high-T{sub c} superconductor magnet (MBSCM) can trap higher magnetic field due to its strong flux pinning ability, so it is a good candidate to improve the levitation performance of high-T{sub c} superconductive (HTS) maglev system. The trapped magnetic flux of a MBSCM is sustained by the inductive superconducting current produced by the magnetizing process and is susceptible to the current intensity as well as configuration. In the HTS maglev system, the lateral displacement is an important process to change the superconducting current within a MBSCM and then affects its levitation performance, which is essential for the traffic ability in curve-way, the loading capacity of lateral impact and so on. The research about influence of lateral displacement on the levitation performance of MBSCM is necessary when MBSCM is applied on the HTS maglev vehicle. The experimental investigations about the influence of lateral displacement on the levitation performance of a MBSCM with different trapped fluxes and applied fields are processed in this article. The analyses and conclusions of this article are useful for the practical application of MBSCM in HTS maglev system.

The effect of resonant magnetic perturbations on the impurity transport in TEXTOR-DED plasmas

International Nuclear Information System (INIS)

Greiche, Albert Josef

2009-01-01

Thermonuclear fusion provides a new mechanism for the generation of electrical power which has the perspective to serve humanity for several millions of years. One possibility to implement fusion on earth is to magnetically confine hot deuterium tritium plasmas in so called tokamaks. The fusion reactions take place in the hot plasma core. Each of the fusion reactions between deuterium and tritium yields 17.6 MeV which can be used in the process of generating electrical power. Impurities contaminate the plasma which then is cooled down and diluted. This leads to a reduction of the fusion reactions and in consequence the energy yield. The transport behaviour of the impurities in the plasma is not fully understood up to now. Nevertheless, experiments have shown that the application of resonant magnetic perturbations (RMP) can control the impurity content in the plasma. The dynamic ergodic divertor (DED) on the tokamak Textor is able to induce static and dynamic RMPs. During the application of RMPs transient impurity transport experiments with argon have been performed and the time evolution of the impurity concentrations have been monitored. The line emission intensity of the impurities in the plasma is measured in the vacuum ultraviolet (VUV) and in the soft X-ray (SXR) with the absolutely calibrated VUV spectrometer Hexos and SXR PIN diodes, respectively. The analysis of the transient impurity transport experiments is performed with the help of the transport code Strahl. The impurity flows in Strahl are described by a combination of a diffusive and a convective flow. In the computing process the code solves the coupled set of continuity equations of each of the ionization stages of an impurity. With this method the time evolution of the impurity ion densities and the line emission intensities of the ionization stages can be computed. The adaption to the experimental measurements is performed with the help of the diffusion coefficient and the drift velocity which

Effect of hydrostatic and chemical pressure on the exchange interaction in magnetic borocarbide superconductors

Science.gov (United States)

Michor, H.; El-Hagary, M.; Naber, L.; Bauer, E.; Hilscher, G.

2000-03-01

The investigation of pair-breaking effects in magnetic rare-earth nickel borocarbide superconductors reveals a considerable increase of the magnetic exchange integral Jsf by hydrostatic as well as chemical pressure. In both, Jsf is governed by the R-C distance (or lattice constant a) and is described quantitatively by a simple phenomenological model. Thereby, just two parameters Jsf0=31 meV and ΔJsf/Δa=165 meV/Å explain well the influence of chemical pressure upon the initial depression rates of Tc in solid solutions R'1-xRxNi2B2C with R=Gd, Tb, Dy, Ho and R'=Y and Lu.

Quantitative magneto-optical investigation of superconductor/ferromagnet hybrid structures.

Science.gov (United States)

Shaw, G; Brisbois, J; Pinheiro, L B G L; Müller, J; Blanco Alvarez, S; Devillers, T; Dempsey, N M; Scheerder, J E; Van de Vondel, J; Melinte, S; Vanderbemden, P; Motta, M; Ortiz, W A; Hasselbach, K; Kramer, R B G; Silhanek, A V

2018-02-01

We present a detailed quantitative magneto-optical imaging study of several superconductor/ferromagnet hybrid structures, including Nb deposited on top of thermomagnetically patterned NdFeB and permalloy/niobium with erasable and tailored magnetic landscapes imprinted in the permalloy layer. The magneto-optical imaging data are complemented with and compared to scanning Hall probe microscopy measurements. Comprehensive protocols have been developed for calibrating, testing, and converting Faraday rotation data to magnetic field maps. Applied to the acquired data, they reveal the comparatively weaker magnetic response of the superconductor from the background of larger fields and field gradients generated by the magnetic layer.

Quantitative magneto-optical investigation of superconductor/ferromagnet hybrid structures

Science.gov (United States)

Shaw, G.; Brisbois, J.; Pinheiro, L. B. G. L.; Müller, J.; Blanco Alvarez, S.; Devillers, T.; Dempsey, N. M.; Scheerder, J. E.; Van de Vondel, J.; Melinte, S.; Vanderbemden, P.; Motta, M.; Ortiz, W. A.; Hasselbach, K.; Kramer, R. B. G.; Silhanek, A. V.

2018-02-01

We present a detailed quantitative magneto-optical imaging study of several superconductor/ferromagnet hybrid structures, including Nb deposited on top of thermomagnetically patterned NdFeB and permalloy/niobium with erasable and tailored magnetic landscapes imprinted in the permalloy layer. The magneto-optical imaging data are complemented with and compared to scanning Hall probe microscopy measurements. Comprehensive protocols have been developed for calibrating, testing, and converting Faraday rotation data to magnetic field maps. Applied to the acquired data, they reveal the comparatively weaker magnetic response of the superconductor from the background of larger fields and field gradients generated by the magnetic layer.

Antiferromagnetism and its origin in iron-based superconductors (Review Article)

International Nuclear Information System (INIS)

Ding, Ming-Cui; Zhang, Yu-Zhong; Lin, Hai-Qing

2014-01-01

In iron-based superconductors, unravelling the origin of the antiferromagnetism is a crucial step towards understanding the high-T c superconductivity as it is widely believed that the magnetic fluctuations play important roles in the formation of the Cooper pairs. Therefore, in this paper, we will briefly review experimental results related to the antiferromagnetic state in iron-based superconductors and focus on a review of the theoretical investigations which show applicability of the itinerant scenario to the observed antiferromagnetism and corresponding phase transitions in various families of the iron-based superconductors. A proposal of coupling between frustrated and un frustrated bands for understanding the reduced magnetic moment typically observed in iron pnictides is also reviewed. While all the above theoretical investigations do not rule out a possible existence of localized electrons in iron-based superconductors, these results strongly indicate a close relation between itinerant electrons and the magnetically ordered state and point out the importance of taking into account the orbital degrees of freedom.

Stress and strain effects on the properties of composite superconductors

International Nuclear Information System (INIS)

Welch, D.O.

1982-01-01

Practical superconductors for use in the production of high magnetic fields are generally in the form of composites of filaments of superconducting material embedded in a matrix of normally conducting material. Lorentz forces which arise during magnet operation are examples of sources of external stress, while internal stresses can arise during the fabrication of the composite superconductor, primarily due to differential thermal contraction between different materials in the composite. The properties of superconducting compounds are often sensitive functions of the elastic strain state in the compound; consequently there is a strong coupling between the mechanical and electrical properties of composite superconductors. The basic features of this phenomenon will be illustrated by a discussion of the properties of simple composite superconductors

Spatially resolved electronic structure inside and outside the vortex cores of a high-temperature superconductor

Science.gov (United States)

Mitrović, V. F.; Sigmund, E. E.; Eschrig, M.; Bachman, H. N.; Halperin, W. P.; Reyes, A. P.; Kuhns, P.; Moulton, W. G.

2001-10-01

Puzzling aspects of high-transition-temperature (high-Tc) superconductors include the prevalence of magnetism in the normal state and the persistence of superconductivity in high magnetic fields. Superconductivity and magnetism generally are thought to be incompatible, based on what is known about conventional superconductors. Recent results, however, indicate that antiferromagnetism can appear in the superconducting state of a high-Tc superconductor in the presence of an applied magnetic field. Magnetic fields penetrate a superconductor in the form of quantized flux lines, each of which represents a vortex of supercurrents. Superconductivity is suppressed in the core of the vortex and it has been suggested that antiferromagnetism might develop there. Here we report the results of a high-field nuclear-magnetic-resonance (NMR) imaging experiment in which we spatially resolve the electronic structure of near-optimally doped YBa2Cu3O7-δ inside and outside vortex cores. Outside the cores, we find strong antiferromagnetic fluctuations, whereas inside we detect electronic states that are rather different from those found in conventional superconductors.

Magnetic and electrical properties of Pr-doped Bi(Pb)-Sr-Ca-Cu-O superconductors

International Nuclear Information System (INIS)

Malik, A.I.; Halim, S.A.; Mohammed, S.B.; Khalid, K.; Hassan, Z.A.

1999-01-01

The effect of Praseodymium doping on the electrical and magnetic properties of the bismuth-based superconductors has been investigated. The doping was done on the Calcium site ranging from x=0.00 to 0.10. For low doping percentages x<0.03, the 2223 phase still persists. However beyond this concentration the samples were dominated by 2212 phase. These results were obtained from the measurements of temperature dependence of electrical resistance and ac susceptibility of the samples. The magnetic behavior of the doping element, Pr, (a 4f rare earth magnetic element) seemed to have deteriorated the superconducting properties of the system by breaking the electron pairing mechanism. Pr doping also deteriorates the coupling of the superconducting rains, as observed by the abrupt shift of the loss peaks towards lower temperatures. (author)

The iron pnictide superconductors an introduction and overview

CERN Document Server

Citro, Roberta

2017-01-01

This book covers different aspects of the physics of iron-based superconductors ranging from the theoretical, the numerical and computational, to the experimental ones. It starts from the basic theory modeling many-body physics in Fe-superconductors and other multi-orbital materials and drreaches up to the magnetic and Cooper pair fluctuations and nematic order. Finally, it offers a comprehensive overview of the most recent advancements in the experimental investigations of iron based superconductors. .

Recent progress in material technology on RE-Ba-Cu-O bulk superconductors

International Nuclear Information System (INIS)

Teshima, Hidekazu; Morita, Mitsuru

2011-01-01

The current status of large-grained RE-Ba-Cu-O (RE: Y or rare earth elements) bulk superconductors with excellent superconducting properties is described. Gd-Ba-Cu-O bulk superconductors can trap a very high magnetic field even if they are melt-processed in air. Although the electromagnetic force caused by the trapped field is larger for a larger sample and may break the sample, a large sample of Gd-Ba-Cu-O 46 mm in diameter has the potential of trapped magnetic fields greater than 10 T at around 40 K. In addition, single-grained bulk superconductors as large as 150 mm can be obtained using the RE compositional gradient method. Dy-Ba-Cu-O is an ideal material for current leads because it has low thermal conductivity and high critical current density at 77 K in high magnetic fields. Eu-Ba-Cu-O has low magnetic permeability, and is therefore suitable for bulk NMR applications. Progress in machining technology has made possible various bulk superconductors with complicated shapes such as coils, leading to small and strong electromagnets by stacking several coil-shaped bulk superconductors together. (author)

Spin excitations in hole-overdoped iron-based superconductors.

Science.gov (United States)

Horigane, K; Kihou, K; Fujita, K; Kajimoto, R; Ikeuchi, K; Ji, S; Akimitsu, J; Lee, C H

2016-09-12

Understanding the overall features of magnetic excitation is essential for clarifying the mechanism of Cooper pair formation in iron-based superconductors. In particular, clarifying the relationship between magnetism and superconductivity is a central challenge because magnetism may play a key role in their exotic superconductivity. BaFe2As2 is one of ideal systems for such investigation because its superconductivity can be induced in several ways, allowing a comparative examination. Here we report a study on the spin fluctuations of the hole-overdoped iron-based superconductors Ba1-xKxFe2As2 (x = 0.5 and 1.0; Tc = 36 K and 3.4 K, respectively) over the entire Brillouin zone using inelastic neutron scattering. We find that their spin spectra consist of spin wave and chimney-like dispersions. The chimney-like dispersion can be attributed to the itinerant character of magnetism. The band width of the spin wave-like dispersion is almost constant from the non-doped to optimum-doped region, which is followed by a large reduction in the overdoped region. This suggests that the superconductivity is suppressed by the reduction of magnetic exchange couplings, indicating a strong relationship between magnetism and superconductivity in iron-based superconductors.

Study of flux flow in high Tc superconductors

International Nuclear Information System (INIS)

Takacs, S.; Gomory, F.

1989-01-01

The magnetic field distribution and the hysteresis losses in superconductors with very large viscous forces are calculated for field amplitudes below and above the penetration field. Both the magnetic field and frequency dependence of the losses are changing with respect to the critical state model. The results are qualitatively confirmed by AC susceptibility measurements on YBaCuO superconductors, but the quantitative differences indicate that the flux flow effects are not so strong as expected and supposed by some theories

Resonant States in High-Temperature Superconductors with Impurities

CERN Document Server

Kovacevic, Z L; Hayn, R

2002-01-01

A microscopic theory of resonant states for the Zn-doped CuO_2 plane in superconducting phase is formulated within the effective t-J model. In the model derived from the original p-d model Zn impurities are considered as vacancies for the d states on Cu sites. In the superconducting phase in addition to the local static perturbation induced by the vacancy a dynamical perturbation appears which results in frequency-dependent perturbation matrix. By employing the T-matrix formalism for the Green functions in terms of the Hubbard operators the local density of electronic states with d-, p- and s-symmetry is calculated.

Pressure effect on iron based superconductors

International Nuclear Information System (INIS)

Arumugam, S.; Kanagaraj, M.

2011-01-01

A tuning of macroscopic thermo dynamical parameters such as temperature, pressure and volume play a crucial role in strongly correlated electron systems especially high T c superconductors, which leads to increasing conductivity as well as effective way of reducing intrinsic magnetic moments. Application of chemical and external pressure exhibits significant increases of critical temperature of recently discovered iron pnictides and chalcogenides superconductors. In this present report, we have investigated hydrostatic pressure effects on resistivity and magnetization of some 1111 type based oxypnictide superconductors such as Co doped CeFeAsO, La 0.8 Th 0.2 FeAsO, Ce 0.6 Y 0.4 FeAsO 0.8 F 0.2 and Yb doped CeFeAsO systems respectively. The initially applied pressure increases the T c and its down to lower value when beyond increasing pressure also has been observed and pressure effects on crystal structure were also discussed. From that all the obtained results reveal that controlling of magnetic instability and structure distortion at higher pressure is a dominant way to further developing of T c of these new ferropnictides compounds. (author)