Angular effects of transport critical currents in high-temperature superconductor tapes

Measurements of the critical current dependence on the angular orientation of the applied magnetic field for (Bi, Pb)2Sr2Ca2Cu3O10 (BSCCO-2223)/AgMg-sheathed, mono-core BSCCO-2223/Ag-sheathed and Bi2Sr2CaCu2O8 (BSCCO-2212) dip coat tapes are presented. We have demonstrated that the procedure of measurement is an important factor for the angular effect to show. For a magnetic field only applied during the measurement of Ic(θ) (during the rotation the magnetic field is set to zero) we have found a symmetric curve, while when the magnetic field is applied during the rotation the curve is asymmetric. Moreover, we found a large difference in the critical current value between the different procedures. From our measurements, we imply two conditions are necessary to have an angular effect: (1) the magnetic field must be applied during the rotation and (2) we have to start the rotation for a magnetic field parallel to the c-axis. The results are discussed in the context of the accommodation of vortices to planar defects and surface pinning

Intragranular and intergranular behaviour of multifilamentary Bi-2223/Ag tapes

This communication aims at reporting the superconducting properties of Bi-2223/Ag tapes determined by using various measuring techniques. First. the original samples have been characterized by electrical resistance, AC susceptibility. and DC magnetization. The transport (intergranular) critical Current vs. magnetic field was also determined at T = 77 K using pulsed currents up to 40 A. Next. the same combination of experiments as performed oil bent tapes in order to bring out relevant information concerning the strength of the intergranular coupling. The results show that intergranular and intragranular currents differ by at least one order of magnitude, Finally, additional magnetic measurements were carried out in order to determine the anisotropy ratio Jc(ab)/Jc(c), which was found to lie around 30. (C) 2002 Elsevier Science B.V. All rights reserved

Relevance of the scheme of regularization of the density-of-state fluctuation contribution in an arbitrary magnetic field

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Thermodynamic properties of chlorite and berthierine derived from calorimetric measurements

International audienceIn the context of the deep waste disposal, we have investigated the respective stabilities of two iron-bearing clay minerals: berthierine ISGS from Illinois [USA; (Al0.975FeIII0.182FeII1.422Mg0.157Li0.035Mn0.002)(Si1.332Al0.668)O-5(OH)(4)] and chlorite CCa-2 from Flagstaff Hill, California [USA; (Si2.633Al1.367)(Al1.116FeIII0.215Mg2.952FeII1.712Mn0.012Ca0.011)O-10(OH)(8)]. For berthierine, the complete thermodynamic dataset was determined at 1 bar and from 2 to 310 K, using calorimetric methods. The standard enthalpies of formation were obtained by solution-reaction calorimetry at 298.15 K, and the heat capacities were measured by heat-pulse calorimetry. For chlorite, the standard enthalpy of formation is measured by solution-reaction calorimetry at 298.15 K. This is completing the entropy and heat capacity obtained previously by Gailhanou et al. (Geochim Cosmochim Acta 73:4738-4749, 2009) between 2 and 520 K, by using low-temperature adiabatic calorimetry and differential scanning calorimetry. For both minerals, the standard entropies and the Gibbs free energies of formation at 298.15 K were then calculated. An assessment of the measured properties could be carried out with respect to literature data. Eventually, the thermodynamic dataset allowed realizing theoretical calculations concerning the berthierine to chlorite transition. The latter showed that, from a thermodynamic viewpoint, the main factor controlling this transition is probably the composition of the berthierine and chlorite minerals and the nature of the secondary minerals rather than temperatur

Facile Microwave Process in Water for the Fabrication of Magnetic Nanorods

1 - ArticleMagnetic nanorods were successfully prepared in water by a simple and fast method through microwave (MW) assisted reduction using akaganeite beta-FeOOH nanorods and hydrazine as precursors and reductor, respectively. Elongated paramagnetic akaganeite precursors are synthesized for the first time using dopamine as green chemical shape-control agent. The nature and the growth mechanism are identified by XRD, Raman spectroscopy and HRTEM analysis. Fast MW reduction process induces a structural and magnetic change depending on MW irradiation cycles. After 2 min, MW reduction leads to iron oxide nanorods with aspect ratio 3.2. XRD and Raman spectroscopy indicate a heterogeneous composition with high proportion of maghemite. The FMR spectrum is characteristic of shape anisotropy and weak ferromagnetic behavior is observed from SQUID measurements