We present a comparative study of the angular dependent critical current density in YBa 2 Cu 3 O 7 films deposited on IBAD MgO and on single crystal MgO and SrTiO 3 substrates. We identify three angular regimes where pinning is dominated by different types of correlated and uncorrelated defects. We show that those regimes are present in all cases, indicating that the pinning mechanisms are the same, but their extension and characteristics are sample dependent, reflecting the quantitative differences in texture and defect density. In particular, the more defective nature of the films on IBAD turns into an advantage as it results in stronger vortex pinning, demonstrating that the critical current density of the films on single crystals is not an upper limit for the performance of the IBAD coated conductors.

Zero-field muon-spin-resonance and lower-critical-field data are presented for a wide range of Th concentrations in Uix Th v Bei3, spanning the region where both a superconducting and a second, lowertemperature phase transition are observed. Overall T-x phase boundaries are assigned and discussed according to the nature of the lower phase transition. Arguments for associating the lower phase with a possible magnetic (time-reversal-violating) superconducting state are given.

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This paper presents a new finite-element simulation model for computing the electromagnetic properties and AC losses in systems of YBCO (yttrium barium copper oxide) conductors on roll assisted biaxially textured substrates (RABiTS). In this model, the magnetic field dependent permeability and ferromagnetic loss of the substrates in RABiTS YBCO tapes are taken into account. The simulations were employed to simulate the AC loss in stacks of two parallel connected YBCO tapes. The simulation results are compared with the experimental data to check the validity of the simulation model. The result reveals an effective way of significantly reducing AC loss in YBCO tapes by stacking two RABiTS YBCO coated conductors with the appropriate relative tape orientation.

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Nanocrystalline maghemite, γ–Fe2O3, can be synthesized in a microwave plasma using FeCl3 or Fe3(CO)12 as the precursor. Electron microscopy revealed particle sizes in the range of 5 to 10 nm. In general, this material is superparamagnetic. The magnetic properties are strongly dependent on the precursor. In both cases the production process leads to a highly disordered material with the consequence of a low magnetization. The assumption of a disordered structure is also supported by electron energy loss (EEL) and Mössbauer spectroscopy. The structure of this material shows a nearly identical number of cations on tetrahedral and octahedral lattice sites.

This work studies the influence of microstructures and crystalline defects on the superconductivity of MgB 2 , with the objective to improve its flux pinning. A MgB 2 sample pellet that was hot isostatic pressed (HIPed) was found to have significantly increased critical current density (J c ) at high fields than its un-HIPed counterpart. The HIPed sample had a J c of 10000 A/cm 2 in 50000 Oe (5 T) at 5K. This was 20 times higher than that of the un-HIPed sample, and the same as the best J c reported by other research groups. Microstructures observed in scanning and transmission electron microscopy indicate that the HIP process eliminated porosity present in the MgB 2 pellet resulting in an improved intergrain connectivity. Such improvement in intergrain connectivity was believed to prevent the steep J c drop with magnetic field H that occurred in the un-HIPed MgB 2 pellet at H > 45000 Oe (4.5 T) and T = 5 K. The HIP process was also found to disperse the MgO that existed at the grain boundaries of the un-HIPed MgB 2 pellet and to generate more dislocations in the HIPed the pellets. These dispersed MgO particles and dislocations improved flux pinning also at H<45000 Oe. The HIPing process was also found to lower the resistivity at room temperature.74.70. Ad, 74.60.Ge, 74.62.Bf, 74.25.Fy 1