[en] The melt-textured growth of Gd123 single domain was studied in air via a hot-seeding melt process. Gd-Ba substitution can be effectively suppressed by adding BaCuO_2-x. At 77 K, both J_c value at self-field and irreversibility field B_irr showed a peak with increasing the amount of BaCuO_2-x. B_irr(77 K) was higher than 7 T with a nominal composition of Gd123 + 0.33BaCuO_2-x in a molar ratio. A further addition of BaCuO_2-x deteriorated superconducting properties. A surface field of 0.7 T was trapped in a 2.5 cm single domain pellet at 77 K

[en] Single-domains of GdBa₂Cu₃O_y, (Sm_0.5Gd_0.5)Ba₂Cu₃O_y and (Sm_0.33Eu_0.33Gd_0.33)Ba₂Cu₃O_y with and without BaCuO_2-δ doping were successfully prepared under the ambient atmosphere via a two-step cooling method. At 77 K, all samples show a well-developed secondary peak effect. The combination of two-step cooling method and BaCuO_2-δ addition is very effective to suppress the LRE-Ba substitution and hence improve superconducting properties. The Gd-Ba-Cu-O samples exhibit very high J_c values, which are comparable to those of the oxygen-controlled melt-growth (OCMG) Gd-Ba-Cu-O samples

[en] Large size (Sm_0.5Eu_0.5)Ba₂Cu₃O_7-δ single domains were grown in air via a hot-seeding melt process. Superconducting properties were found to gradually enhance as the grain growth proceeds, in that the grown grain displayed low T_c and J_c values at the initial crystallization in the top center of single domain while exhibiting high T_c and J_c in the edge section. The experiment unveiled that this was mainly induced by different RE-Ba substitution levels (RE=Sm and Eu). Such a spatial modulation of composition could be effectively suppressed by employing a fast cooling in the initial growth. The modified melt growth significantly improved the field trapping ability of single domain bulks

[en] Comprehensive fractal Monte Carlo model ITMC-F (Hu and Hassanein, 2012 [1]) is developed based on the Monte Carlo ion bombardment simulation code, i.e., Ion Transport in Materials and Compounds (ITMC) code (Hassanein, 1985 [2]). The ITMC-F studies the impact of surface roughness on the angular dependence of sputtering yield. Instead of assuming material surfaces to be flat or composed of exact self-similar fractals in simulation, we developed a new method to describe the surface shapes. Random fractal surfaces which are generated by midpoint displacement algorithm and support vector machine algorithm are combined with ITMC. With this new fractal version of ITMC-F, we successfully simulated the angular dependence of sputtering yield for various ion-target combinations, with the input surface roughness exponent directly depicted from experimental data (Hu and Hassanein, 2012 [1]). The ITMC-F code showed good agreement with the experimental data. In advanced, we compare other experimental sputtering yield with the results from ITMC-F to estimate the surface roughness exponent for ion-bombarded material in this research

[en] Magnetization loops of NdBa₂Cu₃O_7-δ (Nd123) single crystals grown under low oxygen partial pressure and melt-processed (Sm_0.5Eu_0.5)Ba₂Cu₃O_7-δ (SE123) crystals with post-annealing in Ar were comparatively studied in a wide temperature and field regime. The peak field at which magnetic moment displays the maximum, exhibits a linear temperature dependence in both cases. The fitting shows a slightly lower critical temperature than bulk T_c at null applied field. The temperature dependence of the onset field from which the absolute value of magnetic moment starts to increase, indicates the dominant pinning at low fields in Nd123 single crystals is the surface barrier while the RE211/123 interfacial pinning in melt-processed SE123 crystals

[en] We fabricated c-axis oriented large grain (Sm,Eu,Gd)Ba₂Cu₃O_7-δ bulk superconductors with BaO₂ addition under 1% O₂ partial pressure in Ar. The experiment showed that BaO₂ addition significantly reduced a RE-Ba substitution, slightly hindered the coarsening of (Sm,Eu,Gd)₂BaCuO₅ inclusion, and improved the superconducting properties. An optimum adding amount was around 0.06-0.18 per mol RE123. At 77 K, the critical current density reached 83,000 A/cm² at zero field

[en] High quality (Sm,Eu,Gd)Ba₂Cu₃O_7-δ single domain superconductors were grown in air with BaCuO_2-x addition. The flux pinning was investigated with varying temperatures of Ar post-annealing and the Eu/Gd ratio in the initial composition. The amplitude of the peak effect displayed a peak when annealed at 925 deg. C in Ar while the irreversible field B_irr keeping unchanged. Eu enrichment dramatically enhanced B_irr and the peak field for the samples annealed at 925 deg. C in Ar. At 77 K B_irr was higher than 9 T in (Sm_0.33Eu_0.44Gd_0.22)Ba₂Cu₃O_7-δ. Structural characterization showed that the average size of (Sm,Eu,Gd)₂BaCuO₅ inclusions slightly decreased with increasing the Gd concentration. The scaling analysis and field dependence of superconducting transition evidenced a predominant δT_c style pinning induced by local compositional fluctuation. The evolution of flux pinning was thus attributed to variable compositional fluctuation

[en] Electron holography was applied to study the microstructure evolution of magnetic tunnelling junctions (MTJs) CoFe/AlO_x/Co annealed at different temperatures. A mean inner potential barrier was observed in the as-deposited MTJ sample, while it was changed to a potential well after a 200 deg. C or a 400 deg. C annealing. It is suggested that the oxygen atoms were redistributed during the annealing, which left metallic atoms acting as acceptors to confine the electrons, leading to the decrease of the potential of the AlO_x barrier layer. The results suggest that the electron holography may be a useful tool for the study of the microstructure of amorphous materials

[en] RuSr₂Nd_xGd_1-xCu₂O₈ samples (x=0, 0.03, 0.06 and 0.12) were synthesised by a solid state route, using mixed rare earth oxides (Nd_xGd_1-x)₂O₃, prepared by a co-precipitation method, as precursors. Magnetoresistance measurements showed that the resistive transition temperature decreased and broadened with increasing Nd doping, suggesting that Nd really entered the lattice. The resistive transition curves in applied field exhibited typical polycrystalline behaviour with two peaks in their first derivative, identified as intra and intergrain superconducting transitions. XRD data also supported the fact that Nd ion entered the Ru-1212 lattice, yielding an ordered tetragonal structure at low Nd doping level. At higher Nd concentrations, the structure becomes disordered probably due to Nd/Sr solid solution

[en] We have synthesized the La doped YBa_2-xLa_xCu₃O_y ceramic cuprates with x≤0.30 by the solid state reaction technique under the quenching temperature from 350 to 650 deg. C. X-ray diffraction and scanning electron microscopy studies indicate that all the synthesized samples contain one single phase. La is replacing for Ba at Ba-site in YBa₂Cu₃O_y. The unit cell volume varies with La content and with the quenching temperature. The thermal expansion for the unit cell volume at different quenching temperature is discussed. For the full oxidation samples the zero resistance temperature, T_c0, is almost unchanged with x≤0.20 whilst T_c0 decreases with the increase of La content for the quenched samples. The spin gap opening temperature, T_s, for all the quenched and annealing samples are determined from the temperature dependence of resistance