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Zero and longitudinal field SR has been used to probe the magnetic state of amorphous Bi2Sr2CaCu2Ox prepared by rapid quenching from the melt. The results suggest quasi-static spin correlations between extremely dilute Cu2+ ions.Work performed while at the J J Thomson Physical Laboratory, University of Reading. 相似文献
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《Physica C: Superconductivity and its Applications》1999,311(1-2):107-121
The mechanism of Bi2Sr2CaCu2Ox (Bi-2212) crystallization from a partially molten state has been studied by means of thermal analysis, X-ray diffraction (XRD) measurement, and microstructural observation in Bi-2212/Ag tapes. Tapes have been prepared using the isothermal partial melting (IPM) method, under which partial melting and solidification are carried out at the same temperature in an nitrogen atmosphere and 20% oxygen partial pressure (p(O2)), respectively. The Bi-2212 phase crystallizes by peritectic reaction between (Sr, Ca)CuO2 (1:1 phase) and the liquid phase at processing temperatures (Tp)≥855°C. At the beginning of Bi-2212 crystallization, only the 1:1 and the liquid phases are present in tapes. The Bi-2212 nucleation occurs in the vicinity of 1:1 grains (homogeneous nucleation). This peritectic reaction progresses by recovery of oxygen in the liquid phase. In contrast, the nucleation of the Bi-2212 phase occurs heterogeneously at Tp≤850°C. The Bi-2212 phase co-exists with four Bi-free phases ((Sr, Ca)14Cu24O41 (14:24 phase), (Sr, Ca)2CuO3 (2:1 phase), (Sr, Ca)O (1:0 phase), and the 1:1 phase) and the liquid phase in the early stage of the Bi-2212 crystallization step. Since the precipitation temperature of the Bi-2212 phase is higher than 850°C, the Bi-2212 crystallization progresses by direct precipitation. The crystallization paths affect microstructure and transport critical current density (Jc) of Bi-2212 tapes. 相似文献
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Measurements of the current-voltage characteristics of micron-size bridges made of Bi2Sr2CaCu2Ox single-crystal whiskers are carried out. It is found that, at temperatures below the superconducting transition temperature, the current-voltage characteristics exhibit quasi-periodic voltage jumps with segments of constant differential resistance whose value is proportional to the jump number. For the narrowest bridges (0.5–1 ¼m), up to ten voltage jumps are observed. The result of the experiment is explained by the formation of vortex lines under the current effect. 相似文献
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《Journal of magnetism and magnetic materials》1990,92(1):L19-L24
Magnetic flux profiles in superconducting Bi2Sr2CaCu2Ox single crystals have been observed using a magnetic garnet film as a magnetic field sensor. Measurements have been performed for the “zero-field-cooled” and “field-cooled” regimes as a function of temperature and magnetic field. An analysis of the observed patterns has revealed some peculiarities in the flux trapping effects. In particular, a nonuniform magnetic structure has been directly observed in the remanent state after “field-cooled” processes. 相似文献