A. K. Pradhan

FLUX PINNING BY SUBSTITUTION IN ND1BA2CU3OY SINGLE CRYSTALS

Magnetization and magneto-transport studies have been performed on high quality Nd1Ba2Cu3Oy (Nd123) single crystals grown by traveling solvent floating zone method in a reduced oxygen partial pressure. The angle dependent magnetization scales well. The magnetization loop splits into two peaks for H∥c. The first peak disappears when the c-axis is tilted away from the field displaying the influence of twin boundary for H∥c. The magnetotransport measurement by a six-terminal configuration shows correlation of the vortices along the c-direction of the Nd123 crystal. The pinning force increases markedly in the twinned crystal in comparison to the detwinned Nd123 crystal. The above measurements along with the studies of volume pinning forces in twinned and detwinned crystals and their microstructure reveal that the interplay between the twin planes and the substitutional Nd–Ba sites are responsible for high pinning in this material, especially in the high field region.

Vortex Correlation in Bi2Sr2Ca1Cu2Ox Single Crystals with Columnar Defects

Magnetic properties have been carried out using SQUID and ac susceptometer on Bi2Sr2Ca1Cu2Ox single crystals with different matching fields BΦ, corresponding to equal numbers of vortices and defects. The angle dependence of magnetization vs temperature between magnetic field and c-axis shows that sample with low matching field has higher temperature at which the vortex starts to be unidirectional pinned. The resuhs show the presence of unidirectional flux pinning and interlayer Josephson vortex coupling. The ac susceptibility shows sharpening of transition and the persistence of vortex correlation for the magnetic field much higher than BΦ.