Influence of twins on the vortex pinning in YBa2Cu3O7-δ single crystals in tilted field

In this work, we present a systematic study of magnetization hysteresis loops of twinned and detwinned YBa2Cu3O7-delta single crystals at temperatures ranging from for 4.2 to 90 K, magnetic fields up to 6 T and various angles between the applied field H and the c-axis. The samples were prepared by a conventional self-flux method and their critical temperatures were determined by using a quantum design SQUID. The magnetization measurements were carried out on a vibrating sample magnetometer. Comparison between data for the twinned and detwinned samples showed clearly the effect of twin pinning in the low and intermediate temperature region and that the pinning properties of the twin planes depend sensibly on the field orientation with respect to the crystalline axis of the sample. An attempt is made to describe the possible mechanisms governing these phenomena and conclusions concerning the twin pinning are drawn. (C) 2002 Elsevier Science B.V. All rights reserved.