ANGULAR-DEPENDENCE OF CREEP IN YBCO SINGLE-CRYSTALS INVESTIGATED BY TORQUE MAGNETOMETRY

Investigations by means of torque magnetometry at 77K reveal different torque contributions in YBCO single crystals due to intrinsic anisotr opy as well as several types of crystal defects. The angular dependenc e of the irreversible part of the magnetization shows remarkable pecul iarities in comparison with other HTSC materials. In contrast to earli er results with Bi- and Tl-type materials, scaling of the magnetizatio n component parallel to the c-axis with the corresponding flux density component is only roughly fullfilled indicating deviations from twodi mensionality in YBCO. Torque relaxation measurements reveal that, depe nding on the field orientation, different relaxation laws may occur. E ffective pinning barriers extracted from the decay curves depend stron gly on the field orientation. This dependence is clearly different fro m that found in BSCCO investigated previously. Results are discussed w ith respect to the ''butterfly'' shape observed commonly for magnetiza tion curves of YBCO.