ANISOTROPIC MAGNETIC-RELAXATION, HYSTERESIS, AND MEISSNER FRACTION IN UNTWINNED SINGLE-CRYSTAL YBA2CU3O7-DELTA PRODUCED WITHOUT APPLYING STRESS

By quenching the tetragonal phase during crystal growth of YBa2Cu3O7- and then oxygenating the crystals without mechanical stress, we obtain some essentially untwinned crystals. Magnetic measurements on such crystals, with fields applied along the a or b axis, show anisotropy. A qualitative analysis of our relaxation and hysteresis data indicates that the critical current density is higher along a than along b (the chain direction). The anisotropic Meissner percent data show that pinning is higher for fields along b than along a. © 1990 The American Physical Society.