MAGNETIZATION JUMPS IN YBA2CU3O7 SINGLE-CRYSTAL, UP TO 18-T

The magnetization of a large single crystal (27 mg) of YBa//2Cu//3O//7 exhibits several new features associated to the anisotropy (and sample size): for H//c axis large magnetization jumps are observed below about 15 K. The magnetization jumps are smaller, less spaced and observed only below 7 K for H PERPEND c. At high temperature the hysteresis loops, M(H), are convex lens shaped which gives a larger density of currents in high fields. The critical currents (6. 8 10**5 A/cm**2 or 2. 8 10**5A/cm**2 for H parallel or perpendicular to the c axis, at 4. 2 K) can be compared with values obtained for much smaller crystals.