ANISOTROPY OF THE MAGNETIZATION OF AN OXYGEN-DEPLETED YBA2CU3O6.82 SINGLE-CRYSTAL

The zero-field-cooled magnetization M(T,H) of an oxygen-depleted YBa2C u3O6.82 single crystal has been measured below the superconducting tra nsition temperature T-c0=85 K by applying external magnetic fields H u p to 55 kOe for both H parallel to c and H perpendicular to c. Here c denotes the direction perpendicular to the Cu-O planes of this materia l. We find that the anisotropy ratio Mn-H parallel to c/M(H perpendicu lar to c), at a fixed magnetic field H, depends on the temperature T. With decreasing T, M(H parallel to c)/M(H perpendicular to c) initiall y decreases then increases below a characteristic temperature H-min, a t which M(H parallel to c)/M(H perpendicular to c) iS a minimum. It de creases again below a temperature T-max. Both T-min and T-max are foun d to decrease with increasing H. From comparison, it is suggestive tha t T-min and T-max correspond to the irreversibility temperatures T-irr for H parallel to c and H perpendicular to c, respectively.