PEAK EFFECT AND SCALING OF IRREVERSIBLE PROPERTIES IN UNTWINNED Y-BA-CU-O CRYSTALS

We measured the peak effect in the magnetic hysteresis loop of an untw inned YBa2Cu3O7-delta crystal in the vicinity of the critical temperat ure and studied its temperature, time, and angular dependence. The loc ation of the peak is determined by the component of the field along th e c direction. The pinning force density F(p)(B) is scaled into a sing le curve for all measured isotherms (75-87 K) and time scales (4-1500 sec), and its functional form reflects the observed peak effect. The s caling field is related to the irreversibility field of oxygen-deficie nt regimes. The results indicate that pinning in this system is due to inhomogeneity of the oxygen deficiency and that the peak is related t o the formation of a percolationlike network of reversible regimes.