No abstract

We measured the peak effect in the magnetic hysteresis loop of an untwinned YBa&Cu307 q crystal in the vicinity of the critical temperature and studied its temperature, time, and angular dependence. The location of the peak is determined by the component of the field along the c direction. The pinning force density F~(B) is scaled into a single curve for all measured isotherms (75-87 K) and time scales (4-1500 sec), and its functional form reflects the observed peak effect. The scaling field is related to the irreversibility field of oxygen-deficient regimes. The results indicate that pinning in this system is due to inhomogeneity of the oxygen deficiency and that the peak is related to the formation of a percolationlike network of reversible regimes.