DISORDER-INDUCED ASYMMETRIC MAGNETIZATION IN BI2SR2CA2CU3O10

Magnetization measurements as a function of external magnetic field H- c, temperature T and time t were performed in a c-axis-oriented bulk B i2Sr2Ca2Cu3O10 compound sample with H-e applied along the preferential c-axis orientation. It is found that hysteresis loops, M(H-e), are as ymmetric with respect to the equilibrium magnetization M-eq, such that an additional magnetization Delta M-m=M-m-M-eq arises for the flux en trance, where M-m(H-e)=1/2[M+(H-e)+M-(H-e)] is the cs mean magnetizati on, and M+, M-, the magnetization corresponding to the ascending and d escending branches of the hysteresis loop, respectively. The time rela xation measurements made in H-e=1 T indicate that both M+(t) and M-(t) dependencies could be best described by the power law (M-M-infinity)s imilar to t(-beta), where M-infinity is obtained from the extrapolatio n of the relaxation law to tau=infinity. Above a 'depinning' temperatu re T-d approximate to 20 K, Delta M-m tends to zero, i.e. M-infinity()=M-eq, whereas at T <T-d, Delta M-m tends to the finite value M-g/2, and M-infinity(+)=M-eq+M-g. At the same time, M(infinity)(-)approximat e to M-eq for all temperatures. Furthermore, it is shown that both Del ta M, and M-g correlate well with the bulk vortex pinning, and that th e found asymmetry can hardly be understood within frameworks of the cl assical Bean-Livingston surface barrier model. A possible physical pic ture for the disorder (pinning) induced asymmetry of both the hysteres is loops and the time relaxation is presented.