Magnetic response of Y/Pb doped single-crystal Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8+d/ superconductors

The magnetic properties of Y/Pb doped single-crystal Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8+d/ have been investigated in terms of the magnetization curves measured using a SQUID magnetometer. The observed results were analyzed within the construct of the modified Kim-Anderson critical-state model, where lower critical fields H/sub cl/ and surface barriers /spl Delta/H were explicitly taken into consideration. Analyses have revealed that the magnetic response is closely correlated to the carrier concentration, and both the lower critical field and the pinning force increase with the increase of the carrier concentration in the CuO/sub 2/ plane.