G. Triscone et al., MAGNETIC-PROPERTIES OF THE BI1.95SR2.05-XLAXCUOY (BI-2201) SUPERCONDUCTING PHASE, Physica. C, Superconductivity, 290(3-4), 1997, pp. 188-205
We have investigated the reversible mixed-state magnetization M of thr
ee lanthanum substituted Bi1.95Sr2.05-xLaxCuOy?,, (Bi-2201) ceramic sa
mples having different critical temperatures T-c ranging from 20.0 to
35.5 K. As for the Bi2Sr2CaCu2O8+delta (Bi-2212) phase, we found that
anisotropy of Bi-2201 is large. A manifestation of this anisotropy is
the field independent magnetization M observed at a temperature T*. I
n the framework of the London model, and including thermal fluctuation
s of vortices, we found for the temperature dependence of the penetrat
ion depth lambda(ab)(T) = lambda(ab)(0)[1-(T/T-c0)(n)](-1/2), with n a
pproximate to 1.7 and lambda(ab)(T = 0) approximate to 4000 Angstrom.
The estimated upper critical fields mu(0),H-c2,H-c,,, are of the order
of 10 T. We observe a peculiar negative slope partial derivative M/pa
rtial derivative T at low temperature and sufficiently high external m
agnetic field. This feature seems to he a characteristic of the Bi-220
1 phase. However, we do not know whether it is associated with the sup
erconducting mixed-state. A small amount of magnetic impurities could
also be responsible for this behavior. Finally, the behavior of the re
versible magnetization of the Bi-2201 samples investigated, which are
situated at the optimal and in the overdoped region, did not indicate
any unusual temperature dependence for the upper critical field H-c2,H
-c. (C) 1997 Elsevier Science B.V.