LOWER CRITICAL-FIELD AND REVERSIBLE MAGNETIZATION OF (BI,PB)(2)SR2CA2CU3OX SUPERCONDUCTING WHISKERS

Magnetization measurements have been carried out on Pb doped Bi2Sr2Ca2 Cu3Ox (Bi-2223) whiskers with the applied field parallel to the c-axis . The temperature dependence of the first flux penetration field H-p c an be approximated by H-p(T) = H-p(0)[1 - (T/T-c)(2)] in the region T > 50 K, while it increases upward with decreasing temperature especial ly at T < 30 K due to the surface barrier. The value H-p = H-cl(0) = 1 35 G is obtained by fitting the experimental data for T > 50 K. The pe netration depth lambda(ab) (0) = 2450 Angstrom, Ginzburg-Landau parame ter kappa = 84, and thermodynamic critical field H-c(0) = 3300 G have been calculated from the H-cl(0) value together with the upper critica l field and coherence length. The penetration depth has also been eval uated from the reversible magnetization curves. lambda(ab)(-2) is a li near function of the temperature near T-c.