AC susceptibilities in NbTi multifilamentary wires with Cu and CuMn matrices

In NbTi multifilamentary wires with Cu and CuMn matrices, AC susceptibilities were measured using a SQUID magnetometer and a PPMS susceptometer at temperatures of 2 to 10 K, DC magnetic fields B/sub e/ up to 6 T and AC magnetic fields b/sub 0/ (0.05 to 1 mT, 10 to 53 Hz). Both fields were applied perpendicular to the wire axis. The upper critical fields of proximity-induced superconducting matrices B/sub clp/ were estimated from the peak temperatures appearing in the imaginary parts of the AC susceptibilities /spl chi/". These values were compared with those estimated from measured twist-pitch dependence of magnetization where the scaling law is applied to the critical current densities of the proximity-induced superconducting matrix J/sub cp/. Both results are favorably compared. The lower critical fields of proximity-induced superconducting matrices B/sub clp/ were estimated from the temperatures at which the real part signal /spl chi/' began to decrease. The temperature dependence of B/sub clp/ agrees with that of B/sub c2p/.