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_e up to 6 T and AC magnetic fields b₀ (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 _clp were estimated from the peak temperatures appearing in the imaginary parts of the AC susceptibilities χ". 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_cp. Both results are favorably compared. The lower critical fields of proximity-induced superconducting matrices B_clp were estimated from the temperatures at which the real part signal χ\´ began to decrease. The temperature dependence of B_clp agrees with that of B_c2p