AC susceptibility in NbTi multifilamentary wires

AC susceptibilities of NbTi multifilamentary wires with copper matrix were measured using a SQUID magnetometer and a susceptometer in a range of temperatures 2.0-10.0 K. The DC (up to 6.0 T) and AC magnetic fields (0.05 or 1 mT, 10 Hz) were applied perpendicular to the wire axis. The upper critical fields of matrix B-c2p were obtained from the peak temperatures T, appearing in the imaginary parts of the AC susceptibilities. These values were compared with those estimated from measured twist-pitch dependence of magnetization where the scaling law was applied to the critical current densities of the proximity-induced superconducting matrix J(cp). Both results are favorably compared. (C) 2000 Elsevier Science B.V. All tights reserved.