MAGNETIC-PROPERTIES OF PROXIMITY-INDUCED SUPERCONDUCTING MATRIX IN MULTIFILAMENTARY WIRES

Critical current densities J(cp) of proximity-induced superconducting matrices in NbTi multifilamentary wires are estimated from measured twist-pitch dependence of magnetization. The values of J(cp) are 2-4 orders of magnitude smaller than those of the superconducting filaments and decrease rapidly by raising temperature T and magnetic field B(e). The interfilamentary spacing d(N) of submicrons results in zero screening length at measured temperatures ranging 4.5 to 8 K and the induced superconductivity is suggested to be type-II. The upper critical field B(c2p) is obtained by applying the scaling law to J(cp) data. B(c2p)'s at 4.5 K are 1.2-3.0 T for d(N) = 0.20-0.59 mum. The Cooper pair penetration length K(N)-1 estimated from the temperature dependence of B(c2p) shows the clean limit characteristic as T-1 and 0.32 mum for d(N) = 0.59 mum wire at 4.5 K. K(N)-1 estimated from the temperature dependence of J(cp) agrees consistently with those from B(c2p)(T).