PINNING AND VORTEX LATTICE STRUCTURE IN NBTI ALLOY MULTILAYERS

We made thin film multilayers of Nb0.37Ti0.63/Nb and Nb0.37Ti0.63/Ti ( d(NbTi) = 14-27 nm and d(N) = 4-11 nm) to examine geometries and mater ials relevant to flux pinning in commercial NbTi conductors, Samples w ere characterized by transport measurements between 4.2 K and T-c, in magnetic fields nearly parallel to the layers, up to 6 T. For some mul tilayers, pinning forces had a large peak at intermediate fields whose onset occurred near similar to 0.2 H-c2, We suggest this peak effect is caused by a change in the vortex lattice structure, driven by the s trong intrinsic pinning, We have measured the highest pinning force de nsity (113 GN/m(3) at 4.2 K and 5 T) ever achieved in the NbTi system.