Flux pinning in NbTi/Nb multilayers

We made thin film multilayers of NbTi and Nb (d/sub NbTi/=20 nm and d/sub Nb//spl ap/3-9 nm). Samples were characterized by electrical transport measurements between 4.2 K and T/sub c/, in magnetic fields up to 6 T. We present J/sub c/ as a function of the device geometry and orientation of the field. For some multilayers, J/sub c/ had a large peak whose onset occurs near /spl sim/0.2 H/sub c2/. We suggest this peak effect is caused by a softening of the tilt modulus. Measured critical current densities at 4.2 K of 16 kA/mm/sup 2/ at 3 T and 8 kA/mm/sup 2/ at 5 T are among the highest achieved in the NbTi system.< >