Critical current density and magnetic pinning in Nb?Ti superconductor

A theory of magnetic pinning due to randomly distributed pinning centres in the form of parallel ribbons is developed. The interaction between a vortex and pinning centres is studied with an account of the magnetic field gradient near the ribbon surface. The critical current density and the average bulk pinning force are determined as a function of the magnetic field and normal phase content. A comparison with experimental data confirms the qualitative reliability of the theoretical results.