Magneto-optical investigations of Ag-sheathed Bi-2223 tapes with   ferromagnetic shielding
  An increase in the critical current and suppression of AC losses in superconducting wires and tapes with soft magnetic sheath have been predicted theoretically and confirmed experimentally. In this work we present the results of magneto-optical investigations on a series of Ag-sheathed Bi-2223 tapes with Ni coating. We visualize distributions of magnetic field at increasing external field and different temperatures, demonstrating a difference between the flux propagation in the superconductor with Ni rims and a reference sample without Ni coating. 
V. V. Yurchenko, D. V. Shantsev, Y. M. Galperin, A. K. M. Alamgir, Z.   Han, T. H. Johansen