Virgin magnetization of a magnetically shielded superconductor wire:   theory and experiment
  On the basis of exact solutions to the London equation the magnetic moment of a type II superconductor filament surrounded by a soft-magnet environment is calculated and the procedure of extracting the superconductor contribution from magnetic measurements is suggested. Comparison of theoretical results with experiments on MgB_2/Fe wires allows estimation of the value of critical current for the first magnetic flux penetration. 
Yu.A. Genenko, S.V. Yampolskii, A.V. Pan