Local magneto-optical imaging and global magnetization measurement techniques were used to visualize shielding effects in the superconducting core of MgB2 wires sheathed in ferromagnetic Fe. The magnetic shielding could provide a Meissner-like state in the superconducting core in applied magnetic fields up to ~1T. The maximum shielding fields were shown to correlate with the saturation fields of magnetization in Fe-sheaths. The shielding was found to facilitate the appearance of an over-critical state, which was capable of achieving a JC in the core which was larger, than JC in the same wire without the sheath, by a factor of ~2.

Direct Visualization of Iron Sheath Shielding Effects in MgB2 Superconducting Wires. A.V.Pan, S.Zhou, H.Liu, S.Dou: Superconductor Science and Technology, 2003, 16, L33-6