Direct visualization of iron sheath shielding effect in MgB_2 superconducting wires

TL;DR

This study visualizes how ferromagnetic iron sheaths shield MgB_2 superconducting wires, enabling higher critical current densities by creating a Meissner-like state up to 1T magnetic fields.

Contribution

It provides direct visualization of the iron sheath's shielding effect and links it to enhanced critical current density in MgB_2 wires, a novel insight into magnetic interactions.

Findings

Shielding creates a Meissner-like state up to ~1T.

Critical current density is doubled with iron sheath.

Shielding correlates with Fe magnetization saturation.

Abstract

Local magneto-optical imaging and global magnetization measurement techniques were used in order to visualize shielding effects in the superconducting core of MgB_2 wires sheathed by ferromagnetic iron (Fe). The magnetic shielding can provide a Meissner-like state in the superconducting core in applied magnetic fields up to ~1T. The maximum shielding fields are shown to correlate with the saturation fields of magnetization in Fe-sheaths. The shielding has been found to facilitate the appearance of an overcritical state, which is capable of achieving a critical current density (J_c) in the core which is larger than J_c in the same wire without the sheath by a factor of ~2. Other effects caused by the magnetic interaction between the sheath and the superconducting core are discussed.