PIT Processed ${\rm MgB}_{2}$ Thin Wires Sheathed With Stainless Steel

MgB
₂
superconducting thin wires sheathed with stainless steel (SS) have been prepared by in-situ powder-in-tube (PIT) process. Using Magnesium hydride MgB
₂
and amorphous B powders, SS sheathed MgB
₂
thin wires have been fabricated through drawing to form the round wires of 0.20 mm ~ 0.10 mm in diameter. The SS sheath of 0.1 mm in diameter was hardened to be a Vickers hardness of around 600 HV through cold-working at room temperature without annealing. The heat treatment was performed at 630°C for 5 h in Ar gas atmosphere. The SS sheath recovered the hardness of 400 HV after heat treatment. The MgB
₂
wires show the critical temperature (T
_c
) of around 35 K in onset and sharp transition of 2 K. The transport critical current (I
_c
) at 4.2 K and self-field are 40 A and 8 A for the MgB
₂
thin wires of 0.2 mm and 0.1 mm in diameter, respectively. The I
_c
values correspond to the critical current density (J
_c
) of around 4,000-5,000 A/mm
²
. The present MgB
₂
thin wires with low thermal conductivity are promising as level sensors for liquid hydrogen and current leads with small heat leakage.