Bulk 122-Type Iron-Based Superconductors Sintered Under High Pressure

Iron-based superconductors (IBSs) have excellent characteristics such as high
T
_c
and high
H
_c2
that are advantageous for tapes and wires to be used for high-field applications. 122-type IBSs such as (Ba,
A
)Fe
₂
As
₂
(
A
; Na, K) have been used for the fabrication of tapes and wires. The same properties should also be beneficial for the bulk magnet that can trap high magnetic field. In this study, we fabricated three kinds of Ba
_0.6
Na
_0.4
Fe
₂
As
₂
bulk superconductors under high pressure using hot isostatic press (HIP), hot press, and cubic press, and characterized them including their trapped magnetic fields. Among them, the bulk sintered by a cubic press under a pressure of 2.2 GPa trapped magnetic field of ∼9.97 kG on the surface, despite its small dimensions (diameter: 4.1 mm, height: 3.64 mm). Critical current density (
J
_c
) is estimated to be 81.2 kA/cm
²
at 4.2 K under self-field. Two other bulks processed by HIP (diameter: 8.4 mm, height: 6.84 mm) and hot press (diameter: 9.45 mm, height: 4.58 mm) trapped magnetic field of 7.73 kG and 8.82 kG, respectively. The expected better texturing by uniaxial hot pressing has not been realized. As new materials for IBS bulks, which can be used for wires and tapes, we have prepared Ba
_0.6
Na
_0.4-
x
K
_x
Fe
₂
As
₂
for the first time, and characterized their physical properties by fabricating round wires.