Critical Properties of Bulk-Doped BaFe2As2 Pnictides for Magnet Design

A comprehensive study of upper critical (H
_c2
) and irreversibility magnetic fields (H
_irr
) in (Ba
_0.6
K
_0.4
)Fe
₂
As
₂
(critical temperature T
_c
= 38.3 K), Ba(Fe
_0.95
Ni
_0.05
)
₂
As
₂
(T
_c
= 19.2 K), Ba(Fe
_0.94
Ni
_0.06
)
₂
As
₂
(T
_c
= 18.5 K), Ba(Fe
_0.92
Co
_0.08
)
₂
As
₂
(T
_c
= 23.2 K), and Ba(Fe
_0.91
Co
_0.09
)
₂
As
₂
(T
_c
= 25.3 K) polycrystalline bulk pnictide superconductors with different average grain sizes was made in pulsed fields at the Los Alamos National Laboratory. The magnetic field-temperature (H
_c2
-T) phase diagrams with H
_c2
as high as 65 T at 28 K for the K-doped samples and critical current density (Jo) measurements as high as 105 A/cm
²
for the smallest, submicrometer grain size samples were obtained. The high H
_c2
, H
_irr
, and J
_c
data show the suitability of these materials for magnet design as their mechanical strength and random grain alignment show promise in the manufacturing of next-generation magnets.