Critical Properties of Bulk-Doped BaFe2As2 Pnictides for Magnet Design

A comprehensive study of upper critical ( H c 2 ) and irreversibility magnetic fields ( H irr ) in (Ba 0.6 K 0.4 )Fe 2 As 2 (critical temperature $T_{c} = \text{38.3 K}$ ), 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 c 2 – T ) phase diagrams with H c 2 as high as 65 T at 28 K for the K-doped samples and critical current density $(J_{c})$ measurements as high as 10 5 A/cm 2 for the smallest, submicrometer grain size samples were obtained. The high H c 2 , 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.