High transport and inductive critical currents in dense Fe- and Ni- clad MgB[sub 2] tapes using fine powder

Abstract

Highly dense monofilamentary MgB2/Ni and MgB2/Fe superconducting tapes with high transport critical current densities have been fabricated using a straightforward powder-in-tube (PIT) process. High density of the MgB2 core and a fine starting powder appear to be decisive factors for reaching high critical current densities. After annealing, we measured transport jc values up to 2.3×105 A/cm2 at 4.2 K in a field of 1.5 T (corresponding to an Ic of 300 A) in a MgB2/Ni tape and up to 104 A/cm2 at 4.2 K in 6.5 T in a MgB2/Fe tape. For higher currents these monofilamentary tapes quenched due to insufficient thermal stability of filament thickness above 50 μm. Thus, jc at 4.2 K, 0T can only be extrapolated, yielding a value close to 1 MA/cm2. The recrystallization during annealing leads to a densification and to jc values which are more than a factor of ∼10 higher than those measured in the as-deformed tapes. Ni shows a limited reaction with MgB2, leading to the formation of MgB2Ni reaction layers between the f...