Transport critical current densities and n factors in mono- and   multifilamentary MgB2/Fe tapes and wires using fine powders
  Mono- and multifilamentary MgB2/Fe tapes and wires with high transport critical current densities have been prepared using the powder-in-tube (PIT) process. The fabrication details are described. The effect of powder grain sizes and recrystallization temperature on jc has been investigated. At 25K and 1 T, jc values close to 105 A/cm2 were measured, while jc of 106 A/cm2 were extrapolated for 4.2K/0T in our monofilamentary tape. MgB2/Fe tapes exhibit high exponential n factors for the resistive transition: n ~ 80 and 40 were found at 5 T and 7 T, respectively. The highest transport jc values obtained so far in MgB2/Fe wires with 7 filaments were 1.1 * 105 A/cm2 at 4.2 K and in a field of 2 T, which is still lower than for monofilamentary tapes. Improved deformation and recovering processing is expected to lead to higher jc values. 
H.L. Suo, P. Lezza, D. Uglietti, C. Beneduce, V. Abacherli and R.   Flukiger