Transport critical current densities and n factors in mono- and multifilamentary MgB/sub 2//Fe tapes and wires using fine powders

Mono- and multifilamentary MgB/sub 2//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 j/sub c/ has been investigated. At 25 K and 1 T, j/sub c/ values close to 10/sup 5/ A/cm/sup 2/ were measured, while j/sub c/ of 10/sup 6/ A/cm/sup 2/ were extrapolated for 4.2 K/0T in our monofilamentary tape. MgB/sub 2//Fe tapes exhibit high exponential n factors for the resistive transition: n/spl ap/80 and 40 were found at 5 T and 7 T, respectively. The highest transport j/sub c/ values obtained so far in MgB/sub 2//Fe wires with 7 filaments were 1.1/spl times/10/sup 5/ A/cm/sup 2/ at 4.2 K and in a field of E2 T, which is still lower than for monofilamentary tapes. The function F/sub p//spl prop/b/sup p//spl middot/(1-b)/sup q/ has been established over the whole field range, and exhibits a maximum at F/sub p//spl cong/0.18. Improved deformation and recovering processing is expected to lead to higher j/sub c/ values.