$J_{\rm c}$ Enhancement in Nano-${\rm Si}_{3}{\rm N}_{4}$ Doped ${\rm MgB}_{2}/{\rm Fe}$ Tapes Prepared by a Short Pre-Annealing and Intermediate Rolling Process

Using our newly developed short pre-annealing and intermediate rolling process, the property of MgB
₂
/Fe tapes doped with nano-Si
₃
N
₄
particles was further improved. The highest J
_c
value at 10 T and 4.2 K reached 6310 A/cm
²
in the sample doped with 1% nano-Si
₃
N
₄
by using our new process, which was obviously higher than that of 4550 A/cm
²
obtained in the sample made via the conventional in situ PIT process. Furthermore, it was found that the improvement of J
_c
became smaller with increasing the doping concentration of nano-Si
₃
N
₄
particles. This confirmed that our new process contributed to the J
_c
enhancement mainly through increasing the core density and connectivity. Adding more nano-Si
₃
N
₄
introduced more impurities at the grain boundaries, which made our new process less effective.