Improvement of the critical current density of spark plasma sintered MgB2by C60addition

We investigated the influence of fullerene (C 60 ) addition on the superconducting parameters of MgB 2 bulk samples obtained by spark plasma sintering (SPS). It was found that 1.5 wt% C 60 addition leads to the reduction of the critical temperature by a few K, whereas the magnetically determined critical current density increases by approximately one order of magnitude in an applied magnetic field H = 70 kOe at temperature T = 10 K. This indicates substitution of B by C in C 60 added MgB 2 processed by SPS, contrary to some data reported in the literature obtained using conventional methods. For our relatively large specimens, the occurrence of macroscale flux jumps was observed over a wide ( H , T ) domain. The relaxation of the irreversible magnetization suggests that the macroscale flux jumps transform into microscale flux jumps with increasing H and T .