Sh. Irons et al., MAGNETIC-PROPERTIES OF SUPERCONDUCTING K3C60 AND RB3C60 SYNTHESIZED FROM LARGE SINGLE-CRYSTAL FULLERENES, Physical review. B, Condensed matter, 52(21), 1995, pp. 15517-15521
Single crystals of C-60 were doped with alkali metal (K and Rb), chara
cterized, and measured magnetically in fields up to 5 T. Detailed expe
riments show the samples to be of high quality with superconducting tr
ansition widths on the order of 1 K. Data on the field and temperature
dependences of the critical current density J(C) and H-Cl are present
ed. We find that while the general behavior is similar to that of powd
er specimens, there are significant differences when comparing magnitu
des. We attribute these differences to the fact that powder samples ha
ve much more surface area per volume than single crystals which can af
fect the determination of superconducting parameters. The critical cur
rent density also shows clear differences when compared to polycrystal
line samples. In addition, comparisons between K3C60 and Rb3C60 indica
te that defects may be more prevalent in the latter compound due to mo
re sensitive synthesis requirements.