Magnetization study of single crystalline K3C60 superconductors

The mixed scare parameters of single crystalline K3C60 superconductors were investigated by de magnetization measurements. Structural analyses show that the samples consist of pure K3C60 with a poor mosaic structure (3(0) FWHM). Dc magnetic measurements show 100% shielding fraction and ac magnetization results indicate that there is no granularity for current flow in the samples. The upper critical field is found to be mu(a)H(c2)(O) = 28 T and the coherence length E(O) = 3.4 nm. The results are compared to those obtained on powder and polycrystalline materials, The magnetic field dependence of the critical current density is studied and the irreversibility line is found to follow mu aH(irr) = mu(a)H(a)(1-T/T-c)(1.5). No influence of sample inhomogeneities on the temperature dependence of the upper critical field was found from measurements on samples of different quality.