MAGNETIC-RELAXATION IN K3C60 SUPERCONDUCTORS PREPARED WITH POTASSIUM HYDRIDE

We report an alternative method for preparing K3C60 fullerene supercon ductors. Potassium hydride (KH) is used to dope potassium into C-60 po wder. AC susceptibility and DC field-cooling susceptibility measuremen ts sl-low reasonably large diamagnetic signals in the prepared sample. Magnetic relaxation was measured on the sample and compared to that o f a second K3C60 sample prepared by doping with pure potassium. The ap parent pinning potential, U-0, of tile first K3C60 is found to be abou t 10 meV at 5 K and shows little temperature dependence up to 13 K; in contrast, U-0 of the second sample increases with temperature. The re laxation rate vs temperature curve of the first sample shows a peak at 9 K. U-0 of the KH-prepared sample is smaller than that of tile secon d sample for most temperatures. We attribute this to a more homogeneou s distribution of the potassium atoms in the KH-prepared sample than C hat of the second sample.