Coexistence of superconductivity and ferromagnetism in polycrystalline UGe2

Electrical resistivity measurements have been made under nearly hydrostatic pressure up to 18 kbar and at temperatures between 50 mK and room temperat ure on polycrystalline specimens of the ferromagnetic compound UGe2. The Cu rie temperature decreases monotonically with pressure and can no longer be identified from the electrical resistivity measurements at a critical press ure P-c similar or equal to 16 kbar. Plots of d rho /dT versus T reveal a f eature in the rho (T) curves at T-0 similar to 0.6T(C) at P = 0 kbar that d ecreases monotonically with pressure and appears to vanish near P-c. The on set of superconductivity is observed in the range 8 kbar < P < 14 kbar with a maximum onset temperature of 1.2 K at P similar to 13 kbar. The polycrys talline specimens have a residual resistivity po up to similar to3 mu Omega cm corresponding to an electron mean free path smaller than or of the orde r of the superconducting coherence length. These results suggest that high- purity specimens with long mean free paths are not necessary, at least in t he case of UGe2, in order to observe superconductivity near the critical pr essure where the magnetic ordering temperature vanishes.