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 temperature on polycrystalline specimens of the ferromagnetic compound UGe2. The Curie temperature decreases monotonically with pressure and can no longer be identified from the electrical resistivity measurements at a critical pressure P-c similar or equal to 16 kbar. Plots of d rho /dT versus T reveal a feature in the rho (T) curves at T-0 similar to 0.6T(C) at P = 0 kbar that decreases monotonically with pressure and appears to vanish near P-c. The onset 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 polycrystalline 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 order of the superconducting coherence length. These results suggest that high-purity specimens with long mean free paths are not necessary, at least in the case of UGe2, in order to observe superconductivity near the critical pressure where the magnetic ordering temperature vanishes.