SUPERCONDUCTIVITY AND ANTIFERROMAGNETISM IN CR-MO-RU ALLOYS

(Cr(1-x)Mo(x))75Ru25 alloys with x = 0, 3%, 6% or 10% exhibit superconducting properties below 3 K. For low Mo concentrations comparison with theory suggests a coexistence of spin density wave antiferromagnetism and superconductivity while the spin density wave state seems to be absent at higher concentrations. Velocity of sound measurements, however, fail to reveal any spin density wave antiferromagnetic transitions in the alloys. This is attributed to two possibilities: either the nesting portions of the Fermi surface are very small or, as suggested by susceptibility measurements reported recently on Cr75Ru25, an unknown magnetic phase appears at low temperatures.