The Effect of Ru substitution for Ni on the superconductivity in   MgCNi3-xRux
  The superconductor MgCNi3 has been chemically doped by partial substitution of Ru for Ni in the solid solution MgCNi3-xRux for 0<x<0.5. Magnetic and specific heat measurements show that the Sommerfeld parameter (gamma_exp) and TC decrease immediately on Ru substitution, but that a TC above 2K is maintained even for a relatively large decrease in gamma_exp. Ferromagnetism is not observed to develop through Ru substitution, and the normal state magnetic susceptibility is suppressed. 
T. Klimczuk, V. Gupta, G. Lawes, A.P. Ramirez and R.J. Cava