The effect of Fe and Ru substitution on the superconductivity in MgCNi3

We report the effects of partial substitutions of the VIIIa elements: Fe (3d) and Ru (4d) in the intermetallic perovskite superconductor MgCNi3. In both the MgCNi3-Ru-x(x) and MgCNi3-Fe-x(x) systems, the superconducting critical temperature (T-C) decreases monotonically as x is increased. T-C decreases more slowly in the case of Ru, suggesting that the 3d electrons in Fe are magnetically pair breaking. This is supported by the normal state magnetic susceptibility measurements (chi), which shows that chi increases with Fe and decreases with Ru doping. No ferromagnetism is observed in either system. (C) 2004 Elsevier Ltd. All rights reserved.