Unusual Evolution From A Superconducting To An Antiferromagnetic Ground State In Y1-Xgdxpb3 (0 <= X <= 1)

We have studied the evolution of Y1-xGdxPb3 (0 <= x <= 1) from its superconducting (x = 0) to antiferromagnetic (x = 1) states with critical temperatures T-c = 4.6(2) K and T-N = 15.7(2) K, respectively. At relatively low Gd concentrations (x <= 0.03) Tc presents a weak but linear suppression with increasing x, as expected from the Abrikosov-Gorkov (AG) theory describing the Cooper pair breaking due to the exchange interaction between the impurity localized magnetic moment and the conduction electrons (ce). This linear T-c suppression rate leads to an effective exchange parameter of < J(2)(q)>(1/2)(AG) = 0.20(7) meV between the 4f localized electrons and the ce. For intermediate Gd concentrations (0.03 <= x <= 0.15), although no Gd clustering is observed, there is an unusual inflection and leveling off trend in T-c indicating that the superconducting phase persists until the highest Gd concentration in this region where magnetic interactions are evidenced by increasingly negative values of the Curie-Weiss temperature Theta(C). Analysis of low-T Gd3+ electron spin resonance (ESR) experiments and their ESR line-shape simulations, in conjunction with the trend in T-c, leads us to suggest that an exchange bottleneck mechanism between the Gd+3 localized magnetic moment and the ce may be the reason behind the inhibition of the Cooper pair-breaking mechanism, in favor of a magnetic interaction via ce polarization. Therefore, our superconducting and ESR results suggest a scenario where superconducting and magnetic phases coexist extensively in the Y1-xGdxPb3 system, mediated by different types of ce.