Superconductivity and magnetism in Eu1-xPrxBa2Cu3O7-δ

Measurements of the electrical resistivity ρ as a function of temperature T, and low-temperature specific heat C as a function of T and magnetic field H, have been performed for Pr concentrations 0≤x≤1 in the Eu1-xPrxBa2Cu3O7-δ system (δ∼0.05). The superconducting critical temperature Tc(x) in the metallic phase (0≤x approx-lt xc∼0.5) was determined from the resistivity ρ(x,T), while the Neel temperature TN(x) in the insulating phase (xc approx-lt x≤1) was inferred from specific-heat anomalies due to antiferromagnetic (AFM) ordering of the Pr ions. The effect of ''chemical'' pressure on Tc(x) in the Y1-xPrxBa2Cu3O7-δ system is opposite to that of applied hydrostatic pressure. The Pr contributions to the specific heat in the insulating phase have the form C(T)=MT3 for T<TN, characteristic of three-dimensional AFM magnons. In contrast, the Pr contribution to C(T) in the metallic phase takes the form of a broad anomaly that can be described by a spin-1/2 Kondo model. The entropy associated with the Pr specific-heat anomalies in both the metallic and insulating phases is close to R ln2, indicative of a doublet ground state for Pr in the crystalline electric field and a Pr valence close to 4+