SUPERCONDUCTIVITY AND MAGNETISM IN EU1-XPRXBA2CU3O7-DELTA

Measurements of the electrical resistivity rho 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 less-than-or-equal-to x less-than-or-equal-to 1 in the Eu1-xPrxBa2Cu3O7-delta system (delta almost-equal-to 0.05). The superconducting critical temperature T(c)(x) in the metallic phase (0 less-than-or-equal-to x less-than-or-similar-to x(c) almost-equal-to 0.5) was determined from the resistivity rho-(x, T), while the Neel temperature T(N)(x) in the insulating phase (x(c) less-than-or-similar-to x less-than-or-equal-to 1) was inferred from specific-heat anomalies due to antiferromagnetic (AFM) ordering of the Pr ions. The effect of "chemical" pressure on T(c)(x) in the Y1-xPrxBa2Cu3O7-delta 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 < T(N), 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+.