Magnetic ordering and superconductivity in the Nd_1−xPr_xBa₂Cu₃O_7−y system

Abstract

We have investigated magnetic ordering and superconducting properties of the Nd_1−xPr_xBa₂Cu₃O_7−y series (x=0-1.0). The system is superconducting in the 0≤x≤0.25 range, beyond which the superconductivity is quenched. The value of x_cr is estimated to be ≈0.27. For x≥0.3, electrical resistivity displays insulator-like behavior. Heat capacity measurements (2-25 K temperature range) on this series reveal that the peak in the C_p(T) data at about 16.5 K for x=1.0 (identified as the Néel temperature, T_N, due to the Pr ion ordering) moves to lower temperatures, and is progressively suppressed as x decreases from x=1.0 to x=0.4 (insulating regime). The T_N(x) curve is linear and lies above the corresponding plots for Y_1−xPr_xBa₂Cu₃O_7−y and Eu_1−xPr_xBa₂Cu₃O_7−y. We point out that T_N(x) depends linearly on R³⁺ ionic radius, similar to that reported in the literature for T_c(x). For x=0.6, 0.4, a broad anomaly in C_p(T) develops around 3 K. For x=0.2 (superconducting sample), the peak in C_p(T), due to the Pr ion ordering, is not observed, as expected; however, below 5 K, C_p exhibits a large upturn which seems to develop into a maximum at about 2 K. This feature at about 2-3 K in C_p(T) may be due to a Schottky anomaly due to the Nd ions.