Abstract
Crystal structure, superconductivity, and magnetic order of the Pr spins in polycrystalline (Pr 0.55 Nd 0.45 )Ba 2 Cu 3 O 7 were studied by x ray and ac susceptibility measurements. The crystal structure was determined by applying the Rietveld refinement method to the high resolution x-ray diffraction pattern. The Pr and Nd atoms are randomly mixed to form (Pr 0.55 Nd 0.45 ) layers rather than two separated PrBa 2 Cu 3 O 7 and NdBa 2 Cu 3 O 7 phases. Above 50 K the temperature dependence of the in-phase component of the ac susceptibility χ′(T) exhibits Curie-Weiss behavior. Below 50 K diamagnetic responses become evident, indicating the onset of superconductivity. A dc field of strength 2 kOe smears out 80% of the diamagnetic signals, showing the superconducting pairings are being destroyed by the applied field. Further reducing the temperature, χ′(T) shows an upturn at T ≈ 15 K below which χ′(T) increases rapidly with decreasing temperature, presumably due to the Pr spin ordering. Both me onset of superconductivity and the spin ordering of the Pr ions are also evident in the temperature dependence of the out-of-phase component of the ac susceptibility χ″(T). © 1997 American Institute of Physics.