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Nieva, G., S. Ghamaty, B. W. Lee, M. B. Maple, and I. K. Schuller. "Superconductivity and magnetism in Eu1-xPrxBa2Cu3O7-δ." Physical Review B 44 (1991): 6999.
Abstract: 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≲xc≊0.5) was determined from the resistivity ρ(x,T), while the Néel temperature TN(x) in the insulating phase (xc≲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+.
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Ghamaty, S., B. W. Lee, J. J. Neumeier, G. Nieva, and M. B. Maple. "Low-temperature specific heat of the Y1-xPrxBa2Cu3O7-δ system." Physical Review B 43 (1991): 5430.
Abstract: Low-temperature specific-heat C measurements as a function of temperature T between 0.5 and 30 K are reported for Y1-xPrxBa2Cu3O7-δ compounds with x=0, 0.2, 0.3, 0.4, 0.6, 0.8, and 1.0. The Pr contribution to the specific heat of all of the samples can be described as the sum of a Pr nuclear Schottky anomaly of the form CN(T)=AT-2, a linear term CL(T)=γT, and a Pr magnetic anomaly. For compounds with x≤0.6, which are metallic and superconducting, the Pr magnetic specific-heat anomaly has the same temperature dependence as a Kondo anomaly. For the compounds with x≥0.8, which are insulating, the magnetic specific-heat anomaly is consistent with antiferromagnetic ordering of the Pr ions with Néel temperatures TN of 10.9 and 15.7 K for x=0.8 and 1.0, respectively. For T<TN, the antiferromagnetic specific-heat anomaly has the form CM(T)=MT3, characteristic of three-dimensional antiferromagnetic magnons.
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Maple, M. B., N. Y. Ayoub, J. Beille, T. Bjornholm, Y. Dalichaouch, E. A. Early, S. Ghamaty, B. W. Lee, J. T. Markert, J. J. Neumeier et al. "Experiments on Electron-and Hole-Doped High Tc Copper Oxide Superconductors." Transport Properties of Superconductors (1990): 536.
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