The Magnetic Properties Of Pr-doped YBa₂Cu₃O_7-δ Single Crystals And Grain-aligned Hg_0.8Pb_0.2Ba_1.5Sr_0.5Ca₂Cu₃O_y

We investigated the procedure for growing crystals, and grew high-quality single crystals of Y_1-xPr_xBa₂Cu₃O_7-δ with x = 0.1, 0.2, 0.3, and 0.4. We measured the temperature dependence of magnetization with an external magnetic field parallel to the c-axis by using SQUID magnetometer.We studied the effects of Pr on superconductivity. We found that the superconducting transition temperature T_c decreased with x and the irreversibility lines followed the power law relation H = H₀(1-T_irr/T_c)ⁿ. The behavior of the irreversibility lines for lower x (x = 0.1 and 0.2) was similar to that of the pure YBa₂Cu₃O_7-δ with n = 1.5. However, the irreversibility lines for x = 0.3 and 0.4 were significantly suppressed with n = 2.2. This behavior was related to the enhancement of anisotropy as Pr was doped.The reversible magnetization was analyzed using a variation model proposed by Hao and Clem and the temperature dependence of the Ginzburg-Landau parameter k(T) was obtained. We found that K increased with increasing Pr concentration. From theoretical analysis, we also obtained the thermodynamic critical field H_C(T). According to the conventional theory, we deduced the various thermodynamic parameters. These parameters, such as the zero-temperature critical field H_c(0), H_c2 (0), and the upper critical field slope (dH_c2(T)/dT)Tc, decreased with x, which indicated the suppression of superconductivity from the Pr ion. The other parameters, such as the zero-temperature coherence length ξ_ab(0), and the penetration depth λ_ab(0), increased with increasing Pr concentration. The increase of λ_ab(0) could be interpreted in terms of the mixed-valence state (> 3) of the Pr ion. The hole filling in CuO₂ planes was most likely responsible for the suppression of superconductivity in the Pr doped YBCO. To our knowledge, this is the first systematic study for the physical parameters of Y_1-xPr_xBa₂Cu₃O_7-δWe also prepared the nearly single phase Hg_0.8Pb_0.2Ba_1.5Sr_0.5Ca₂Cu₃O_y samples by the simultaneous substitution of Hg by Pb and Ba by Sr in the...