Enhancement of flux pinning by Pr doping in ${\mathrm{Y}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Pr}}_{\mathit{x}}$${\mathrm{Ba}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ (0≤x≤0.4)

Magnetic relaxation measurements in a magnetic field of 5 kOe at temperatures 5 K ≤T≤90 K have been made on the system ${\mathrm{Y}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Pr}}_{\mathit{x}}$ ${\mathrm{Ba}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ for 0≤x≤0.4. The measurements reveal two peaks in the normalized logarithmic decay of the magnetization S as a function of temperature for the full range of Pr concentrations studied. The occurrence of the second peak in S could be a reflection of the softening of the flux lattice on approaching the melting line. Both the pinning energy at 27 K and the intragranular critical current density at 10 K exhibit maxima at x≊0.1–0.2, with values that are about twice the corresponding values at x=0.