Superconductivity and Glassiness in Strongly Underdoped Y$_{1-x}$Pr$_{x}$Ba$_2$Cu$_3$O$_{7-\delta}$

We performed magnetic investigations on single crystals of Y$_{0.47}$Pr$_{0.53}$Ba$_2$Cu$_3$O$_{7-\delta}$ ($T_{c}=7.0$ K) at temperatures $46.3$ K exhibit an evolution from a hysteretic loop ty pical for superconducting mixed state at low $H$ to one typical for a spin glass state at high $H$. The latter opens as a separate loop above the irreversible field and expands on the account of the superconducting loop with which overlaps at $T>T_{c}$.