A high-quality PrFeAsO$_{ 1-\delta}$ single crystal ($T_{ \rm c}=44$ K) has been investigated by the magnetic torque. Antiferromagnetism of the Pr$^{ 3+}$ ions was found to coexist with superconductivity in PrFeAsO$_{ 1-\delta}$ at temperatures below $T_\mathrm{ N}=14$ K. We predict a magnetic structure that is not in accordance with earlier neutron studies performed using polycrystalline nonsuperconducting specimens. As the temperature decreases, the superconducting anisotropy $\gamma\sim 4$ of PrFeAsO$_{ 1-\delta}$ increases near $T_c$ and tends to decrease slightly at lower temperatures.
Categories: cond-mat.supr-con