We performed a systematic investigation of the physical properties of CeFeAs${}_{1-x}$P${}_x$O${}_{0.95}$F${}_{0.05}$ (0 $⩽x⩽$ 1) by measuring electrical resistivity, magnetization, and specific heat. Superconductivity (SC) was observed in a wide range of P doping, $0⩽x<0.55$, with a maximum $T_c\approx 21.3$ K at $x=0.15$. Both the $x=0$ and $0.53$ samples show a reentrance behavior near the antiferromagnetic and ferromagnetic ordering temperatures of the Ce $4f$ spins, respectively. An antiferromagnetic-to-ferromagnetic (FM) evolution of Ce $4f$ electrons was observed around $x=0.45$ and SC competes with the ferromagnetic order of Ce 4$f$ electrons in this region. Our results provide clear evidence for the SC-FM competition caused by the interlayer coupling in the cerium-containing iron pnictides.

• Received 25 August 2010

DOI:https://doi.org/10.1103/PhysRevB.83.054501