A ferromagnetic quantum critical point in heavy-fermion iron oxypnictide CeFe_1-xCr_xPO

We report crystallographic and magnetic properties of layered iron oxypnictide CeFe_1-xCr_xPO (x = 0.000-0.692). Interlayer distances between Ce₂O₂ and (Fe_1-xCr_x)₂P₂ layers increase as a function of x, suggesting suppression of Kondo coupling among hybridized conducting orbitals and localized Ce 4f orbitals. CeFe_1-xCr_xPO (x = 0.100-0.384) exhibits finite ferromagnetic transition temperatures (Tcurie) obtained by Arrott plots, although ⁵⁷Fe Mössbauer spectra reveal paramagnetic Fe sublattice at T 4.2 K. These results indicate that the ferromagnetic phase transitions of samples are mainly due to Ce sublattice. For the samples with x ≥ 0.500, no ferromagnetic order is observed down to 2 K. These results verify that ferromagnetic quantum critical points of CeFe_1-xCr_xPO appear at 0.045 ≤ x ≤ 0.100 and 0.384 ≤ x ≤ 0.500.