We have measured magnetic susceptibility of iron pnictide superconductors ${\text{SmFeAsO}}_{0.85}$ and ${\text{PrFe}}_{0.925}{\text{Co}}_{0.075}\text{AsO}$ under hydrostatic pressure up to 1.15 GPa. The superconducting transition temperature $\left(T_{\text{C}}\right)$ deceases linearly and the Meissner signal size also decreases with increasing pressure for ${\text{SmFeAsO}}_{0.85}$. In contrast, the $T_{\text{C}}$ of ${\text{PrFe}}_{0.925}{\text{Co}}_{0.075}\text{AsO}$ initially increases with pressure then saturates above $\sim 0.8\text{GPa}$. Meanwhile its Meissner signal exhibits the similar pressure dependence. Our results indicate that the pressure dependences of $T_{\text{C}}$ and superfluid density in both systems are positively correlated which suggests that these quaternary iron-based superconductors are not conventional BCS ones.

• Received 21 October 2010

DOI:https://doi.org/10.1103/PhysRevB.82.212506