The layered compound CaClFeP is an Arsenic-free high T_c iron-pnictide

We first analyze why the iron pnictides with high $T_c$ superconductivity so far are As-based, by the Hund's rule correlation picture, then examine the P-based and Sb-based cases, respectively. Consequently, we propose that CaClFeP with ZrCuSiAs-type structure is an As-free high $T_c$ iron-pnictide. The subsequent density functional theory calculations show that the ground state of CaClFeP is of a collinearly antiferromagnetic order on Fe moments with structural distortion, resulting from the interplay between the strong nearest and next-nearest neighbor antiferromagnetic superexchange interactions bridged by P atoms, similar as the As-based pnictides. The other P-based pnictides are either nonmagnetic or magnetic but with weak exchange interactions. The Sb-based pnictides unlikely show high $T_c$ superconductivity because of the existence of robust ferromagnetic order.