  Superconductivity and ferromagnetism are two antagonistic cooperative
phenomena, which makes it difficult for them to coexist. Here we demonstrate
experimentally that they do coexist in EuFe$_{2}$(As$_{1-x}$P$_{x}$)$_{2}$ with
$0.2\leq x\leq0.4$, in which superconductivity is associated with Fe-3$d$
electrons and ferromagnetism comes from the long-range ordering of Eu-4$f$
moments via Ruderman-Kittel-Kasuya-Yosida (RKKY) interactions. The coexistence
is featured by large saturated ferromagnetic moments, high and comparable
superconducting and magnetic transition temperatures, and broad coexistence
ranges in temperature and field. We ascribe this unusual phenomenon to the
robustness of superconductivity as well as the multi-orbital characters of iron
pnictides.
