Superconductivity induced by phosphorus doping and its coexistence with   ferromagnetism in EuFe$_{2}$(As$_{0.7}$P$_{0.3}$)$_{2}$
  We have studied EuFe$_{2}$(As$_{0.7}$P$_{0.3}$)$_{2}$ by the measurements of x-ray diffraction, electrical resistivity, thermopower, magnetic susceptibility, magnetoresistance and specific heat. Partial substitution of As with P results in the shrinkage of lattice, which generates chemical pressure to the system. It is found that EuFe$_{2}$(As$_{0.7}$P$_{0.3}$)$_{2}$ undergoes a superconducting transition at 26 K, followed by ferromagnetic ordering of Eu$^{2+}$ moments at 20 K. This finding is the first observation of superconductivity stabilized by internal chemical pressure, and supplies a rare example showing coexistence of superconductivity and ferromagnetism in the ferro-arsenide family. 
Zhi Ren, Qian Tao, Shuai Jiang, Chunmu Feng, Cao Wang, Jianhui Dai,   Guanghan Cao and Zhu'an Xu