  We report a systematic study on the influence of antiferromagnetic and
ferromagnetic phases of Eu^2+ moments on the superconducting phase upon doping
the As site by isovalent P, which acts as chemical pressure on EuFe_2As_2. Bulk
superconductivity with transition temperatures of 22 K and 28 K are observed
for x=0.16 and 0.20 samples respectively. The Eu ions order
antiferromagnetically for x<=0.13, while a crossover is observed for x>=0.22
whereupon the Eu ions order ferromagnetically. Density functional theory based
calculations reproduce the observed experimental findings consistently. We
discuss in detail the coexistence of superconductivity and magnetism in a tiny
region of the phase space and comment on the competition of ferromagnetism and
superconductivity in the title compound.
