Phase separation in superconducting EuBa2Cu3O6+x

We report a μSR study of four EuBa2Cu3O6+x samples prepared with different oxygen stoichiometry (x=0.25-0.5) and annealing temperatures. In all the samples except the least-doped one, the high-TN antiferromagnetic phase was found to coexist with a sizable non-magnetic fraction which, in the x≥0.38 samples annealed at a higher temperature, develops superconductivity with a surprisingly high Tc=93 K. Complementary Cu-NQR investigation rules out trivial chemical inhomogeneities as the origin of the phase-separated state, and rather points to intrinsic phase separation mechanisms, such as stripe-phase instabilities