Phase Separation and Finite Size Scaling ${\mathrm{inLa}}_{2\mathrm{-}\mathrm{x}}$${\mathrm{Sr}}_{\mathrm{x}}$${\mathrm{CuO}}_{4+\mathrm{\delta }}$[0⩽(x,γ)⩽0.03]

A study of the phase diagram and magnetic susceptibility χ(x,δ,T) of the title system is reported. For δ≃0.03, macroscopic phase separation, below ≃300 K into ${\mathrm{superconductingLa}}_{2\mathrm{-}\mathrm{x}}$ ${\mathrm{Sr}}_{\mathrm{x}}$ ${\mathrm{CuO}}_{4+\mathrm{\delta }}$(δ≃0.08) and ${\mathrm{nonsuperconductingLa}}_{2\mathrm{-}\mathrm{x}}$ ${\mathrm{Sr}}_{\mathrm{x}}$ ${\mathrm{CuO}}_{4+{\mathrm{\delta }}^{\mathrm{″}}}$(δ″≃0.00) phases, known to occur forx=0, disappears by x≃0.03. The behaviors of the Néel temperature ${\mathrm{T}}_{\mathrm{N}}$(x) and χ(x,T) of the antiferromagnetic phase (0≃x≲0.02,δ″≃0.00) reveal a novel microscopic segregation of the doped holes in this phase into walls of hole-rich material separating undoped domains. © 1993 The American Physical Society