Coexistence of ferromagnetism and superconductivity in the hybrid ruthenate-cuprate compound ${\mathrm{RuSr}}_2{\mathrm{GdCu}}_2{\mathrm{O}}_8$ studied by muon spin rotation and dc magnetization

We have investigated the magnetic and the superconducting properties of the hybrid ruthenate-cuprate compound ${\mathrm{RuSr}}_2{\mathrm{GdCu}}_2{\mathrm{O}}_8$ by means of zero-field muon-spin rotation (ZF-μSR) and dc magnetization measurements. The dc-magnetization data established that this material exhibits ferromagnetic order of the Ru moments [μ(Ru)≈1 ${\mu }_B]$ below $T_C=133\mathrm{}$ K and becomes superconducting at a much lower temperature $T_c=16\mathrm{}$ K. The ZF-μSR experiments indicate that the ferromagnetic phase is homogeneous on a microscopic scale and accounts for most of the sample volume. They also suggest that the magnetic order is not significantly modified at the onset of superconductivity.