Coexistence of ferromagnetism and superconductivity in the hybrid ruthenate-cuprate compound RuSr 2 GdCu 2 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-\ensuremath{\mu}SR) and dc magnetization measurements. The dc-magnetization data established that this material exhibits ferromagnetic order of the Ru moments [\ensuremath{\mu}(Ru)\ensuremath{\approx}1 ${\ensuremath{\mu}}_{B}]$ below ${T}_{C}=133$ K and becomes superconducting at a much lower temperature ${T}_{c}=16$ K. The ZF-\ensuremath{\mu}SR 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.