mu SR studies of superconductivity in eutectically grown mixed ruthenates

The low-temperature magnetic behavior of the double-layered ruthenate Sr3Ru2O7, as grown from a eutectic Sr2RuO4-Sr3Ru2O7 system, was investigated via zero- and transverse-field muon-spin rotation. The gradual increase of the muon relaxation rate observed below 2.5 K, even in the absence of applied magnetic fields, indicates the occurrence of a spontaneous breaking of time-reversal symmetry. The onset of the latter at a temperature above 1.5 K, the Tc of the single phase Sr2RuO4, provides evidence about an unconventional superconducting state in the eutectic phase, which most likely takes place at the interface between the Sr2RuO4 and Sr3Ru2O7 domains, or even inside the Sr3Ru2O7 phase. We show that the superconducting state manifests a two-component behavior in the transverse-field response with change-over at about T=2.5 K and T=1.5 K. The comparison with zero-field ?SR data in the Ru-Sr2RuO4 eutectic system rules out the possibility of spurious effects due to embedded Ru islands.