We reviewed our various results on rutheno-cuprate magneto-superconductors RuSr2GdCu2O8(Ru-1212) and RuSr2(Gd0.75Ce0.25)2Cu2O10(Ru-1222). It is observed, that it is difficult to control the oxygen content of Ru-1212, though the same is possible up to some

4. SUMMARY AND CONCLUDING REMARKS

We reviewed our various results on rutheno-cuprate magneto-superconductors RuSr2GdCu2O8-δ (Ru-1212) and RuSr2(Gd0.75Ce0.25)2Cu2O10-δ (Ru-1222). It is observed, that it is difficult to control the oxygen content of Ru-1212, though the same is possible up to some extent for Ru-1222. Samples of both phases exhibited superconductivity, presumably in the CuO2 plane at low temperatures coexisting with magnetic ordering of Ru spins of predominantly antiferromagnetic type below 140 K having a ferromagnetic component appearing below 20 K. Electrical conductivity measurements indicate that the RuO2-δ layer takes part in conduction besides the CuO2 plane. The magnetic ordering temperature of Ru spins is seen as a clear hump in the resistivity measurements, establishing the magnetic spins interaction with the conduction carriers. Though the bulk physical property measurements exhibited the magneto-superconductivity, SAED results question the same to co-existence of the two at microscopic level. Our results indicate towards the fact that solid solutions of (Ru1-xCux)-1212, which can be superconducting with x > 0.5 [24], but not magnetic may be precipitating with the stoichiometric magnetic Ru-1212 phase. Also highlighted in the review are various existing contradictions in the literature regarding physical properties of these systems. One such example is the results for Cp [16,17] that are used as the evidence of bulk superconductivity in Ru-1212. We believe the establishment of superconductivity along with low-T ferromagnetic ordering of Ru spins in intrinsically phase-pure rutheno-cuprates is yet far from conclusive.