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

1212, the Tconset under a magnetic field decreased like the present case [10,11,14,17,25]. The present behaviour of transition broadening under a magnetic field is presumably due to formation of SNS/SIS junctions/clusters in the present and similar samples. Non-superconducting RuSr2GdCu2O8-δ might be stacked between superconducting Ru1-, resulting in ideal SIS or SNS junctions within the material. xCuxSr2GdCu2O8-δ

0.16

0.12R [ohms]

0.080.040.00

T [K]

Fig. 13. R-T plot and magneto-transport behaviour for an as-synthesized (superconducting)

RuSr2GdCu2O8-δ sample.

Inset of Fig. 13 shows the magnetoresistance (MR) behaviour of the present Ru-1212 sample at various fields and temperatures. MR is negative in all applied fields upto 7 T above the magnetic ordering temperature, i.e. at 150 K and 200 K. Maximum negative MR of up to 2 % is observed at 150 K, which is close to the magnetic ordering temperature of around 140 K. At temperatures below the ordering temperature (100 K and 50 K), MR displays a positive peak at low fields and becomes negative at higher fields. This behaviour is in general agreement with previous reports [10,11,17].