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

atm O2-annealed Ru-1212 sample substantiate the magnetization results, indicating that superconductivity is enhanced upon the 100-atm O2 annealing. The 100-atm O2-annealed Ru-1222 sample revealed a small negative MR effect (inset in Fig. 16) in the whole temperature range similar to that as for the as-synthesized sample.

0.08

R (Ohms)

0.060.040.020.00

T [K]

Fig.16. R-T plot and magneto-transport behaviour for a 100-atm O2-annealed

RuSr2(Gd0.75Ce0.25)2Cu2O10-δ sample. The inset shows the MR behaviour of the same.