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

curve shape. Also note that the MR behaviour of the present Ru-1222 sample is different from that of Ru-1212, section 3.6 (A). Ru-1212 exhibited systematic changes in sign of MR at various T and fields [10,11,17].

Figure 16 depicts the R-T plots in 0 and 7 T fields for an 100-atm O2-annealed Ru-1212 sample. The R-T behaviour in zero field is similar to that observed for the as-synthesized sample with some improvement towards metallic conductivity. Superconductivity starts with Tconset at 51 K and the TcR = 0 is seen at 43 K.

0.10

0.080.06

R [ohms]

0.040.02

0.00

50

100

150

200

250

300

T [K]

Fig.15. R-T plot and magneto-transport behaviour for an as-synthesized RuSr2(Gd0.75Ce0.25)2Cu2O10-δ sample. The inset shows the Mr behaviour of the same.

The R-T behaviour under an applied field of 7 T is nearly the same as that of 0 T above Tconset. However in 7 T field TcR = 0 is observed only around 12 K. In intermediate fields of 1 T, 3 T and 5 T, Tconset remains nearly invariant and TcR = 0 are seen at 18 K 16 K, and 14 K, respectively. Also seen is a shoulder in the R-T curve in all applied fields, the origin of which is not known. When these results of magneto-resistivity are compared with results for the as-synthesized sample (Fig. 11), one finds that TcR = 0 is nearly doubled from 23 K to 43 K after the 100-atm O2 annealing. Furthermore, TcR = 0 is observed in 7 T field also, which is not the case for the as-synthesized sample. Magneto-resistivity results for the 100-