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

moment appears to occur above say 5 Tesla applied fields, not seen in the present figure. The contribution from the ferromagnetic component starts to appear below 100 K.

The presence of the ferromagnetic component is confirmed by a hysteresis loop measured at 5 K in the M-H plot, see inset in Fig. 11. To compare the M-H results for Ru-1222 with those for Ru-1212, we showed the same for Ru-1212 in lower inset of Fig. 9. The opening of the M-H loop for Ru-1212 is seen in magnetic fields up to 4000 Oe, which is larger in comparison to the 1,000 Oe observed for Ru-1222.

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M [emu]

-1

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-6

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µ0H [T]

Fig. 11. M-H behaviour for an as-synthesized RuSr2(Gd0.75Ce0.25)2Cu2O10-δ sample. The inset shows

the low field M-H hysteresis for the same.

Figure 12 shows the χ-T behaviour in the temperature range of 5 to 150 K for the 100-atm O2-annealed sample under applied field of 5 Oe, measured in both ZFC and FC modes. The ZFC and FC curves start branching at around 120 K with a sharp upward turn at 85 K. The ZFC branch shows further a cusp at round 65 K and a diamagnetic transition around 40 K. Also seen is a dip in FC part of magnetization at 40 K, i.e, the same temperature where superconductivity sets in. This indicates towards bulk nature of superconductivity in the 100-atm O2-annealed sample.

Interestingly when compared with the as-synthesized sample, one finds that for 100-atm O2-annealed sample while the superconductivity is enhanced, the magnetic ordering (ZFC-FC branching and cusp) temperatures are decreased. Also, the dip in FC magnetization is not seen for the as-synthesized sample. This indicates the competing nature of magnetism and superconductivity in Ru-1222. Weak ferromagnetic component is seen in the 100-atm