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

3.5 Magneto-superconductivity and magnetic characteristics: SQUID results

A. Non-superconducting Ru-1212 samples

Figure 8 depicts both ZFC (zero-field-cooled) and FC (field-cooled) magnetic moment (M) versus temperature (T) plots for various RuSr2GdCu2O8-δ samples with an applied field of 10 Oe [27]. As is seen from this figure the ZFC and FC magnetisation curves show a significant branching around 145 K for the as-synthesized sample with a further sharp drop in magnetisation around 2.6 K.

The branching of ZFC and FC curves at 145 K originates from the magnetic ordering of Ru moments and the sharp peak at 2.6 K is due to antiferromagnetic ordering of Gd moments. Interestingly in presently studied non-superconducting RuSr2GdCu2O8-δ samples the ordering temperature of Ru moments appears to be 13 K higher than the value reported for similar but superconducting samples [1,6,8]. Both the ZFC and FC branching about 145 K and the sharp peak at 2.6 K are seen for all the samples including the high-O2-pressure annealed and the argon annealed ones. None of the samples show any traces of superconductivity down to 2 K, even with very low field measurements at 1.5 Oe. Worth reminding is the fact that these samples of ours contain no traces of SrRuO3. These non-superconducting RuSr2GdCu2O8-δ samples showed a similar ferromagnetic component at 5 K, as for reported superconducting samples.

0.015

M [emu]

0.010

0.005

0.000

T [K]

Fig. 8. M-T plots for various non-superconducting RuSr2GdCu2O8-δ samples.