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

The obtained result suggests that the valence of Ru in Ru-1222 is affected by the change in oxygen content. It is therefore interesting to compare the presently obtained Ru valence values to that previously reported for a RuSr2(Gd0.7Ce0.3)2Cu2O10-δ sample (+4.95) with Tc ≈ 60 K [31]. For the three Ru-1222 samples the Ru valence/Tc values thus were: +4.74/30 K, +4.81/43 K and +4.95/60 K. (Note that the XANES measurements and analyses were carried out in parallel ways for all the three samples.) The latter two samples were both annealed under 100 atm oxygen pressure, but with different temperature programs. It is thus likely that the one previously reported [31] had somewhat higher oxygen content than the present 100-atm O2-annealed sample. It seems that the valence of Ru in Ru-1222 depends on the oxygen content, thus indirectly suggesting that the changes in oxygen stoichiometry occur in the RuO2-δ layer. Here it is interesting to note that a previous study had shown that Ru remains essentially unchanged (close to pentavalent) upon varying the Ce-substitution level within 0.3 ≤ x ≤ 0.5 in fully oxygen-loaded RuSr2(Gd1-xCex)2Cu2O10-δ samples [31].

283.6 283.8 284.0 284.2 284.4 284.6 284.8 285.0

Energy (eV)

Fig. 4. Ru LIII-edge XANES spectra for reference materials, Sr2RuO4 (RuIV) and Sr2GdRuO6 (RuV),

and for as-synthesized and 100-atm O2-annealed RuSr2(Gd0.75Ce0.25)2Cu2O10-δ samples.

Ru LIII-edge XANES analysis for an as-synthesized (final annealing in O2 at 1075 oC) RuSr2GdCu2O8-δ sample revealed a valence value of +4.62 [28]. This value is very close to that reported in Ref. [30] for a RuSr2GdCu2O8-δ sample, i.e. +4.60, with the final annealing performed in O2 at 1060 oC.

Normalized Absorption