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

may be utilized in precise oxygen content determination for these phases. It was found that the two Ru-1212 samples, as-synthesized and 100-atm O2-annealed, possess nearly the same oxygen content. For the Ru-1222 phase, several repeated experiments revealed that the difference in oxygen content between the as-synthesized and the 100-atm O2-annealed samples is ～0.15 oxygen atoms per formula unit [28,29]. In terms of the oxygen-content variation, the TG results thus are consistent with the conclusions made based on the XRD data.

100

Relative Mass (%)

9896949290

Temperature (C)

Fig. 3. TG curves for as-synthesized RuSr2GdCu2O8-δ and RuSr2(Gd0.75Ce0.25)2Cu2O10-δ samples

recorded in 5 % H2/95 % Ar atmosphere.

3.3 Valence of Ru: XANES spectroscopy results

The Ru LIII-edge XANES spectra obtained for an as-synthesized and a 100-atm O2-annealed Ru-1222 sample are displayed in Fig. 4. The spectra were analyzed quantitatively by fitting them to certain linear combinations of those for reference materials Sr2RuO4 (RuIV) and Sr2GdRuO6 (RuV). All the spectra exhibited two peaks, the higher-energy one and the lower-energy one being due to 2p → eg and 2p → t2g transitions, respectively [30-32]: with increasing Ru valence from +IV to +V, the crystal-field splitting increases and thereby the separation between the two peaks enhances. Furthermore, the peaks are accordingly shifted by ～1.5 eV to the higher energy. From Fig. 4, both the Ru-1222 samples are between the two reference materials in terms of the Ru valence. Fitting the spectra revealed a valence value of +4.74 for the as-synthesized sample and +4.81 for the 100-atm O2-annealed sample [29].