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

MPMS-5S). Resistivity measurements under an applied magnetic field of 0 - 7 T were performed in the temperature range of 5 - 300 K using a physical-property-measurement system (Quantum Design: PPMS). Electron diffraction (ED) patterns were obtained using a transmission electron microscope (TEM; Hitachi H-9000) operated at an accelerating voltage of 300 kV. The Ru LIII-edge XANES measurements were performed at room temperature for polycrystalline samples at the BL15B beamline of the Synchrotron Radiation Research Center (SRRC) in Hsinchu, Taiwan.

3. RESULTS & DISCUSSION

3.1 Phase formation and lattice parameters: X-ray diffraction results

The presently studied RuSr2GdCu2O8-δ samples possess a tetragonal Ru-1212 structure with a space group P4/mmm. For an as-synthesized sample lattice parameters were determined at a = b = 3.8218(6) Å and c = 11.476(1) Å. Corresponding X-ray diffraction pattern is shown in Fig. 1. Small amount of SrRuO3 is also seen, which is marked on the pattern.

(103)

RuSr2GdCu2O8-δ

space group: P4/mmm

Relative Intensity

* : SrRuO3

(213)

(200)

(101)

(104)

(115)

(211)

(113)

(105)

(102)

(204)

(100)

(107)

(205)

(117)

206)

203040502 θ (deg.)

6070

(207)

(109)

80

Fig. 1. X-ray diffraction pattern for an as-synthesized RuSr2GdCu2O8-δ sample.

Essentially no difference was found in X-ray diffraction pattern or lattice parameters for the 100-atm O2-annealed sample, suggesting that the oxygen content remained unchanged upon the high-O2-pressure annealing. Worth mentioning is the fact that earlier one of us obtained a phase-pure (no trace of SrRuO3 within the XRD detection limit) Ru-1212