The Ru valence in the antiferromagnetic and ferromagnetic ruthenocuprate superconductors ${\mathrm{RuSr}}_{2}R{\mathrm{Cu}}_2{\mathrm{O}}_8$ (Ru-1212), with $R=\mathrm{Eu},$ Gd, and ${\mathrm{Gd}}_{0.6}{\mathrm{Dy}}_{0.4},$ has been studied using Ru $L_{\mathrm{III}}$-edge x-ray absorption near-edge structure spectroscopy. Comparison with reference materials ${\mathrm{Sr}}_2{\mathrm{RuO}}_4$ and ${\mathrm{Sr}}_2{\mathrm{RuGdO}}_6$ in which Ru is tetravalent and pentavalent, respectively, reveals the strong likelihood of mixed valence in Ru-1212 with 40–50% ${\mathrm{Ru}}^{4+}$ and 60–50% ${\mathrm{Ru}}^{5+},$ depending upon specific substitutions. This introduces several possibilities for the nature of the magnetic ordering in these compounds.

• Received 24 May 2000

DOI:https://doi.org/10.1103/PhysRevB.63.212507