摘要
The Ru valence in the antiferromagnetic and ferromagnetic ruthenocuprate superconductors RuSr 2 RCu 2 O 8 (Ru-1212), with R=Eu, Gd, and Gd 0.6 Dy 0.4 , has been studied using Ru L III -edge x-ray absorption near-edge structure spectroscopy. Comparison with reference materials Sr 2 RuO 4 and S r 2RuGdO 6 in which Ru is tetravalent and pentavalent, respectively, reveals the strong likelihood of mixed valence in Ru-1212 with 40-50% Ru 4+ and 60-50% Ru 5+ , depending upon specific substitutions. This introduces several possibilities for the nature of the magnetic ordering in these compounds.