X-ray photoelectron spectroscopy of superconducting RuSr₂Eu_1.5Ce_0.5Cu₂O₁₀ and nonsuperconducting RuSr₂EuCeCu₂O₁₀

Abstract

We report x-ray photoelectron spectroscopic investigation of RuSr₂Eu_1.5Ce_0.5Cu₂O₁₀ with ferromagnetic T_C~100 K and a superconducting transition temperature of ~30 K compared with RuSr₂EuCeCu₂O₁₀, which is a ferromagnetic (T_C~150 K) insulator. Our results show that the rare earths, Eu and Ce, are in 3+ and 4+ states, respectively. Comparing the Ru core level spectra from these compounds to those from two Ru reference oxides, we also show that Ru in these ruthenocuprates is always in 5+ state, suggesting that the doped holes in the superconducting compound arising from the substitution of Ce⁴⁺ by Eu³⁺ are primarily in the Cu-O plane, in close analogy to all other doped high-T_Ccuprates. Analysis of Cu 2p spectra in terms of a configuration interaction model provides a quantitative description of the gross electronic structures of these ruthenocuprates.