Magnetic-superconducting phase diagram of Eu2−xCexRuSr2Cu2O10−δ

Abstract

Eu2−xCexRuSr2Cu2O10−δ (Ru-2122) is the first Cu-O-based system in which superconductivity (SC) in the CuO2 planes and weak ferromagnetism (WFM) in the Ru sublattice coexist. The hole doping in the CuO2 planes is controlled by appropriate variation of the Ce concentration. SC occurs for Ce contents of 0.4–0.8, with the highest TC=35K for Ce=0.6. The as-prepared non-SC EuCeRuSr2Cu2O10 (x=1) sample exhibits magnetic irreversibility below Tirr=125K and orders antiferromagnetically (AFM) at TM=165K. The saturation moment at 5 K is Msat=0.89μB/Ru close to the expected 1μB for the low-spin state of Ru5+. Annealing under oxygen pressures does not affect these parameters, whereas depletion of oxygen shifts both Tirr and TM up to 169 and 215 K, respectively. Systematic magnetic studies of Eu2−xCexRuSr2Cu2O10−δ show that TM, Tirr, and Msat decrease with x, and the full Ce-dependent magnetic-SC phase diagram is presented. A simple model for the SC state is proposed. We interpret the magnetic behavior in the framework of our ac and dc magnetic studies, and argue that (i) the system becomes AFM ordered at TM; (b) at Tirr<TM, WFM is induced by the canting of the Ru moments: and (c) at lower temperatures, the appropriate samples become SC at TC. The magnetic features are not affected by the SC state, and the two states coexist.

Source-reported materials — not catalogue approval

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