Ferromagnetic correlations and mixed Ru valence in the magnetic superconductor RuSr2(Eu,Gd)Cu2O8

A. Butera; A. Fainstein; E. Winkler; J. Tallon

doi:10.1103/PhysRevB.63.054442

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Ferromagnetic correlations and mixed Ru valence in the magnetic superconductor RuSr2(Eu,Gd)Cu2O8

A. Butera, A. Fainstein, E. Winkler, J. Tallon

DOI 10.1103/PhysRevB.63.054442 · Physical Review B

T1

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Abstract

We present a characterization through magnetization measurements as a function of field and temperature of the magnetic superconductor RuSr2RCu2O8 (R=Eu or Gd). The effective magnetic moment was carefully determined from measurements up to 900 K. For both compounds we have obtained almost the same value, μeff∼3.15(4)μβ. This value confirms recent x-ray absorption experiments where a mixed valence state (40%Ru4+–60%Ru5+) was proposed. We have found that the predominant interaction among Ru ions is ferromagnetic [Θ=100(3) K and Θ=87(3) K for the Eu and Gd compounds, respectively], but the high-field susceptibility curve displays the characteristics of an antiferromagnetic transition. The possible type of order of the Ru moments is discussed in view of these and previous experiments. We propose a type-I ordering (antiferromagnetically coupled ferromagnetic RuO2 planes) and give reasons supporting this choice.

Source-reported materials — not catalogue approval

Formula	Reported Tc (K)	Pressure (GPa)	Type
RuSr2GdCu2O8 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	48	Pressure not reported	unknown
RuSr2EuCu2O8 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	33	Pressure not reported	unknown