The onset of magnetism peaked around x=1/4 in optimally electron-doped LnFe(1-x)Ru(x)AsO(1-y)F(y) (Ln = La, Nd or Sm) superconductors

TL;DR

This study reveals that static magnetism in optimally electron-doped LnFe(1-x)Ru(x)AsO(1-y)F(y) superconductors peaks around x=1/4, coexists with superconductivity, and influences the phase diagram and transition temperatures.

Contribution

It demonstrates the dome-shaped dependence of magnetic order on Ru substitution and its correlation with structural parameters and superconducting properties.

Findings

Magnetism peaks at x=1/4 in Ru-doped samples.

Magnetic ordering temperature T_N shows a dome-like dependence on x.

Superconductivity is suppressed as static magnetism develops, disappearing at x=0.6.

Abstract

The appearance of static magnetism, nanoscopically coexisting with superconductivity, is shown to be a general feature of optimally electron-doped LnFe(1-x)Ru(x)AsO(1-y)F(y) superconductor (Ln - lanthanide ion) upon isovalent substitution of Fe by Ru. The magnetic ordering temperature T_N and the magnitude of the internal field display a dome-like dependence on x, peaked around x=1/4, with higher T_N values for those materials characterized by a larger z cell coordinate of As. Remarkably, the latter are also those with the highest superconducting transition temperature (T_c) for x=0. The reduction of T_c(x) is found to be significant in the x region of the phase diagram where the static magnetism develops. Upon increasing the Ru content superconductivity eventually disappears, but only at x=0.6.