Magnetic ground state of superconducting Eu(Fe0.88Ir0.12)2As2: A combined neutron diffraction and first-principles calculation study

TL;DR

This study combines neutron diffraction and first-principles calculations to reveal that Eu(Fe$_{0.88}$Ir$_{0.12}$)$_{2}$As$_{2}$ exhibits ferromagnetic Eu$^{2+}$ order along the c-axis below 17 K, with suppressed SDW and developed superconductivity.

Contribution

It provides the first detailed experimental and theoretical analysis of the magnetic ground state in Ir-doped EuFe$_{2}$As$_{2}$, showing ferromagnetic Eu$^{2+}$ order and its relation to superconductivity.

Findings

Eu$^{2+}$ spins are ferromagnetically aligned along c-axis below 17 K.

No structural phase transition detected within experimental uncertainty.

Ir substitution enhances hybridization and bandwidth, favoring superconductivity.

Abstract

The magnetic order of the localized Eu$^{2+}$ spins in optimally-doped Eu(Fe$_{1-x}$Ir$_{x}$)$_{2}$As$_{2}$ ($\mathit{x}$ = 0.12) with superconducting transition temperature $\mathit{T_{SC}}$ = 22 K was investigated by single-crystal neutron diffraction. The Eu$^{2+}$ moments were found to be ferromagnetically aligned along the $\mathit{c}$-direction with an ordered moment of 7.0(1) $\mu_{B}$ well below the magnetic phase transition temperature $\mathit{T_{C}}$ = 17 K. No evidence of the tetragonal-to-orthorhombic structural phase transition was found in this compound within the experimental uncertainty, in which the spin-density-wave (SDW) order of the Fe sublattice is supposed to be completely suppressed and the superconductivity gets fully developed. The ferromagnetic groud state of the Eu$^{2+}$ spins in Eu(Fe$_{0.88}$Ir$_{0.12}$)$_{2}$As$_{2}$ was supported by the first-principles density functional calculation. In addition, comparison of the electronic structure calculations between Eu(Fe$_{0.875}$Ir$_{0.125}$)$_{2}$As$_{2}$ and the parent compound EuFe$_{2}$As$_{2}$ indicates stronger hybridization and more expanded bandwith due to the Ir substitution, which together with the introduction of electrons might work against the Fe-SDW in favor of the superconductivity.