Magnetically polarized Ir dopant atoms in superconducting Ba(Fe$_{1-x}$Ir$_x$)$_2$As$_2$

TL;DR

This study reveals that Ir dopant atoms in the superconductor Ba(Fe$_{1-x}$Ir$_x$)$_2$As$_2$ exhibit magnetic polarization and long-range antiferromagnetic order, coexisting with superconductivity, as shown by resonant magnetic scattering measurements.

Contribution

First direct evidence of magnetic polarization of Ir dopants in Ba(Fe$_{1-x}$Ir$_x$)$_2$As$_2$ using XRMS, demonstrating their magnetic order and coexistence with superconductivity.

Findings

Ir dopants are magnetically polarized with stripe-like antiferromagnetic order.

Magnetic order persists up to the Néel temperature of 74 K.

Magnetic order coexists microscopically with superconductivity at 5 K.

Abstract

We investigate the magnetic polarization of the Ir $5d$ dopant states in the pnictide superconductor Ba(Fe$_{1-x}$Ir$_x$)$_2$As$_2$ with $x=0.027(2)$ using Ir $L_3$ edge x-ray resonant magnetic scattering (XRMS). Despite the fact that doping partially suppresses the antiferromagnetic transition, we find that magnetic order survives around the Ir dopant sites. The Ir states are magnetically polarized with commensurate stripe-like antiferromagnetic order and long correlations lengths, $\xi_{\text{mag}}>$ 2800 and $>$850 \AA{}, in the $ab$-plane and along the c-axis, respectively, driven by their interaction with the Fe spins. This Ir magnetic order persists up to the N\'{e}el transition of the majority Fe spins at $T_N=74(2)$ K. At 5 K we find that magnetic order co-exists microscopically with superconductivity in Ba(Fe$_{1-x}$Ir$_x$)$_2$As$_2$. The energy dependence of the XRMS through the Ir $L_3$ edge shows a non-Lorentzian lineshape, which we explain in terms of interference between Ir resonant scattering and Fe non-resonant magnetic scattering.