# Anisotropic magnetic excitations and incipient N\'eel order in Ba(Fe$_{1-x}$Mn$_{x}$)$_{2}$As$_{2}$

## TL;DR

This study investigates how Mn doping in Ba(Fe$_{1-x}$Mn$_{x}$)$_{2}$As$_{2}$ affects magnetic excitations, revealing anisotropic behavior and suppression of high-temperature superconductivity due to emerging Nél order and damping of magnetic excitations.

## Contribution

It provides the first detailed RIXS analysis of magnetic excitations in Mn-doped BaFe$_2$As$_2$, showing how Mn impurities induce anisotropy and suppress superconductivity.

## Key findings

- Magnetic excitations become anisotropic with increasing Mn content.
- Emerging Nél order is evidenced by anisotropic dispersion and lineshape.
- High Mn doping suppresses magnetic excitations and likely inhibits superconductivity.

## Abstract

It is currently understood that high temperature superconductivity (SC) in the transition metal $(M)$ substituted iron arsenides Ba(Fe$_{1-x}$$M$$_{x}$)$_{2}$As$_{2}$ is promoted by magnetic excitations with wave vectors $(\pi,0)$ or $(0,\pi)$. It is known that while a small amount of Co substitution leads to SC, the same does not occur for Mn for any value of $x$. In this work, magnetic excitations in the iron arsenides Ba(Fe$_{1-x}$Mn$_{x}$)$_{2}$As$_{2}$ ($x=0.0$, $0.007$, $0.009$, $0.08$) are investigated by means of Resonant Inelastic X rays Scattering (RIXS) at the Fe $L_{3}$-edge, for momentum transfer $\boldsymbol{q}$ along the high symmetry Brillouin zone $(\pi,0)$ and $(\pi,\pi)$ directions. It is shown that with increasing Mn content ($x$), the excitations become anisotropic both in dispersion and lineshape. Both effects are detected even for small values of $x$, evidencing a cooperative phenomenon between the Mn impurities, that we ascribe to emerging N\'eel order of the Mn spins. Moreover, for $x=0.08$, the excitations along $\boldsymbol{q}\parallel(\pi,0)$ are strongly damped and nearly non dispersive. This result suggests that phases of arsenides containing local moments at the FeAs layers, as in Mn or Cr substituted phases, do not support high temperature SC due to absence of the appropriate magnetic excitations.