Fast recovery of the stripe magnetic order by Mn/Fe substitution in F-doped LaFeAsO superconductors

TL;DR

This study demonstrates that minimal Mn substitution in F-doped LaFeAsO superconductors rapidly suppresses superconductivity and restores magnetic order, revealing the material's proximity to an electronic instability.

Contribution

The paper provides experimental and theoretical evidence that Mn doping induces magnetic order and charge localization, highlighting the strongly correlated nature of F-doped LaFeAsO.

Findings

0.5% Mn doping suppresses superconductivity

Mn doping restores magnetic and structural order

Charge localization occurs in the system

Abstract

$^{75}$As Nuclear Magnetic (NMR) and Quadrupolar (NQR) Resonance were used, together with M\"{o}ssbauer spectroscopy, to investigate the magnetic state induced by Mn for Fe substitutions in F-doped LaFe$_{1-x}$Mn$_{x}$AsO superconductors. The results show that $0.5$% of Mn doping is enough to suppress the superconducting transition temperature $T_c$ from 27 K to zero and to recover the magnetic structure observed in the parent undoped LaFeAsO. Also the tetragonal to orthorhombic transition of the parent compound is recovered by introducing Mn, as evidenced by a sharp drop of the NQR frequency. The NQR spectra also show that a charge localization process is at play in the system. Theoretical calculations using a realistic five-band model show that correlation-enhanced RKKY exchange interactions between nearby Mn ions stabilize the observed magnetic order, dominated by $Q_1=(\pi,0)$ and $Q_2=(0,\pi)$ ordering vectors. These results give compelling evidence that F-doped LaFeAsO is a strongly correlated electron system at the verge of an electronic instability.