Doping evoluton of antiferromagnetic order and structural distortion in LaFeAsO$_{1-x}$F$_x$

TL;DR

This study investigates how fluorine doping affects the structural and magnetic properties of LaFeAsO, revealing that doping suppresses antiferromagnetic order before superconductivity appears, indicating a competitive relationship.

Contribution

It provides detailed neutron scattering data showing the evolution of structural distortion and AFM order with fluorine doping in LaFeAsO.

Findings

Doping reduces the structural distortion temperature.

Long-range AFM order is suppressed before superconductivity emerges.

Superconductivity coexists with either tetragonal or orthorhombic structures.

Abstract

We use neutron scattering to study the structural distortion and antiferromagnetic (AFM) order in LaFeAsO$_{1-x}$F$_{x}$ as the system is doped with fluorine (F) to induce superconductivity. In the undoped state, LaFeAsO exhibits a structural distortion, changing the symmetry from tetragonal (space group $P4/nmm$) to orthorhombic (space group $Cmma$) at 155 K, and then followed by an AFM order at 137 K. Doping the system with F gradually decreases the structural distortion temperature, but suppresses the long range AFM order before the emergence of superconductivity. Therefore, while superconductivity in these Fe oxypnictides can survive in either the tetragonal or the orthorhombic crystal structure, it competes directly with static AFM order.