Crystal and magnetic structure of the oxypnictide superconductor LaO(1-x)FxFeAs: evidence for magnetoelastic coupling

TL;DR

This study investigates the crystal and magnetic structures of LaO(1-x)FxFeAs superconductors using neutron and X-ray diffraction, revealing strong magneto-elastic coupling and larger magnetic moments than previously reported.

Contribution

It provides detailed structural and magnetic characterization of LaO(1-x)FxFeAs, highlighting the presence of magneto-elastic coupling and revised magnetic moment measurements.

Findings

Magnetic symmetry similar to ReOFeAs and AFe2As2.

Ordered magnetic moment of 0.63μB at 2K in undoped LaOFeAs.

Magnetic order persists up to 4.5% F doping, absent at 6% F.

Abstract

High-resolution and high-flux neutron as well as X-ray powder-diffraction experiments were performed on the oxypnictide series LaO(1-x)FxFeAs with 0<x<0.15 in order to study the crystal and magnetic structure. The magnetic symmetry of the undoped compound corresponds to those reported for ReOFeAs (with Re a rare earth) and for AFe2As2 (A=Ba, Sr) materials. We find an ordered magnetic moment of 0.63(1)muB at 2 K in LaOFeAs, which is significantly larger than the values previously reported for this compound. A sizable ordered magnetic moment is observed up to a F-doping of 4.5% whereas there is no magnetic order for a sample with a F concentration of x=0.06. In the undoped sample, several interatomic distances and FeAs4 tetrahedra angles exhibit pronounced anomalies connected with the broad structural transition and with the onset of magnetism supporting the idea of strong magneto-elastic coupling in this material.