Spatial Inhomogeneity in RFeAsO1-xFx (R =Pr, Nd) Determined from Rare Earth Crystal Field Excitations

TL;DR

This study uses inelastic neutron scattering to analyze crystal field excitations in RFeAsO1-xFx compounds, revealing inhomogeneous charge environments caused by fluorine doping and clarifying the role of rare earth magnetism in superconductivity.

Contribution

It demonstrates how fluorine doping creates distinct charge environments and shows that rare earth magnetism does not enhance Tc in these materials.

Findings

Fluorine doping introduces additional crystal field excitations.

Charge environments around rare earth ions are inhomogeneous.

Rare earth magnetism does not correlate with Tc enhancement.

Abstract

We report inelastic neutron scattering measurements of crystal field transitions in PrFeAsO, PrFeAsO0.87F0.13, and NdFeAsO0.85F0.15. Doping with fluorine produces additional crystal field excitations, providing evidence that there are two distinct charge environments around the rare earth ions, with probabilities that are consistent with a random distribution of dopants on the oxygen sites. The 4f electrons of the Pr3+ and Nd3+ ions have non-magnetic and magnetic ground states, respectively, indicating that the enhancement of Tc compared to LaFeAsO1-xFx is not due to rare earth magnetism.