Structure and Magnetic Order in the NdFeAs(O,F) Superconductor System

TL;DR

This study investigates the magnetic and structural properties of NdFeAs(O,F) superconductors, revealing magnetic ordering in NdFeAsO and its absence in the fluorine-doped superconducting phase, highlighting the interplay between magnetism and superconductivity.

Contribution

First neutron diffraction analysis of NdFeAsO showing magnetic order and structural similarities to LaFeAsO, and demonstrating suppression of magnetism in superconducting NdFeAsO0.80F0.20.

Findings

NdFeAsO exhibits antiferromagnetic order below 1.96 K.

Magnetic moments are 1.55 μB for Nd and 0.9 μB for Fe at 0.3 K.

Superconducting NdFeAsO0.80F0.20 shows no magnetic order down to 1.5 K.

Abstract

The transition temperature Tc~26 K of the recently discovered superconductor LaFeAs(O,F) has been demonstrated to be extremely sensitive to the lanthanide ion, reaching 55 K for the Sm containing oxypnictides. Therefore, it is important to determine how the moment on the lanthanide affects the overall magnetism in these systems. Here we report a neutron diffraction study of the Nd oxypnictides. Long ranged antiferromagnetic order is apparent in NdFeAsO below 1.96 K. Rietveld refinement shows that both Fe and Nd magnetic ordering are required to describe the observed data with the staggered moment 1.55(4) Bohr magneton per Nd and 0.9(1) Bohr magneton per Fe at 0.3 K. The other structural properties such as the tetragonal-orthorhombic distortion are found to be very similar to those in LaFeAsO. Neither the magnetic ordering nor the structural distortion occur in the superconducting sample NdFeAsO0.80F0.20 at any temperatures down to 1.5 K.