Iron spin-reorientation transition in NdFeAsO

TL;DR

This study investigates the low-temperature magnetic structure of NdFeAsO, revealing a spin-reorientation transition of the Fe sublattice driven by Nd magnetic ordering, using neutron diffraction and symmetry analysis.

Contribution

It provides the first detailed neutron diffraction analysis of NdFeAsO's magnetic structure, identifying a spin-reorientation transition and clarifying the magnetic moments of Fe and Nd.

Findings

Fe moments point along the c-direction at low temperature

Nd moments align along the a-direction

Fe moment remains approximately 0.5 Bohr magnetons

Abstract

The low-temperature magnetic structure of NdFeAsO has been revisited using neutron powder diffraction and symmetry analysis using the Sarah representational analysis program. Four magnetic models with one magnetic variable for each of the Nd and Fe sublattices were tested. The best fit was obtained using a model with Fe moments pointing along the c-direction, and Nd moments along the a-direction. This signals a significant interplay between rare-earth and transition metal magnetism, which results in a spin-reorientation of the Fe sublattice upon ordering of the Nd moments. All models that fit the data well, including collinear models with more than one magnetic variable per sublattice, were found to have an Fe moment of 0.5 BM and a Nd moment of 0.9 BM, demonstrating that the low-temperature Fe moment is not substantially enhanced compared to the spin-density wave (SDW) state.