Direct evidence for the magnetic ordering of Nd ions in NdFeAsO by high resolution inelastic neutron scattering

TL;DR

This study provides direct evidence of Nd magnetic ordering in NdFeAsO through high-resolution inelastic neutron scattering, revealing hyperfine splitting related to Nd nuclear levels and their temperature-dependent behavior.

Contribution

It is the first to directly observe Nd magnetic ordering in NdFeAsO using hyperfine-split nuclear transitions via neutron scattering.

Findings

Inelastic peaks at 1.600 μeV indicating hyperfine splitting

Peaks merge with elastic peak around 6 K

Hyperfine field caused by Nd magnetic ordering

Abstract

We investigated the low energy excitations in the parent compound NdFeAsO of the Fe-pnictide superconductor in the $\mu$eV range by a back scattering neutron spectrometer. The energy scans on a powder NdFeAsO sample revealed inelastic peaks at E = 1.600 $ \pm 0.003 \mu$eV at T = 0.055 K on both energy gain and energy loss sides. The inelastic peaks move gradually towards lower energy with increasing temperature and finally merge with the elastic peak at about 6 K. We interpret the inelastic peaks to be due to the transition between hyperfine-split nuclear level of the $^{143}$Nd and $^{145}$Nd isotopes with spin $I = 7/2$. The hyperfine field is produced by the ordering of the electronic magnetic moment of Nd at low temperature and thus the present investigation gives direct evidence of the ordering of the Nd magnetic sublattice of NdFeAsO at low temperature.