Inelastic neutron scattering investigation of the crystal field excitations of NdCo$_5$

TL;DR

This study uses inelastic neutron scattering to analyze crystal field excitations in NdCo$_5$, revealing detailed energy levels and the importance of exchange fields, which enhances understanding of rare-earth permanent magnets.

Contribution

First experimental determination of crystal field levels in NdCo$_5$ incorporating exchange fields, highlighting the significant role of specific crystal field parameters.

Findings

Identified crystal field levels at 28.9 and 52.9 meV in NdCo$_5$

Exchange field $B_{exc}$ is larger than previously estimated

Both crystal field parameter $A_6^6raket{r^6}$ and $B_{exc}$ are crucial for modeling

Abstract

We present an inelastic neutron scattering study of the crystal electric field levels in the intermetallic ferrimagnets RECo$_{5}$ (RE = Nd and Y). In NdCo$_{5}$, measurements at $5~$K reveal two levels at approximately 28.9 and 52.9 meV. Crystal field calculations including the exchange field $B_{\textrm{exc}}$ from the Co sites account for both of these, as well as the spectrum at temperatures above the spin-reorientation transition at $\sim 280$~K. In particular, it is found that both a large hexagonal crystal field parameter $A_{6}^6\langle r^6 \rangle$ and $B_{\textrm{exc}}$ are required to reproduce the data, with the latter having a much larger value than that deduced from previous computational and experimental studies. Our study sheds light on the delicate interplay of terms in the rare-earth Hamiltonian of RECo$_5$ systems, and is therefore expected to stimulate further experimental and computational work on the broader family of rare-earth permanent magnets.