F. de Almeida Passos | Searcharxiv

arXiv2025

Revisiting the magnetic ground states of RECo$_5$ permanent magnets

In light of recent improvements in the theory of rare earth magnets, as well as the availability of improved neutron powder diffraction data on these materials, we revisit the magnetic single-ion properties of SmCo$_5$ and the magnetic structures of YCo$_5$ and NdCo$_5$. From neutron diffraction patterns in a wide range of temperatures between 3 K and 800 K, we obtain the thermal coefficient expansion and the magnetic moment values for the latter two materials. For SmCo$_5$, we fit existing neutron spectroscopy data with a model recently used for NdCo$_5$ to obtain the crystal field parameters, which are essential to determine the low-lying energy scales that set the Hamiltonian. Our results may trigger new experimental and theoretical studies towards a new route for the realization of permanent magnets.

cond-mat.str-el↗

arXiv2023

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

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.

cond-mat.str-el↗