Magnetic excitation spectrum and hierarchy of magnetic interactions in ErFeO3

TL;DR

This study uses neutron spectroscopy to analyze the magnetic excitation spectrum of ErFeO3, revealing the hierarchy of magnetic interactions and detailed spin dynamics in this orthoferrite.

Contribution

It provides a comprehensive experimental and theoretical analysis of ErFeO3's magnetic excitations, including exchange parameters and the interplay between Er and Fe sublattices.

Findings

Fe$^{3+}$ spin waves span 9-65 meV with well-captured dispersions

CEF levels of Er$^{3+}$ are split and dispersive, influenced by exchange interactions

Hierarchy of interaction scales characteristic for orthoferrites is revealed

Abstract

We report a comprehensive investigation of the excitation spectrum of ErFeO$_3$ orthoferrite by means of time-of-flight neutron spectroscopy. The spectrum consists of two distinct components: strongly dispersive spin wave excitations of the Fe$^{3+}$ sublattice spanning $\approx$~9 - 65 meV, and crystal electric field (CEF) excitations of Er$^{3+}$ ions below 36 meV. The observed spin wave dispersions and spectral weight are well captured within linear spin wave theory, enabling extraction of the key Fe-Fe exchange parameters. Low-energy incident neutrons with their enhanced energy resolution, further revealed the dispersive character and splitting of Kramers-degenerate CEF levels. We show that the dispersion is caused by the exchange coupling between Er$^{3+}$ ions, while the degeneracy is lifted by interactions between the Er$^{3+}$ and Fe$^{3+}$ sublattices. We further explore the influence of dipolar and antisymmetric exchange interactions with the focus on the magnetic ground state of ErFeO$_3$, with particular attention to the low-temperature spin arrangement. Taken together, our results provide a detailed account of the spin dynamics in ErFeO$_3$ and reveal a hierarchy of interactions scales characteristic for orthoferrites.