FeF2 is a prototypical rutile antiferromagnet recently proposed as an altermagnet, with a magnetic symmetry that permits spin-split electronic bands and chiral magnons. Using very-high-resolution inelastic neutron scattering on a single crystal of FeF2, we show that the dominant source of magnon splitting is in fact the long-range dipolar interaction rather than altermagnetic exchange terms. At momenta where the dipolar splitting vanishes, we observe additional broadening due to altermagnetic chiral splitting and estimate this splitting to be ∼35 μeV. Polarized measurements further reveal that, where dipolar splitting is present, the chiral magnon modes become mixed and the resulting modes are predominantly linearly polarized, with at most a small chiral component. These findings highlight the significant effect of dipolar interactions on magnon chirality, particularly when altermagnetic interactions are weak.
@article{arxiv.2601.04303,
title = {Altermagnetic and dipolar splitting of magnons in FeF$_2$},
author = {J. Sears and V. O. Garlea and D. Lederman and J. M. Tranquada and I. A. Zaliznyak},
journal= {arXiv preprint arXiv:2601.04303},
year = {2026}
}