Altermagnetism revealed by polarized neutrons in MnF(2).

Polarized inelastic neutron scattering shows MnF2 is altermagnetic, with magnon-band splitting tied to long-range dipolar coupling and a chirality that flips sign between modes.

• Why it matters: Altermagnets require direct spectroscopic confirmation of symmetry-enforced spin-split bands, and existing evidence from other compounds motivates testing MnF2 with mode-resolved probes.
• What they did: The study used polarized INS on MnF2, including a domain-biased sample, to measure magnon spectra and the neutron-scattering cross section’s chirality across two magnon modes.
• The result: The observed nonzero chirality reverses sign between the magnon modes, providing clear spectroscopic evidence of altermagnetism in MnF2 and enabling polarized INS to characterize altermagnets via fine magnon-structure sensitivity.

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