Chiral magnetnetism in an altermagnet (MnF2)

Abstract

Symmetry informed diffraction patterns for magnetically ordered MnF2 illuminated by x-rays tuned in energy to a Mn atomic resonance depend on circular polarization in the primary beam. The change in intensity of a Bragg spot with a change in handedness establishes a chiral signature for the fully compensated collinear antiferromagnet. The signature is calculated for electric dipole (E1) and electric quadrupole (E2) axial absorption events. Polar E1-E2 absorption events are forbidden by inversion symmetry in Wyckoff positions assigned to Mn ions in the established MnF2 magnetic symmetry. It is compatible with atomic altermagnetism, and the corresponding order parameter contributes to E2-E2 and magnetic neutron Bragg diffraction patterns. Moreover, spin-flip patterns from polarized neutron diffraction depend on electronic quadrupole and octupole moments that are zero for the nominal 3d5 configuration of Mn2+, which make them good tests of the actual electronic structure.